Most of us are exposed to it at one time or another in our daily routines. Some hardly even notice it, accepting it as part of their everyday environment. But to those living in close proximity to busy highways, it can be a major source of annoyance. It can interrupt sleep, interfere with conversation, and cause stress. In recent years, more and more people have moved out of cities and into the suburbs or more rural communities. The result is larger numbers of people commuting greater distances, thus requiring larger and more efficient highways. Relatively little use roadways become busy thoroughfares that require expansion to meet the demand. And many of these people want easy access, resulting in residential development in close proximity to the busy highways. The noise levels from these highways are often above the recommended levels established by the Federal Highway Administration, as well as state and local municipalities. Noise barriers have been shown to be an effective method of reducing the noise levels in communities adjacent to highways. This video will explain the basics of traffic noise and barrier performance, describe various types of barriers, and discuss concerns related to barrier maintenance and safety. Traffic noise originates primarily from three sources. Truck exhaust stacks, tires interacting with the pavement, and vehicle engines. These sources each produce energy that in turn translates into tiny fluctuations in atmospheric pressure as the sources move and vibrate. These pressure fluctuations are measured in units of micro Pascal and range from 20 to 200 million. Because of this wide range, these fluctuations, called the sounds energy, are measured on a logarithmic scale known as the decibel scale. A value of zero decibels is equal to a pressure fluctuation of 20 micro Pascal and corresponds to the threshold of hearing for most humans. A value of 140 decibels is equal to a pressure fluctuation of 20 million micro Pascal, which is the threshold of pain for most humans. Following are sounds encountered in daily life and their approximate decibel values, so that you can begin to equate numbers with actual sources. A quiet suburban neighborhood will exhibit an average sound level of about 40 decibels. Normal conversation occurs at around 65 decibels. That sounds great. It was fun. It was the first time I've been for a number of years. You've been to England often? Years ago. A gas lawnmower of 31 meters away will create a sound level of approximately 70 decibels. A diesel truck at highway speeds 15 meters away will achieve a maximum level of about 85 decibels. A state-of-the-art jet aircraft at 305 meters altitude will create a maximum level of about 90 decibels. With these common examples in mind, traffic on a busy highway 15 meters away can average as much as 80 decibels during peak travel periods. Sounds typically occur over time, or in other words, they have a particular duration. A graphic time history of neighborhood sound levels over a one-hour period might look like this. The peaks and valleys in the level recording indicate different types of activity. This is the maximum level that occurred during the period. A common noise metric used to describe traffic noise is the hourly equivalent sound level. It can be thought of as the average level for a one-hour time period, although the mathematics are a bit more cumbersome. Hourly LEQ is the most commonly used noise metric for designing highway noise barriers. Typically, the hourly LEQ used for barrier design is for the hour in which traffic is heaviest, but still flowing freely. Not only does sound have loudness and duration, but it also has a frequency or tonality measured in hertz, or cycles per second. Most humans can hear in a range from 20 hertz to 20,000 hertz. As a point of reference, middle C on a piano has a frequency of 261.6 hertz. The notes on a typical 88-key piano range from 28 hertz to 4,186 hertz. Blanche, this is no time for a pause. The spoken voice typically has a range of 70 to 200 hertz for a man and 140 to 400 hertz for a woman. You find anyone else you think you can work with? Blanche, it's not like Kyrie and Maid. A collaboration is a very sensitive relationship. Following our tones at 250 hertz, 500 hertz, 1,000 hertz, and 2,000 hertz. Notice how the tones, although played at the same level, did not sound equally loud. The last tone at 2,000 hertz should have sounded the loudest.  To account for this, community noise is usually measured using what is known as an A-weighted response network. A-weighting emphasizes sounds between 1,000 hertz and 6,300 hertz. And D emphasizes sounds above and below that range to simulate the response of the human ear. Sound levels measured using the A-weighting network are often denoted by the symbol DBA. Since normal conversation occurs at about 65 decibels, any noise which has a level substantially above this may cause annoyance. Noise barriers reduce the sound which enters a community from a busy highway by either absorbing it, reflecting it back across the highway, or forcing it to take a longer path. This longer path is referred to as the diffracted path. Diffraction, or the bending of sound waves around an obstacle, can occur both at the top of the barrier and around the ends. If designed properly, a noise barrier should be tall enough and long enough so that only a small portion of noise diffracts around the edges. In most instances, any noise which is transmitted through the barrier can be effectively neglected since it will be at such a low level relative to the diffracted noise. Properly designed noise barriers can attain a reduction in noise level of as much as 10 decibels, which is equivalent to a perceived halving in loudness for the homes directly behind the barrier, referred to as the first row of homes. The reduction in noise level due to a barrier is termed insertion loss. A halving in loudness requires a tenfold decrease in sound energy. Such a reduction is readily perceived as substantial by the adjoining community. To demonstrate this reduction, here is a busy highway with a sound level of 80 DBA. Here is the same sound source reduced to 70 DBA. To give the viewer a general sense of barrier performance, a 5 DBA reduction can be expected for receivers whose line of sight to the roadway is blocked by the barrier. A general rule of thumb is that each additional 1 meter of barrier height above line of sight blockage will provide about 1.5 DBA of additional reduction. For those residents not directly behind the barrier, an insertion loss of 3 to 5 DBA can typically be provided. An insertion loss of 3 DBA is generally just slightly perceptible to the human ear. Here is the same busy highway, first at 80 DBA and then at 77 DBA. As you notice, it is very difficult to discern a difference. Can the installation of a barrier increase sound levels for those living on the opposite side of the highway? Reflections from a barrier on the opposite side of the roadway can theoretically result in a 3 DBA maximum increase. Practically, some of the sound is diffracted over the barrier and much of the reflected sound energy is dispersed by passing vehicles. Research has shown that typically a 1 or 2 DBA increase can be expected. Such an increase is not readily perceptible to the human ear. What happens when barriers are present on both sides of the highway? Sound reflected between reflective barriers may cause degradations in each barrier's performance anywhere from 2 to as much as 6 DBA. In other words, a single barrier with an insertion loss of 10 DBA may only realize an effective reduction of 4 to 8 DBA if another barrier is placed parallel to it on the opposite side of the highway. Fortunately, the problems caused by both single and parallel barriers can be minimized using one or a combination of these three methods. For parallel barriers, ensure that the distance between the two barriers is at least 10 times their average height. A 10 to 1 width to height ratio will result in an imperceptible degradation in performance. Applying acoustically absorptive material on either one or both barrier facades is another solution. The amount of noise that a barrier absorbs is typically expressed in terms of a noise reduction coefficient, or NRC. The NRC can range from 0 to 1. 0 means the barrier will reflect all the sound that strikes it, and 1 means the barrier will absorb all the sound. A typical NRC for an absorptive barrier ranges from 0.6 to 0.9. And finally, tilt one of the barriers outward away from the road. This solution, however, must consider structures higher than the opposite barrier, because they may be adversely affected by the reflected sound. Barriers can be categorized into two general types, earth berms and walls. Earth berms have the ability to blend more naturally with the surroundings that require large amounts of space to achieve significant noise reduction. Often because of limited right of way, earth berms must be transitioned into walls to accommodate highway overpasses. For reasons such as this, and due to the space requirement of berms, wall barriers are far more common. Wall barriers should be designed and constructed with visual aesthetics in mind. Variations in color, texture and form are common ways to achieve this objective. There are two schools of thought on how to make a wall barrier visually acceptable. It can be designed to stand out from its surroundings and become a visual focus. This approach can be costly to build and maintain. And if the barrier is too visually interesting, it may divert the motorist's attention away from the roadway. Or a barrier can be designed to blend into its surroundings and have little visual impact. These two schools of thought are best exemplified when looking at design considerations associated with barrier ends. If a barrier has an abrupt end, it will stand out and look more unnatural. There are methods to lessen this unpleasant characteristic. A barrier's height can be stepped down gradually. A barrier's last one or two panels can be sloped. Or a barrier's end panels can be angled inward toward the residence. This technique helps reduce diffraction of noise around the ends. Sometimes barrier ends can be transitioned into an earth berm. And finally, large plants or bushes can be used. In addition to visual quality, the type of material chosen for a wall barrier in a given location is an integral part of the design process. And is dependent on a variety of other factors, including cost, weight, durability, and maintenance. The needs of the nearby community as well as those of the motorists must also be considered. If a barrier is to blend into its surroundings, it should be constructed of material indigenous to the area. Concrete, metal, and masonry block may be used in urban areas, while wood may be more appropriate in suburban or rural areas. Masonry block is a commonly used material for barriers. It is relatively inexpensive to use and maintain, massive enough to allow little sound transmission, and strong enough to survive high winds and minor vehicle impacts. However, this type of wall may become monotonous if visual relief is not provided. Using blocks of various colors and shades can make a wall more aesthetically pleasing. Here, blocks of different colors were used to represent the city's skyline. Precast concrete panels are another popular barrier material. And like masonry blocks, concrete panels are relatively inexpensive to install and maintain, allow for negligible sound transmission, and are able to survive winds and minor vehicle impacts. Because the panels are precast, they can be installed in relatively short periods of time, reducing inconvenience for residents and motorists. Pictures and designs can be precast into the concrete for visual appeal. This panel barrier has a stone wall finish on the motorist side, and has an exposed aggregate finish on the resident side. These concrete panels have been arranged in a zigzag configuration. This design is advantageous because it is structurally sound without the use of a foundation, and is visually pleasing to motorists because it provides a variation in form. Wood barriers have the advantage of looking more natural, and are thus considered to be more aesthetically pleasing. Because wood barriers are relatively lightweight, they can be used on bridges or other structures where weight is a consideration. However, if treated improperly, wood barriers can be costly to maintain. Moisture and temperature variations can necessitate frequent painting. Warping and cracking are also a maintenance consideration for wood barriers. Metal can also be used as barrier material. It is typically precast, can be installed relatively quickly, and is lightweight for use on bridges and other structures. Unfortunately, however, metal barriers can be difficult to maintain if subjected to vehicle impacts. And once a metal barrier's anti-corrosive finish has been compromised, it may rust and deteriorate further, defeating the aesthetic objective of a barrier. As previously mentioned, earth berms can be more naturally appealing, and once landscaped are the easiest to maintain. They are not vulnerable to costly damage by vehicle impact or high winds, and can be very economical if fill material and right-of-way space is available. If insufficient right-of-way space is available, a wall can be built on top of a small berm. This is usually more cost-effective than building a wall without a berm. Additionally, the slope of the berm provides an area for extensive landscaping. There are several innovative barrier designs in use throughout the country. Some are still in the experimental stage, while others are being used with varying degrees of success. Transparent barriers are being used for maintaining scenic views and for ensuring that business advertisement isn't hampered. It is often necessary, however, for municipalities to underwrite the costly maintenance and cleaning of these barriers to help keep them transparent. Here, a barrier was constructed using a combination of masonry block and transparent panels. However, special care should be taken when using transparent panels so that glare from vehicle headlights does not cause a potential safety problem. Recently, there has been proposals for the use of recycled materials, such as tires, either reprocessed as seen here or in discarded form. Plastic is also a potential recycled material for use as noise barriers. Another innovative design uses stacked concrete troughs, which are filled with soil and then planted with vegetation. After the vegetation has grown out, the presence of the barrier grows almost unnoticed. These stone-filled wire blocks are extremely cost-effective because the stone was taken from the field created when the highway was under construction and are inexpensive to maintain. Oftentimes, residents resistant to barrier construction suggest that planting a row of trees may solve their noise disturbances. Unfortunately, a limited number of trees and shrubs will only have an out-of-sight, out-of-mind effect. In addition, any benefit deciduous trees may have in summer will be lost in winter. For all types of barriers, it is important that maintenance and safety factors be considered. Graffiti is one such maintenance factor. This is a masonry block barrier that originally used different colored blocks for aesthetic appeal. However, graffiti made it necessary to paint the wall, thus losing the effect. The transparent barrier shown earlier was marred by graffiti scratched into its surface. There are several types of anti-graffiti treatments which help to ease maintenance concerns. And municipalities are adopting innovative approaches for both preventing graffiti and encouraging an active community role in the preservation of barriers. It should also be kept in mind that the choice of a barrier surface can naturally aid in the prevention of graffiti. This exposed aggregate finish makes graffiti defacement difficult. This same idea applies to the stone-filled wire blocks shown earlier. Perhaps the most graffiti-resistant barrier of all is the earth berm. However, landscaping is a far more concern for earth berms as compared to wall barriers. From a maintenance standpoint, properly planned and maintained landscaping discourages littering as well as graffiti. Plants that are native to the area and require little irrigation will also be more successful than those requiring extensive pruning, mowing, and watering. In northern climates, consideration should be given to plants which are resistant to the effects of sand and road salt. And all barriers must be placed far enough from the roadway to allow for cloud snow. Otherwise, snow removal costs will be a factor. Often, the area between the right-of-way fence and a barrier is ignored and becomes overgrown, causing residents to look unfavorably on an otherwise effective noise barrier. Residents usually find an agreement allowing them to use this land in return for its upkeep, quite acceptable. Some states have turned this area into playgrounds or pedestrian and bike paths. Safety is also an important consideration in barrier design. A barrier creating poor drainage can compromise safety for both residents and motorists. This system includes stormwater grates on both sides that carry water under the barrier and roadway. And this barrier has a gravel sub-base which allows some water to pass under it. For barriers of considerable length, some form of emergency access should be incorporated into the design. Here, doors were built into the barrier. A gap with overlapping barrier ends can be built with a negligible reduction in performance. A generally accepted rule of thumb is that the ratio between overlap distance and gap width should be at least 4 to 1 to reduce degradation of barrier performance. Easy accessibility to fire hydrants can mean the difference between life and death. This panel on a concrete barrier has a knockout receptacle to gain access to a fire hydrant in the adjacent community. Similarly, this barrier has a built-in door which is marked by a blue fire hydrant placard to indicate the location of the hydrant. And this barrier has fire hose receptacles built into it. For nighttime safety, lighting standards must be incorporated into the design that do not compromise the barrier's performance. To be most effective, a barrier should either be as close to the residential area it protects, or as close to the road as possible. The latter case can pose another safety issue. For a barrier less than 10 meters from the roadway, some form of vehicle impact protection will be necessary. Here, a guardrail has been placed in front of the barrier. And here, a jersey barrier has been incorporated into the design. A barrier must not block the line of sight between an on-ramp and the highway being traveled. Nor should a barrier block a motorist's view of the intersecting roadway at a stop sign or traffic light. We have seen that the quality of life is enhanced for those living next to busy highways through the use of noise barriers. A 10 DBA reduction, or a halving in the loudness of noise, can be realized by those immediately adjacent to the barrier, and a 3 to 5 DBA reduction by those farther away. Many non-acoustic benefits can be realized from the construction of a noise barrier. The two general types of noise barriers, earth berms and walls, each offer their own unique advantages. Maintenance and safety factors are equally important in ensuring the success of a barrier's design. Planned and maintained noise barrier can become a significant part of the environment and a valuable community asset.


Hey guys, welcome back to Tip Tuesday. I'm Kristen, sister number two from Six Sisters Stuff, and today we're talking about the Instant Pot and things you don't want to do when using one.  I'll be honest, mine sat in my box for about three months before I dare to finally open it.  Here are my 10 don'ts when using the Instant Pot. Number one, don't just jump in, turn it on, and expect everything to work without reading the instructions. The instructions are the most important thing when using your Instant Pot. I know this sounds ridiculous, but there are so many who don't use it. So please, please use the instructions. Now, in case you didn't know, the Instant Pot is not a slow cooker. You can't turn it on and expect it to pressurize and cook like a slow cooker can. You need at least a half a cup to a cup of water in the pressure cooker or it won't work. Now there is a little knob at the top of your pressure cooker which is preventing or sealing. So you have to make sure it's always on sealing or again, your pressure cooker will not pressurize and it will not cook. Venting is for when it's all done cooking. It's called a quick release and you turn it to venting. But for now, when you want to pressurize it, be sure it's on sealing. I've done this many times, stuck something in here and it didn't cook, I couldn't figure out why. Oh, because I was on venting, I'm not sealing. Do not stick your hand over the vent when you're doing, when a recipe calls for a quick release. If you do, you will burn your hand and yes, I did experience this. So I would suggest using a hot pad or being very careful making sure your hand is not in the way when you are ready to vent. Do not overfill the instant pot because one, it takes forever to pressurize. Two, sometimes it doesn't even pressurize and three, sometimes it won't even close if you're overfilled. So your food doesn't cook as evenly, it could burn, it could not cook at all. Lots of reasons why you should not overfill it. And thankfully, they have a max line and I would suggest doing one line underneath the max line. Do not place the still bowl on the stove top. Now I didn't do it myself, thankfully, but I have seen pictures of other people who have put it on the stove top and turned it on, this is not for the stove top, it is only for the instant pot. So make sure it just stays there. As you open your instructions and read them like you're supposed to, right? Yeah, you will understand these words like quick release and venting. Be sure when you're making foamy food. So things that cause foam like rice, beans, any type of grain, when I do like a ton of potatoes, when you do really thick soup, anything that causes foaming when it pressurizes. If you do a quick release, even though some says do quick release, if you do a quick release, you will have soup or whatever foam that is coming from that will be all over your kitchen. So just beware when it's a foamy recipe, be sure you can do quick release. I'll show you real quick. So you're on ceiling to do quick release, you can turn it quickly and quick release that way, then you won't have explosions because no one wants explosions in their kitchen. I've done it multiple times, it's awful to clean up. This is kind of an obvious one, but I've done it before, so that's why it's on the list. You can plug this baby in, you can have it all set up, but if you do not set the timer, it is not gonna pressurize and you're gonna be ready for dinner in about a half an hour and realize you forgot to set the timer and your food is not cooked. So be sure to always set the timer on your Instant Pot. Most people when they get their Instant Pot and they get an awesome recipe, they're so excited because oh, it only takes 20 minutes. Well, just be sure to add an extra 10 to 20 minutes on to that final time because it really does take 10 to 20 minutes for it to pressurize. People get frustrated and are angry at the people who write the recipes and so just be sure it is gonna take an extra 10 to 20 minutes to pressurize. Now obviously there are a lot more tips and tricks that go along with the Instant Pot, these are just the ones that I had experience with that I thought would be helpful for new people who have an Instant Pot. Now, I do have a suggestion. If you are brand new to the Instant Pot community, I highly suggest going to the Facebook group. It's called Instant Pot Recipes. They literally have hundreds of recipes you can try that people actually have tried and taken pictures and share with you. It's a great group to be a part of. So if you're new to that, go check out that Facebook group. Well, I hope these Instant Pot don'ts can help you as you're making recipes for your family. Be sure to give us a big thumbs up or a comment if you like our Instant Pot post or if you wanna see more Instant Pot recipes. And don't forget, if you haven't done it, subscribe to our channel. All right guys, we'll see you later.


There's just so much you can learn and you can talk to people who actually work on a lot of the technologies that you're using at work. And then there's always the opportunity to meet really amazing people from all around the world, so I love that as well. Linux Foundation events are a great opportunity to engage with the community, see what they're looking for in our solutions, as well as meet with developers that might join our open source community and help extend our own project. And so we wanted to be part of the conversation and get that feedback.


Hey traders, this is Tosh. I go by T Bradley 90 in MIC my investing club chat today One of our moderators named Chicago trader real name Matt does a video for us today where he dives into the BP TH Fundamental analysis and this is episode 11 and we've got a preview for you guys today If you want to watch the full video then become an exclusive member. All right, let's get into it Hey, what's going on guys Chicago trader check them with the weekly fundamental video Hope you guys are having a nice week of trading and all the chaos with the BP T8. I Will go through this real quick so they did the offering Monday or Tuesday Monday morning Now I wanted to show you guys something in the press release that I had kind of missed initially She had tells you the float here something that I missed Was Just go back up. Yeah, so the delivery of the shares are on March 14th, which would be The end of closed today, I believe it's either today or tomorrow But this won't be added to the float until March 14th and definitely on March 15th Obviously, so the float would be you know right around 2.4 million and then it reduces You know what they have to close that to be above the 75 million dollar shelf So my apologies for kind of messing that one up. I'd actually You guys would be surprised if you guys have questions. You can email You know investor relations of the CFOs and this guy actually got back to me twice Which is a record you're lucky to get one and I kind of clarified it that you know, they could be You know, it's gonna be delivered this day and then that's when they're added to the flow. So Guess how many questions any names? I know a lot of you guys DM me throughout the day Which I love to answer the questions and try to be as helpful as possible, but yeah, this was just a QB and It'll be interesting. I I don't like to make predictions on when something's going to offer but You know, they've supported BP th fairly well here after the offering My guess and against a guess would be either Friday after the closer Monday morning They can support it that high because You know some of these Brokers that charge the huge overnight fees 3x, you know every day and then you know those There's those go into the weekend as well or 7x or whatever those, you know, you guys are paying Friday's kid, you know, it's not a comment if it's being held up for it to be you know Kind of squeeze out and people just cover at the end of the day on a Friday and Push it up a little bit higher not wanting to pay, you know those ridiculous fees But again, just my theory be interesting to see how it plays out. So I haven't really tried to stop very much Hey traders, this is Tosh. I go by T Bradley 90 in the my investing club chat Just wanted to reach out and say if you have any questions about M. I see joining M. I see maybe you're a member already You have three ways to contact myself personally and through M. I see you can hit our social media You can hit me through pms and chat or you can contact us through my email at Tosh at my Investing club calm. That's Tosh at my investing club calm I will get back to you in a timely manner And I'm saying this because I'm here to help and I don't want anybody to be afraid to reach out and ask any question That they have we are here for you guys. All right. See you guys


This lecture is regarding the reactions of olefins or the reactions where olefins are the prime actors in the whole scene. There are two major reactions that we will be talking about. One is the oligomerization, the other is the polymerization of olefins. Both of them are probably multi billion dollar industries. There is a large demand for products that are generated from simple olefins like ethylene and propylene. So, it is important that we look at the chemistry behind these systems. Oligomerizations are basically talking about systems where the molecule for example, you have an alkene. If you take something like 4 alkenes and if you end up with this product, you have a system where you have oligomerized or you have combined together several of these olefins. Then it becomes a more useful product than ethylene itself, which is useful, but not necessarily in the way a tetramer of the ethylene is useful. So, it is important to look at these molecules or the molecules, the metal complexes which will carry out such oligomerizations. A large number of molecules appear to do this and the challenge is to do it specifically, meaning you want only the octene, you want only the one octene. So, you do not want this and you also want, you do not want the molecule to proceed to hexene when you are trying to synthesize octene. So, this type of specificity in the position of the double bond and in the oligomerization number that makes the whole chemistry challenging. We have already looked at one type of chemistry where multiple alkenes were stitched together to generate different molecules. The oligomerization that we discussed in detail, just to remind you of what is possible was the cobalt catalyzed cyclotrimerization of acetylene to give you arenes. Arenes for the product, simple alkenes were starting materials. So, you stitched together three alkenes in order to generate an arene. This was done by an oxidative addition mechanism, where the cobalt which is a cobalt one species oxidatively added and at the same time coupled to carbon fragments. A similar reaction could be envisaged with alkenes. So, you can take alkenes, put two alkenes and then you would get a metallocyclopentane and that could be used to stitch together a variety of alkenes. So, the two processes that can happen are one direct transfer of hydrogen from the beta position to the alpha dash carbon. The other is a transfer of hydrogen from the beta position, which is this position to the metal and then a second reductive elimination to the alpha dash carbon. So, in either mechanism it is the beta hydrogen, which is transferred to the alpha dash carbon. Now, it turns out that butene is a useful molecule, but it would be valuable to have hexene as a product. So, that means you need to trimerize an olefin and the synthesis of alpha olefins. That means where the double bond is present in the alpha carbon is very important for the production of a variety of materials used in bulk quantities in the industry. These are listed here. That is low density polyethylene, plasticizers, detergents and so on. So, it was only recently in 1997 that a very clean catalyst was discovered by this person Jolly, who figured out that chromium is a suitable metal for carrying out this oxidative coupling of three ethylenes to produce hexene. The mechanism is very similar to what we had seen earlier. You combine two alkenes. In this case, two ethylenes as the most popular and most cheaply available alkene that people use to synthesize a metallocyclopentane into to insert another ethylene molecule to generate a metallocycloheptane. Now, the generation of a metallocycloheptane can result in the formation of an alkene, which will be in the alpha position due to beta hydride, beta hydrogen elimination. This beta hydrogen transfer is identical to what we had discussed earlier. It can happen directly or it can happen through a metal hydride intermediate and result in this olefin complex. Now, we know that substituted olefins are less stable than unsubstituted olefins. So, referentially you would have exchange of this hexene with these ethylene molecules in order to generate this catalytically active species which is written here. In this particular case, M equals chromium is the best option and a variety of chromium complexes have been tested for this particular reaction. You will notice that in the case of nickel, where you had a D 8 system, you are able to couple 2 ethylenes. In the case of a D 6 system, you are able to couple 3 alkenes. So, there seems to be a very strong electronic effect in the coupling of alkenes to generate the final product. You just keep this in mind as we go ahead with the discussion. So, the obvious extension for this would be to proceed to a D 4 system. In fact, if you use a D 4 system, what you expect is a tetramerization, but it turns out as late as 2002, it was discovered that the tetramerization of titanium is tetramerization of ethylene is not what you observe, but you end up with a trimerization, a very efficient trimerization of ethylene in order to generate hexene. In all these cases, we are talking about the formation of one hexene which is the more useful product. Now, there are couple of more things that we need to emphasize. This is not the only complex that has been tried. I have picked up the examples which are most efficient and probably recent in the literature. In this case, the design involves several important factors. One of them is the presence of this benzene ring in a position suitable for having this weak interaction, which is marked here with a dotted line. This stabilizes the catalytically active intermediate. Although it is a weak bond, it is a titanium 3 plus complex that is involved. You have a weak bond, but that interaction is responsible for the formation of a catalytically active species. The other important point to note is that the bridge size here, the number of carbons and the substituents present on this bridge play an important role. The best catalyst was in fact with two methyl groups at this position and also with a single carbon, so that this interaction is not too strong and it is not too weak either. I have to explain also what this particular molecule MAO is. MAO is a mysterious aluminum oxide. It is methyl aluminum oxide and it is a polymeric compound, which has been used extensively in the polymer industry. It has got a methyl aluminum bond. This methyl aluminum bond is capable of carrying out a reduction of this titanium 3 species to a lower valence species. So, this lower valence species is presumably responsible for this oxidative coupling reaction, which leads to very high selectivity, very efficient selectivity for the trimerization of ethylene. Now, let us talk a little bit more about MAO because this is a molecule, which we are going to talk about more extensively. It is basically a polymeric species, where you have a methyl aluminum bond. What does it do? It essentially removes an X minus group to the saturated aluminum, which is co-ordinatively unsaturated and which can accept an X minus to form an anionic species. Here is a possible anionic species that would be formed if the aluminum picks up an X minus from the catalytically active species. But, if it is just picking up an anionic species, one would need only one aluminum per X group that you need to remove. So, in the previous example, we had three chloride groups, which are present on the titanium. So, depending on the number of titanium chloride bonds that you want to reduce, you would need one methyl alumoxane. But, you remember that the number of methyl alumoxane molecules that are usually added to the catalytically active species is very large. This is a problem that chemists have been trying to solve and are struggling with in the polygomerization and polymerization reaction. But, let us continue with this species. What else does it do? Because you can abstract an X group and form an anion, it forms a very active species, which is stabilized because the large anion, the polymeric anion that is formed is non-coordinating. It basically prevents other anions from reaching the titanium 3 plus site. Finally, because of the methyl aluminum bond, it is highly reducing. So, that is a point that has to be added. It is highly reducing. So, it would convert the titanium 3 plus to a titanium plus or titanium zero species even. The presence of methyl alumoxane can reduce the titanium completely. So, let us just take a minute and look at the possible catalytic cycle that would be involved in the selective trimerization of polyphins. So, the mechanism that we have written here is using the titanium 1 plus species, which we have indicated here as plus 1. The oxidation state is plus 1 here. We have reduced titanium from plus 3 to plus 1. After oxidative addition, it becomes plus 3. That is the plus 3 state that is involved in this reaction. Then, back at the end of this reaction, it would come back to plus 1. After oxidative addition becomes plus 3. So, if you add 3 alkenes, so with every step you would add an ethylene molecule. You would end up with a metallocycloheptane. This metallocycloheptane has got 6 carbons, 3 ethylenes joined together. This is indicated by the 3 ethylenes, which are coming together to form a metallocycloheptane. This can now by abstraction of the beta hydrogen. The beta hydrogen elimination has been already explained previously. An identical reaction happens. Now, I have transferred it to the metal titanium here. This species can undergo a reductive elimination of these 3 of these 2 units. That gives you the olefin complex, which is the titanium 1 complex. The titanium 1 complex because it has got a hexene coordinated. It prefers the ethylene, exchanges for the ethylene and the catalytic cycle continues. So, the reaction apparently goes through this type of a catalytic cycle, which is very similar to what we have noticed for the chromium and the nickel. Now, let us just take a brief minute to ask this question. Can we avoid the MAO or the MAO? The MAO is used in very large amounts. Usually it is used in a ratio of 1 is to 1000. If the catalytically active metal is chromium, the ratio of aluminum to chromium would be at least 1000. So, this type of a excess use of MAO has been found to be essential. So, that leads to very little molecular understanding. Usually if you need a molecular understanding, one should have some stoichiometric reaction of the 2 entities that are involved. Here chromium and aluminum are present in such a large ratio that a molecular understanding is avoided. Now, the 2 important functions that we have just reviewed are that it is a good reducing agent and we have seen that it protects the active site. So, recently it has been possible as very recently it has been shown that MAO can be avoided and it has been substituted by 2 different strategies. One is to use aluminum trimethyl aluminum as a reducing agent. The other was to use a very large bulky anion. We will show this in the next slide, but basically the use of a large very large amount of aluminum has been avoided and stoichiometric amounts or close to stoichiometric amounts of trimethyl aluminum are used in this whole reaction. In this specific case, about 10 equivalents of trimethyl aluminum were added and this is a far cry from the 1000 equivalents which is usually used in order to achieve very large efficiencies of the order that is shown here. So, let us see what happens in this reaction. Here is a chromium complex that was used. It is a chromium dichloride, a dichlorocomplex of chromium with a net charge of plus 1. The net charge of plus 1 indicates that chromium is now in the plus 3 oxidation state. The bulky anion that was used was this perfluorinated butoxide ion. So, perfluorobutoxide anion tetrakis perfluorobutinoid is what you have here. Four of these coordinated to the aluminum, so much so that the single negative charge is there on the aluminum resulting in a very large bulky anion. At the same time, you have a chromium 2 plus species as a starting material. If it is treated with this activator, which is aluminum trimethyl aluminum, this is a lower case here, trimethyl aluminum, then 10 equivalents was sufficient to bring about a substantial productivity. This is the grams of polyethylene, grams of the oligomerized ethylene per gram of the chromium that is used. So, this is how the efficiency is measured. So, this is grams of ethylene oligomerized for each gram of chromium that is utilized in the reaction mixture. So, the ligand that we have here, we have not expanded it, but this is a special ligand, which has got the methoxy group on the aryl moiety, which is attached to the phosphorous. This AR has got OME group and that turns out to be critical, because it stabilizes the chromium after it is activated by the trimethyl aluminum. For the sake of comparison, the researchers have also carried out the same reaction with Mao and they have noticed that you need close to 300 equivalents of Mao in order to do carry out the same reaction in the absence of this bulky anion and in the presence of the methyl alumoxane as a reducing agent. But you will notice that the activity that you get with this bulky anion is not as good as what you would get with trimethyl aluminum oxane, but the selectivity for hexane, which is one of the important parameters is still retained. You will also realize that we have moved from a chromium 3 plus complex to a chromium probably a chromium 0 species, which is carrying out the actual reaction. One very important criterion in this whole process is that the recovered catalyst. The recovered catalyst can be used again and it has almost as good an activity when you use this ligand as the starting material itself. So, let us take a look at the recovered catalyst that they have characterized, which is I think a very significant, this is a very significant observation that they have made during the course of this reaction. They have shown that the chlorides have been removed and a co-ordinatively unsaturated species of chromium 2 plus is generated in the reaction medium. They have isolated crystalline material, which they have characterized. I have shown the crystal structure here and you will notice that the anion that you have that is the tetra alkoxy species, aluminate species, which is behaving as anion is shown here. The green fluorescent atoms are all fluorines and you can see that the whole aluminum is completely encapsulated by this fluorous sphere. So, it becomes a very large stabilizing anion and the chromium species is also covered by this very bulky phosphinoamine that we have used as a ligand. This oxygen that is there in the ortho position of the aryl group is responsible for stabilizing the chromium in its co-ordinatively unsaturated state. If you look at the crystal structure, which is freely available on the website of the journal, you would be able to understand the interactions a little more, but I have shown you one interaction on the screen right here. Using this catalyst, it was possible to catalyze the reaction very efficiently and generate one hexane in a very selective fashion. You will notice that the tendency to trimerize is fairly significant and what that tells us is, when the molecule oxidatively adds and inserts ethylene, it tends to form a cycloheptane, metallocycloheptane molecule and that has got a beta hydrogen extremely close to the metal and bringing the C1 close to the metal becomes more favorable when you have this ring size. The metal size also is important. Most of these oligomerization reactions have been carried out with 3D metal ions. 3D metal ions have been used for making the oligomers and it is not the 4D and we can see that the chances of biting the CH bond changes when you have a 3D versus 4D. So, the 3D metal turns out to be good for making oligomers. Now, in all the cases that we have mentioned including the one on titanium, where we expected a tetramerization, we saw only trimerization of the ethylene. So, it is indeed gratifying to note that eventually chemists have solved this puzzle and they have discovered a catalyst which can do tetramerization. That means, if you tetramerize ethylene, you would get octene and if you can make specifically one octene, it would be an extremely good achievement. This is exactly what the researchers have discovered and they have published this work in the Journal of American Chemical Society in 2004. So, let us just take a look again. It is a phosphinoamine that has been used and in this particular instance, they have used a very common ligand which is this diphenyl phosphino compound, where you have an isopropyl group on the nitrogen. So, you just take isopropyl amine and treat it with PPH2Cl and you would get this very easy to synthesize ligand. That ligand is abbreviated in this pink form here and the complex that they isolated and characterized is shown here and that is the complex that they used as a starting material. But in this case also, MAO was used as an activating agent. MAO was the best activating agent that has been used and they have used about 300 equivalents of MAO in a toluene solvent in order to achieve this very high selectivity for tetramerization. What is interesting is that both C6 and C8 are formed in this reaction. So, obviously that is a tendency for the chromium to add another ethylene and form a cyclononane and it is the cyclononane which has the right orientation in order to do the CH abstraction. You will notice that in the case of this ligand which they have this PNP ligand, it is possible to achieve very high selectivity for C8. What is written here is the C6 selectivity, C6 versus C8 selectivity can be seen here. So, that is 17 percent versus 68 percent C6 versus C8 in the case of DPPA and within that you will see that one hexene turns out to be about 70 percent. So, that means the remaining 30 percent of the hexene are internal olefins. Similarly, out of 70 percent or 68 percent of the C8 octene that is formed 98 percent is one octene. So, that is excellent selectivity for the one octene which is what we really need in the industry. If you look at the remaining amount it is mostly polyethylene. So, this is the polymeric species that is formed which is also formed in small amounts. So, we do not have to go through the catalyst cycle again, but suffice it to say that in the presence of large amounts of methyl alumoxane the chromium which is present here in the 3 plus state. If you draw a line here you will realize that the dimer has got 3 clorins for each chromium. So, it is a chromium in the plus 3 state in the starting material is reduced in the presence of mauve to the chromium 1 plus or chromium 0 species which then carries out this catalytic function. Now, it was also possible to use chromium ACAC directly as a precursor and that makes the reaction fairly easy to handle in the laboratory. A very simple complex called DPPE which is the best diphenyl phosphino ethane which has got 2 phenyl groups on each phosphorous can also be used as a catalyst. Surprisingly that gives you significantly less activity, but the C8 selectivity is also poor. So, clearly the PNP ligand is a much better ligand if you want to synthesize the optin. So, it is now it is clear that the electronic effect of the PNP and also as we shall see in a minute the steric effect is an important factor. Now, these researches although I have shown you only 2 ligands these researches have applied a large library of PNP ligands as well some of them as exotic as a thynyl substituent on the phosphorous, but these substituents although the one that is pictured for you here is sufficiently reactive. It is not necessary to use this exotic ligand and the ligand that we saw earlier the bis diphenyl phosphino amine is itself quite useful for carrying out selective octamerization of the ethylene to produce octene. So, now we have seen that chromium which we had originally touted as a main metal which would do trimerization is useful for tetramerization. So, chromium was a classic trimerization metal. So, how is it that we are able to do tetramerization? So, more research has gone on in this area and a very recent paper published in the American chemical society journal called catalysis tells us about the selectivity between trimerization versus tetramerization. What they have shown is that the steric bulk on the ligand which we use. So, the PNP ligand that you have the steric bulk on this ligand is responsible for the selectivity between trimerization and tetramerization. The more bulky the ligand it is likely that will give you the tetramerization catalyst. So, not only electronics steric effects are also very important in order to decide between the trimerization or the tetramerization. So, far we have talked about trimerization, tetramerization and so on. We can also do reactions with multiple ends which means dienes and prions and variety of reactions are known, but the principles are the same. In order to do a coupling reaction you usually carry out an oxidative coupling reaction and that leads to the coupling of two dienes. Here I have shown you two dienes which can couple in a linear fashion. This is a linear product and this is a branched product. So, these dienes are not so readily available as the ethylene is. So, these reactions are less studied than the ethylene reactions that we have just discussed, but suffice it to say these reactions are also possible. Now, let us take a look at polymerization. Why is polymerization so important? Because the polymerization of ethylene to give you polyethylene is a very useful reaction polyethylene both low density polyethylene and high density polyethylene have got extensive industrial uses. So, it is important that we take some time and examine this particular process. Let me give you a brief history of the polymer catalysis and I have listed here a series of events that are critical for the polymerization for understanding polymerization history. First of all radical cationic and anionic polymerizations were known, but the molecular weights of the polymerized species were not as high as they were when Ziegler and Nata discovered metal catalysts in 1955. So, polyethylene and polypropylene were first discovered and made popular essentially in the 1950s until then only polymers which were not having high molecular weights were known and they were also not reproducibly made. What Ziegler and Nata discovered was that not only are the metals titanium zirconium group metals are important, they also showed that the support on which these catalysts are kept in this particular case I have shown you magnesium chloride and secondly the discovery of Mao. These things made a very big change in the catalysis industry. So, 1980s another very significant discovery was made and that was the fact that instead of using the group 4 transition metals one can also use metallocenes which could perform as single side catalysts when you suspend the catalysts on or support the catalysts on magnesium chloride the nature of the catalyst is not very clear. However, metallocene catalysts are single side catalysts meaning they have a well characterized structure and there is only one type of an active species. We will see how this makes a difference a little later. Then more recently in 1995 it was discovered that late transition metals can also do catalysis of ethylene. Let us proceed with Ziegler and Nata. We will not be talking about the properties of polymer but essentially the mechanisms of polymerization and how the metals play an important role in this polymer synthesis. So, Ziegler was the first one to show that polyethylene can be generated and very low pressures compared to what was done earlier that very low pressures they can be polymerized to generate useful polymeric materials. It was Nata who extended it to polypropylene and that made a very big change in the polymer industry. As a result of their 1955 discovery they were together awarded the Nobel Prize in 1963. Now you might be wondering what is so great about polymerization of ethylene or propylene and what are the advantages. There are significant advantages and disadvantages of the Ziegler Nata system and we will take a look at it in the following slides. First of all radical polymerization as I had mentioned earlier of ethylene requires a very high pressure of ethylene and it also required a high temperature and it led to significant amount of branching and the polymers that were made using these procedures were not very useful. But when Nata polymerized propylene which is what is shown here he obtained what is called isotactic polymers. Isotactic polymers are those where the where the alkyl groups are organized in same on the same side of the carbon in a polymer chain. I have pictured for you here the polymer chain which is as if it is in the plane of the screen. Then the methyl groups are going inside the screen whereas the hydrogen which is present here is coming towards you. So if you keep all the carbons in a plane then the methyl groups are going away from you and since all of them are going away from you is this called an isotactic polymer. Now this turns out that the polymer characteristics are very important and these are dependent on the way in which these polymers pack in the solid state and the way they pack depends on how these methyl groups are oriented. If they are isotactic they have excellent properties. So not only that the polymer molecular weights are very high it is about 10 power 5 to 10 power 6 Dalton's they have high density etcetera and all of these are significant advantages. Propylene polymerization was not even possible although ethylene could be polymerized propylene was not polymerizable at all and even if it was polymerized it generated polymers with not so clear stereochemistry. It would either be a syndiotactic which means they alternate the methyl groups alternate or they would be totally etactic which means they were randomly oriented along the polymer chain. Sometimes you can generate a metal complex which can give you stereo blocks but alternating but regular orientation of the methyl groups. All of these polymers they have different properties and so they are useful in their own right except when you have a random orientation in which case the usefulness decreases. So this was the most significant improvement that Nata made and now we ask the question why is the Nata catalyst so specific and how is it so active and at room temperature and low pressures how are we able to carry out polymerization so efficiently. Let us first look at the basic mechanism for polymerization it involves an extremely simple insertion reaction as opposed to the oxidative coupling that we have been talking about these are insertion reactions carried out on the titanium center. Now if you have a methyl group from the mauve or an alkyl group from the A L E T 3 which is usually used to activate the titanium you will have an alkyl group on the titanium in the place where I have marked it with a growing polymer chain. So in this position you will realize that you have this group which is attached to the titanium which can now undergo an insertion reaction and we will mark this insertion reaction like this. If this anionic group inserts into the ethylene and a new carbon titanium bond is formed you would get this particular product and that product has got a vacant site here this is a vacant site here that we have marked it with V and you have the growing polymer chain in the cis position. Now it is very easy to see that you can add an ethylene again into the vacant coordination site and the growing polymer chain can do another insertion reaction this time between this carbon and the alkene carbon like this and so the growing polymer chain now has got second ethylene attached to it. So we started out with a magenta carbon being attached to the titanium and we have added a blue ethylene just for the sake of identification I have color coded it. So we have added a blue ethylene and a red ethylene to the titanium. So you can have a very rapid polymerization of this ethylene notice that we are not changing the thermodynamics of this whole process. The thermodynamics is still in the same way as in the uncatalyzed process carbon carbon bond formation releases a lot of energy because you are converting a double bond to a single bond. But you lose entropy the net gain is the strong carbon carbon bond which leads to forward reaction polymerization is feasible in these cases. Now let us take a look now at stereo regularity. If you take propylene and if you look at the polymerization in the same catalytic cycle that we have just discussed you will notice that because these two groups are oriented in a cis position it is important to orient them away in such a way that the methyl group which is the bulky group on the propylene methyl group is the bulky group on the propylene. The growing polymer chain is the bulky group on the alkyl chain which is attached to the titanium both of them will have to be oriented away from each other. And because of this requirement you will always end up with the chain inserting in such a way that the methyl groups end up in the same position or in the same direction along the polymer chain because you want to always orient the methyl group away from the growing polymer chain. So this very simple fact and the fact that in the resting state of the catalyst this vacant site has a beta hydrogen interaction as a weak interaction with the beta hydrogen on the growing polymer chain you end up with a very strong stereo regularity in the polymerization process. Now it is been possible to have polymerization of ethylene with a variety of non groups for metals and this has led to a situation where you might call it the iron age of polymerization where even metals like iron have been activated using mauve again you need a reducing age with a large anion so that the iron is protected and only the ethylene is able to approach the metal center. And when you have ethylene coordinated to the iron and you can have insertion reaction and you can have oligomeric oligomerization of olefins to give you alpha olefins or high molecular weight polymers like HDP when you use these catalysts. So the mechanism of the reaction is assumed to be the same and it is because of these bulky groups that are present on the iron that approach of other anions which would poison the catalyst are prevented especially water will be a serious poison for the catalyst so that is prevented by the presence of a large excess of mauve. Now the chain growth is what needs to be very efficient in order to generate the polymer and this chain growth process as we have mentioned would be identical to what we showed on the titanium except that now you have the iron which is in the plus 1 oxidation state and it is undergoing an insertion reaction with the ethylene. But at the same time it has to compete with other processes which will stop the chain from growing what are these processes now you can see them in this slide that I have pictured for you here you have several processes instead of having insertion reaction you can have an exchange with simple ethylene which would regenerate the catalyst instead of continuing the polymer growth you can have an exchange reaction where ethylene comes in and the bulky polymer alpha olefin goes away so that is called an exchange reaction you can also have a reaction with trimethyl aluminum if you have trimethyl aluminum as a reducing agent then it tends to have a chain transfer reaction where a methyl group is transferred to the growing chain and the reaction stops and this is pictured here where once again a methyl iron bond is formed and the chain growth can continue but never the less you have stopped the main chain from growing at this particular point a third possibility is the beta hydrogen abstraction if beta hydrogen abstraction becomes more favorable than the alkene insertion then of course you would end up with a short polymer chain rather than a very long high molecular weight polymer in the whole reaction process. So, any polymerization catalyst has to compete with these two three possibilities so this is the chain growth mechanism that would favor high molecular weight and all these processes these three processes which I am labeling as one two and three these three have to compete with the polymerization process which is going on in the in the upward direction. So, this is usually favored by bulky groups on the metal atom which is coordinating to the ethylene and growth is favored when you have unfavorable energetics for the beta hydrogen abstraction. So, people have from the iron that I have just described to you it is also been possible to have nickel complexes and here is a nickel complex that is pictured once again you have a bulky ligand which is present on the metal that seems to be a key factor and methyl allomoxane is again a key factor that is necessary for reducing the nickel from the 2 plus state to the 0 plus state and it is possible to generate high molecular weight polymers using this particular catalyst as well. So, you can see that the principles are very similar to what is happening on the titanium titanium is not unique you need a low valent metal center which can carry out the polymerization very effectively, but it needs to be prevented from anions attacking the metal center and stopping the reaction. It not only 3 D metals here is an unusual example of a 4 D metal or a 4 D metal which is capable of carrying out this reaction. In this case very large tetra aryl borate anion has been used as a stabilizing anion to carry out this polymerization process and this polymerization is carried out at not too high pressures, but the main the important difference and advantage is that they have co polymerized 2 species in order to generate a very interesting polymer which is having the substituent on the polymer chain and this allows for speciality polymers to be synthesized. So, the polymer industry is in fact having a gamut of transition metals and metal complexes available for it to make very interesting polymers. Here is one more example where a palladium center has been used for generating alternating co polymer of carbon monoxide and ethylene. So, this generates polymer where the repeat unit has got CO and ethylene. So, the ethylene has come from these 2 carbon centers and carbon monoxide was also a reactant. So, you can make this high molecular weight thermoplastic using this palladium complex. Finally, we look at some of the products the early and properties of the early and late transition metals and the type of catalysts that have been used. The important point is to generate an active site that would not be blocked by an anion and in most cases, MOA was used as the very large blocking anion that is very weakly interacting with the metal center. So, you have a weakly or non coordinating species that is important for both centers. You can have soft ligands in the case of late transition metals, but you need an oxo group or an X minus on the titanium and the vanadium and the early group early transition metals which have to be activated with MOA and usually the coordination geometry around the early transition metals are tetrahedral whereas the late transition metals prefer a square planar intermediate. Now, the tolerance of functional groups is one place where the two differ very significantly. In the case of late transition metals, we can have tolerance of functional groups whereas in early transition metals only ethylene can be polymerized. Finally, I would end with a very recent example where a chromium catalyst has been used for synthesizing ultra high molecular weight polyethylene.