They are chiral centers (such as asymmetric carbon atoms) and the double-bonded carbon atoms in cis-trans alkenes.
(e) The carbon bearing the SH group is not a stereocenter because two of its attachments (the methyl groups) are not different. Remember that and indicate position of atoms in space; their presence does not mean the atom is a stereocenter. Most instances of chiral molecules that you will encounter at this level of organic chemistry owe their chirality to the presence of one or more stereocenters. It is not necessary for a molecule to have a stereocenter to be chiral. Make models of the enantiomers of 2,3-pentadiene (1,3-dimethylallene) shown below. Having a stereocenter does not mean a molecule will always be chiral Also note attachments that differ only in conformation do not make a stereocenter. The only carbon of 2-butanol that bears 4 different attachments is the alcohol carbon. Example 2: Identify the stereocenter(s) in this molecule: Answer: Despite the wedges, this molecule has only one stereocenter, the alcohol carbon. Most instances of chiral molecules that you will encounter at this level of organic chemistry owe their chirality to the presence of one or more stereocenters. It is not necessary for a molecule to have a stereocenter to be chiral. Make models of the enantiomers of 2,3-pentadiene (1,3-dimethylallene) shown below. Having a stereocenter does not mean a molecule will always be chiral Stereocenter (chiral center): An atom with three or more attachments, interchanging of two of these attachments leads to another stereoisomer. Most commonly, but not limited to, an sp3 (tetrahedral) carbon atom bearing four different attachments.  Because stereocenters are the origin of chirality of most chiral organic molecules, it is useful to be able to recognize stereocenters within a molecule. Example 1: Identify the stereocenter(s) in this molecule: H 3 CClStereocenterH 3 CClNot a stereocenterCCCCH 3 HHH 3 CHO OHH HHOO OOHHOH. Most instances of chiral molecules that you will encounter at this level of organic chemistry owe their chirality to the presence of one or more stereocenters. It is not necessary for a molecule to have a stereocenter to be chiral. Make models of the enantiomers of 2,3-pentadiene (1,3-dimethylallene) shown below. Having a stereocenter does not mean a molecule will always be chiral A chiral carbon or asymmetric carbon is a carbon atom which is asymmetric. Most chiral molecules have a chiral carbon, though the presence of a chiral carbon does not necessarily make a molecule chiral (see meso compound). A chiral carbon is often denoted by C*. If the carbon is chiral, it follows that: 1  the carbon atom is sp 3 -hybridized; 2  there are four different groups attached to the carbon atom The most common stereocenters are chiral centers (such as asymmetric carbon atoms) and the double-bonded carbon atoms in cis-trans alkenes. A chiral center consists of an atom holding a set of ligands (atoms or groups of atoms) in a spatial arrangement which is not superposable on its mirror image. Most chiral molecules have a chiral carbon, though the presence of a chiral carbon does not necessarily make a molecule chiral (see meso compound). A chiral carbon is often denoted by C*. If the carbon is chiral, it follows that: 1  the carbon atom is sp 3 -hybridized; stereocenter. (organic chemistry). A (chiral) carbon atom that has four different substituents bonded to it. Also known as a stereogenic atom. 1  Facebook. 2  Twitter.  the carbons with the-Cl are chiral and stereocenters, the carbon with-cooh is only a stereocenter. The carbons with Cl-have 4 different groups, while the other carbon only has two groups (CHCHClCH2... and COOH).  Best Answer: A stereocenter or stereogenic center is an atom bearing groups such that an interchanging of any two groups leads to a stereoisomer. 
http://www.chem.ucla.edu/harding/tutorials/stereochem/id_stereocenter.pdf http://www.chem.ucla.edu/harding/tutorials/stereochem/id_stereocenter.pdf http://www.chem.ucla.edu/harding/IGOC/S/stereocenter.html http://www.chem.ucla.edu/harding/tutorials/stereochem/id_stereocenter.pdf https://en.wikipedia.org/wiki/Stereocenter https://en.wikipedia.org/wiki/Stereocenter http://encyclopedia2.thefreedictionary.com/Stereocenter http://forums.studentdoctor.net/threads/chiral-center-vs-sterocenter.595932/ https://ca.answers.yahoo.com/question/index?qid=20130925192801AAKVp3A
what is a stereocenter