The iodoform test indicates the presence of an aldehyde or ketone in which one of the groups directly attached to the carbonyl carbon is a methyl group. Such a ketone is called a methyl ketone.
Ethanal is the only aldehyde to give the triiodomethane (iodoform) reaction. If Ris a hydrocarbon group, then you have a ketone. Lots of ketones give this reaction, but those that do all have a methyl group on one side of the carbon-oxygen double bond. These are known as methyl ketones. Equations for the triiodomethane (iodoform) reaction We will take the reagents as being iodine and sodium hydroxide solution. The chemistry of the triiodomethane (iodoform) reaction. What the triiodomethane (iodoform) reaction shows. A positive result-the pale yellow precipitate of triiodomethane (iodoform) - is given by an aldehyde or ketone containing the grouping: R can be a hydrogen atom or a hydrocarbon group (for example, an alkyl group). Lots of ketones give this reaction, but those that do all have a methyl group on one side of the carbon-oxygen double bond. These are known as methyl ketones. Equations for the triiodomethane (iodoform) reaction We will take the reagents as being iodine and sodium hydroxide solution. The reaction of iodine and base with methyl ketones is so reliable that the  iodoform test  (the appearance of a yellow precipitate) is used to probe the presence of a methyl ketone. It is synthesized in the haloform reaction by the reaction of iodine and sodium hydroxide with any one of these four kinds of organic compounds: (i) a methyl ketone: CH 3 COR, acetaldehyde (CH 3 CHO), ethanol (CH 3 CH 2 OH), and certain secondary alcohols (CH 3 CHROH, where R is an alkyl or aryl group). Chemistry of iodoform test is: Secondary alcohols also give positive iodoform test because during the reaction conditions, it gets oxidized to a methyl ketone. 9 people found this useful.  When iodine and sodium hydroxide are used as the reagents, a positive reaction gives iodoform. Iodoform (CHI 3) is a pale-yellow substance. Due to its high molar mass caused by the three iodine atoms, it is solid at room temperature (cf. chloroform and bromoform).  Iodoform is the organoiodine compound with the formula C H I 3. A pale yellow, crystalline, volatile substance, it has a penetrating odor (in older chemistry texts, the smell is sometimes referred to as the smell of hospitals) and, analogous to chloroform, sweetish taste. It is occasionally used as a disinfectant. It is synthesized in the haloform reaction by the reaction of iodine and sodium hydroxide with any one of these four kinds of organic compounds: (i) a methyl ketone: CH 3 COR, acetaldehyde (CH 3 CHO), ethanol (CH 3 CH 2 OH), and certain secondary alcohols (CH 3 CHROH, where R is an alkyl or aryl group). Iodoform Reaction. The iodoform test indicates the presence of an aldehyde or ketone in which one of the groups directly attached to the carbonyl carbon is a methyl group. Such a ketone is called a methyl ketone. In the iodoform test, the unknown is allowed to react with a mixture of iodine and base. Hydrogens alpha to a carbonyl group are acidic and will react with base to form the anion, which then reacts with iodine to form an alpha-iodo ketone. The iodoform test or iodoform reaction is a qualitative chemical test for the detection of ketones and aldehydes carrying an alpha methyl group. The reagents are iodine and sodium hydroxide. Only methyl ketones, or alcohols with the feature: CH3CH(OH)-R may undergo this reaction. Report Abuse. -The iodoform test or reaction is a chemical reaction where iodoform (CHI3) is produced by the multiple halogenation of a methyl ketone (a molecule containing the R-CO-CH3 group) in the presence of a base. R may be H, alkyl or aryl. The reaction can be used to produce CHCl3, CHBr3 or CHI3 The iodoform test or iodoform reaction is a qualitative chemical test for the detection of ketones and aldehydes carrying an alpha methyl group. The reagents are iodine and sodium hydroxide. Only methyl ketones, or alcohols with the feature: CH3CH(OH)-R may undergo this reaction. There are three steps to the iodoform reaction when starting from an alcohol. If the reaction starts from a methyl ketone, the first step is not needed.
http://www.chemguide.co.uk/organicprops/carbonyls/iodoform.html http://www.chemguide.co.uk/organicprops/carbonyls/iodoform.html https://en.wikipedia.org/wiki/Iodoform http://www.answers.com/Q/What_is_a_negative_iodoform_test https://en.wikipedia.org/wiki/Haloform_reaction https://en.wikipedia.org/wiki/Iodoform http://www.chem.umass.edu/~samal/269/aak.pdf https://in.answers.yahoo.com/question/index?qid=20071023102326AAsfaJw https://in.answers.yahoo.com/question/index?qid=20080121000829AA0vbAE
what does iodoform test indicate