Organic Chemistry/Carboxylic acid derivatives The carboxyl group (abbreviated -CO2H or -COOH) is one of the most widely occurring functional groups in chemistry as well as biochemistry. The carboxyl group of a large family of related compounds called Acyl compounds or Carboxylic Acid Derivatives. All the reactions and compounds covered in this section will yield Carboxylic Acids on hydrolysis, and thus are known as Carboxylic Acid Derivatives. Hydrolysis is one example of Nucleophilic Acyl Substitution, which is a very important two step mechanism that is common in all reactions that will be covered here. Structure This group of compounds also contains a carbonyl group, but now there is an electronegative atom (oxygen, nitrogen, or a halogen) attached to the carbonyl carbon. This difference in structure leads to a major change in reactivity. Nomenclature The systematic IUPAC nomenclature for carboxylic acid derivatives is different for the various compounds which are in this vast category, but each is based upon the name of the carboxylic acid closest to the derivative in structure. Each type is discussed individually below. Acyl Groups Acyl groups are named by stripping the -ic acid of the corresponding carboxylic acid and replacing it with -yl. EXAMPLE: CH3COOH = acetic acid CH3COO-R = acetyl-R Acyl Halides Simply add the name of the attached halide to the end of the acyl group. EXAMPLE: CH3COOH = acetic acid CH3COBr = acetyl bromide Carboxylic Acid Anhydrides A carboxylic acid anhydride ([RC=O]O[O=CR]) is a carboxylic acid (COOH) that has an acyl group (RC=O) attached to its oxygen instead of a hydrogen. If both acyl groups are the same, then it is simply the name of the carboxylic acid with the word acid replaced with anhydride. If the acyl groups are different, then they are named in alphabetical order in the same way, with anhydride replacing acid. EXAMPLE: CH3COOH = acetic acid CH3CO-O-OCCH3 = Ethanoic Anhydride Esters Esters are created when the hydrogen on a carboxylic acid is replaced by an alkyl group. Esters are known for their pleseant, fruity smell and taste, and they are often found in both natural and artificial flavors. Esters (RCOOR1) are named as alkyl alkanoates. The alkyl group directly attached to the oxygen is named first, followed by the acyl group, with -ate replacing -yl of the acyl group. EXAMPLE: CH3COOH = acetic acid CH3COOCH2CH2CH2CH3 = acetyl butanoate cooh 1 cooh 1 2-ethan oic acid Amides Amides which have an amino group (-NH2) attached to a carbonyl group (RC=O) are named by replacing the -oic acid or -ic acid of the corresponding carboxylic acid with -amide. EXAMPLE: CH3COOH = acetic acid CH3CONH2 = acetamide Nitriles Nitriles (RCN) can be viewed a nitrogen analogue of a carbonyl and are known for their strong electron withdrawing nature and toxicity. Nitriles are named by adding the suffix -nitrile to the longest hydrocarbon chain (including the carbon of the cyano group). It can also be named by replacing the -ic acid or -oic acid of their corresponding carboxylic acids with -onitrile. Functional class IUPAC nomenclature may also be used in the form of alkyl cyanides. EXAMPLE: CH3CH2CH2CH2CN = butonitrile or butyl cyanide
Posted on: Wed, 05 Jun 2013 17:13:06 +0000
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