Ch21Su08

Ch21Su08 - Carboxylic Acid Derivatives Carboxylic...

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Carboxylic Acid Derivatives Carboxylic derivatives are described as compounds that can be converted to carboxylic acids via simple acidic or basic hydrolysis. The most important acid derivatives are esters, amides and nitriles, although acid halides and anhydrides are also derivatives (really activated forms of a carboxylic acid). Esters of Carboxylic Acids These are derivatives of carboxylic acids where the hydroxyl group is replaced by an alkoxy group. We have already seen that esters are produced via the reaction of an alcohol with a carboxylic acid. Nomenclature The names of esters are derived from the names of the compounds that are used to create them. The first word of the name comes from the alkyl group of the alcohol, and the second part comes from the carboxylate group of the acid used. E.g. 07db3939699405512f86cf2ef6b5b51008f11752.doc Page 1 R C X O R C O O R C O-R' O R C NH 2 O C O R R C N acid halide RCOX anhydride (RCO) 2 O ester RCO 2 R" amide RCONH 2 nitrile RCN R C O O-H R' O-H R C O O-R' + H 2 O H + CH 3 C O H-O H 3 C O-H CH 3 C O H 3 CO + H 2 O H + methanol ethanoic acid methyl ethanoate
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A cyclic ester is called a lactone, and IUPAC names of lactones are derived by adding the term lactone at the end of the name of the parent carboxylic acid it came from. E.g. Amides of Carboxylic Acids An amide is a composite of a carboxylic acid and an amine (or ammonia). Heating the salt formed when an amine and carboxylic acid react drives off the water produced, and an amide is formed. Amides are much less basic than their parent amines since the lone pair of electrons on Nitrogen are delocalized onto the carbonyl oxygen . In fact in strong acid, it is the oxygen that gets protonated first! 07db3939699405512f86cf2ef6b5b51008f11752.doc Page 2 H 2 C H 2 C C H 2 OH OH C O H 2 C H 2 C C H 2 O C O + H 2 O 4-hydroxybutanoic acid 4-hydroxybutanoic acid lactone R C O O-H R' NH 2 R C O NH-R' + H 2 O H +
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This conjugation means the N should be sp 2 hybridized, and indeed the amide nitrogen has a planar arrangement of bonds with bond angles close to 120°. The C-N bond has partial double bond character, and the rotational barrier is 18kcal/mol. Amides of the form R-CO-NH 2 are called primary amides since the nitrogen is only bound to one carbon atom (like R-NH 2 is primary). Amides that are of the form R-CO-NHR' are called secondary amides, or N- substituted amides. Amides of the form R-CO-NR 2 are tertiary amides, or N,N-disubstituted amides. Nomenclature of Amides To name a primary amide, identify the acid part and remove the -oic acid suffix and add -amide E.g. To name a secondary or tertiary amide, the alkyl groups on nitrogen are treated as substituents, and are given the prefix N (since they are the nitrogen). Cyclic amides are known as
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Ch21Su08 - Carboxylic Acid Derivatives Carboxylic...

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