The reactions of carboxylic acids and carboxylic acid derivatives represent one of the classes of organic chemistry reactions that will play a prominent role in biochemistry. The acyl-substitution mechanisms are especially important, appearing in one form or another all over the place in biochemistry. Fatty acids, one of the most important precursors for several significant categories of biological lipids, are long-chain carboxylic acids. Fats, phospholipids and waxes are all fatty acid esters. Most naturally occurring fatty acids are unbranched and contain an even number of carbons.
Acetyl-CoA structure

Acetyl-CoA structure.