14.4 : 羧酸衍生物的结构

Carboxylic acid derivatives contain an acyl group, such as CH₃CO, bonded to a heteroatom like Cl, O, or N.

The carbonyl carbon and oxygen are sp² hybridized, resulting in a trigonal planar geometry with bond angles approximating 120° and a carbon–oxygen bond length of 1.21 Å.

The derivatives are resonance stabilized, where the extent of stabilization depends on the electronegativity of the heteroatom.

Since nitrogen is less electronegative than chlorine or oxygen, it can readily donate its lone pair and accommodate the positive charge better, making amides the most stable.

The carbon–nitrogen bond in amides exhibits a partial double bond character, with the nitrogen atom being sp² hybridized and planar.

Consequently, in secondary and tertiary amides, rotation about the carbon–nitrogen bond gives E and Z conformers, where the equilibrium favors the less sterically hindered Z conformer.

Finally, in nitriles, both carbon and nitrogen are sp hybridized. They adopt a linear geometry where the carbon–nitrogen bond length is 1.16 Å.