IMPORTANCE OF NON-BONDED INTERACTIONS IN AMIDE STRUCTURES

Explanations for the variations of bond lengths and bond angles in terms of conjugation, hyperconjugation, hybridization and non-bonded repulsions have been reviewed. Non-bonded repulsion appeared to offer the best explanation for exceptionally long CC bonds in the ammonium salts of oxalic and oxamic acids. To apply a rigorous test to this theory, the various known amide structures were compared with theoretical structures obtained using Bartell's hard-sphere" model and within the limits of error extremely good agreement was obtained. From this it was inferred that non-bonded repulsions are of prime importance in determining molecular geometry and the influence of hybridization. conjugation or hyperconjugation would appear to be small. Conversely the degree of conjugation or hyperconjugation cannot be deduced from bond lengths. © 1968."