Studies of the Structure, Amidicity, and Reactivity of N-Chlorohydroxamic Esters and N-Chloro-β,β-dialkylhydrazides: Anomeric Amides with Low Resonance Energies

Abstract

Density functional calculations have been carried out to determine the properties of the title anomeric amides. At the B3LYP/6-31G(d) level, 'N'-chloro-'N'-methoxyacetamide 8a is computed to be strongly pyramidal at nitrogen with a long amide bond that is untwisted. 'N' Chloro-'N'-dimethylaminoacetamide 9a is completely planar, but its amide bond is still much longer than that in 'N','N'-dimethylacetamide 4. This is a steric, rather than a resonance, effect. COSNAR and a trans-amidation method calculate low resonance energies for both model amides, which is attributed to the combined electronegativity of the heteroatoms at the amide nitrogen and the strong anomeric effect when there is a chlorine substituent on nitrogen. When M06 and ωB97X-D dispersion-corrected density functional methods are used with the expanded 6-311++G(d,p) basis set, the resonance energies of 8a (-34 kJ mol-1) and 9a (-49 kJ mol-1) are in line with the gross electronegativity of the substituent atoms. Unlike other anomeric amides, 8a and 9a are not predicted to undergo HERON reactivity.