Structures of N,N-Dialkoxyamides: Pyramidal Anomeric Amides with Low Amidicity

Author(s)
Glover, Stephen
White, Jonathan M
Rosser, Adam Andrew
Digianantonio, Katherine M
Publication Date
2011
Abstract
The first X-ray structures of two anomeric N,N-dialkoxyamides (2 and 3) have been obtained, which confirm that they are highly pyramidalized at nitrogen and have long N-CO bonds, a characteristic of other anomeric amides and a consequence of drastically reduced amidicity. The crystals also demonstrate chirality at the amide nitrogen in the solid state. The structures are well-predicted by density functional calculations using N,N-dimethoxyacetamide as a model. The amidicity of N,N-dimethoxyacetamide has been estimated by two independent methods, COSNAR and a new transamidation method, which give almost identical resonance stabilization energies of -8.6 kcal mol⁻¹ and only 47% that of N,N-dimethylacetamide computed at the same level. The total destabilization is composed of a resonance and an inductive contribution, which we have evaluated separately. The electronegative oxygens at nitrogen are responsible for localization of the nitrogen lone pair on the amide nitrogen, a factor that contributes to a loss of resonance over and above the impact of pyramidalization at nitrogen, as well as the fact that N,N-dimethoxyacetamide is predicted to protonate on the carbonyl oxygen in preference to nitrogen.
Citation
The Journal of Organic Chemistry, 76(23), p. 9757-9763
ISSN
1520-6904
0022-3263
Link
Publisher
American Chemical Society
Title
Structures of N,N-Dialkoxyamides: Pyramidal Anomeric Amides with Low Amidicity
Type of document
Journal Article
Entity Type
Publication

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