Department of Chemistry, School of Science and Technology, University of New England, Armidale, NSW 2351, Australia.
J Org Chem. 2011 Dec 2;76(23):9757-63. doi: 10.1021/jo201856u. Epub 2011 Nov 7.
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.
已经获得了两种糖端 N,N-二烷氧基酰胺（2 和 3）的首个 X 射线结构，证实它们在氮原子上具有极高的金字塔化程度，并且具有长的 N-CO 键，这是其他糖端酰胺的特征，也是酰胺性大大降低的结果。晶体在固态中也表现出酰胺氮的手性。使用 N,N-二甲氧基乙酰胺作为模型的密度泛函计算很好地预测了这些结构。通过两种独立的方法，COSANR 和一种新的转酰胺化方法，估计了 N,N-二甲氧基乙酰胺的酰胺性，得到的共振稳定能几乎相同，为-8.6 kcal mol(-1)，仅为在相同水平计算得到的 N,N-二甲基乙酰胺的 47%。总失稳由共振和诱导贡献组成，我们已分别对其进行了评估。氮上的电负性氧负责将氮孤对定位在酰胺氮上，这一因素导致共振的损失超过氮的金字塔化的影响，以及 N,N-二甲氧基乙酰胺预测优先在羰基氧上质子化而不是氮上质子化。
