Batchelor R J, Green D F, Johnston B D, Patrick B O, Pinto B M
Department of Chemistry and Biochemistry, Simon Fraser University, Burnaby, BC, Canada.
Carbohydr Res. 2001 Feb 15;330(3):421-6. doi: 10.1016/s0008-6215(00)00304-9.
The conformational preferences about the C-N bond in N-(4-methoxyphenyl)-2,3,4,6-tetra-O-acetyl-alpha (1) and beta-D-glucopyranosylamine (2), in the solid state and in solution, have been investigated. The crystal structure of the axially substituted alpha anomer (1) indicates a conformational preference about the C-1-N bond in which nN-->sigmaC-O exo-anomeric interactions may be expressed, although this conformational preference is not displayed in solution. The solution conformation relieves steric interactions that result from expression of the exo-anomeric effect in the solid-state conformation. The conformational preference in the equatorially substituted beta anomer (2) both in solution and in the solid state is similar and permits expression of nN-->sigmaC-O exo-anomeric interactions. The structural data for 1 and 2 indicate significant differences in O-5-C-1-N-1 bond angles but insignificant differences in each of the O-5-C-1 or C-1-N-1 bond lengths. The J(C-1-H-1 coupling constants in 1 and 2 indicate a greater coupling constant for the alpha anomer that is consistent with a dominant nO-->sigma*C-H orbital interaction in the beta anomer that weakens the C-1-H-1 bond.
对 N-(4-甲氧基苯基)-2,3,4,6-四-O-乙酰基-α(1)和β-D-吡喃葡萄糖胺(2)中 C-N 键在固态和溶液中的构象偏好进行了研究。轴向取代的α异头物(1)的晶体结构表明了关于 C-1-N 键的构象偏好，其中可能存在 nN→σC-O 外端异头相互作用，尽管这种构象偏好在溶液中未表现出来。溶液构象缓解了固态构象中由于外端异头效应的表现而产生的空间相互作用。在溶液和固态中，赤道取代的β异头物(2)中的构象偏好相似，并且允许 nN→σC-O 外端异头相互作用的表现。1 和 2 的结构数据表明 O-5-C-1-N-1 键角存在显著差异，但 O-5-C-1 或 C-1-N-1 键长中的每一个差异不显著。1 和 2 中的 J(C-1-H-1)耦合常数表明α异头物的耦合常数更大，这与β异头物中占主导的 nO→σ*C-H 轨道相互作用一致，该相互作用削弱了 C-1-H-1 键。
