丙二酸亚异丙酯衍生物的构象分析与分子集团结构适应理论

本文根据5-取代丙二酸亚异丙酯的核磁共振谱,利用“分子集团结构适应理论”观点,阐述了5-取代丙二酸亚异丙酯的构象,表明此化合物一般具有椅式构象;当取代基中含有芳基及羰基时,显示了这些基团对2-位甲基的远程屏蔽及远程去屏蔽效应,从而认为此时以船式构象存在。

THE CORRELATION BETWEEN THE CONFORMATIONAL ANALYSES OF THE5-SUBSTITUTED ISOPROPYLIDENE MALONATES AND THE PRINCIPLE OF THE STRUCTURAL ADAPTABILITY

In this paper, the conformation of the 5-substituted isopropylidene malonates was analyzed in detail according to the principle of the structural adaptability for the interreaction between the groups of molecules. The results agreed with their nuclear magnetic resonance spectra.(1) It was evident that the isopropylidene malonate had two energetically favoured chair conformations which could rapidly interconvert one another,(2) If the 5-substituted group contained aromatic group, such as phe-nyl, furfyl, the favoured conformation was that the aromatic ring tended to be parallel with the plane containing the two ester-groups. Here the boat conformation might be favourable. Therefore, the long range shielding effect of the aromatic ring toward the 2-methyl group could be shown. It means that the chemical shifts would move to higher magnetic field.(3) If the 5-substituted group was a carbonylmethyl group, the oxygen atom in carbonyl group approached to the three hydrogen atoms of the 2-methyl group. At that time a long range deshielding effect of the carbonyl group appeared.