摘要
本文用量子化学方法ＭＮＤＯ研究了没食子酸和它的甲酯、乙酯、雨酯、异丙酯、丁酯和叔丁酯的自由基的结构和自旋密度的关系以及自由基的相对稳定性．计算得出溶液中的分子构型的特点是：酯基ＲＣＨ２－ＯＣＯ－处于苯环的上方，酯基上的α氢原子的自旋密度因电子相关作用而增大．计算结果解释了它们的乙醇溶液的ＥＳＲ偶合常数的比值和分裂峰数．
Free radicals of 3, 4, 5-triliydroxylbenzoic acid (GA) and its methyl (MG), ethyl (EG),propyl (PG), iso-propyl (iso-PG), butyl (BG),and tertbutyl (t-BG) esters are investigated with MNDOcalculations. They are identitied by calculating the formation heat of the radicals using RHF and UHFthat are in the three hydroxyl groups. The 4th-postition one(peraposition) is eaSier to de-hydrogen andbe converted to radiccals than the other two. The 4th-position dehydrogen radicals are more stable withabout 4～10keals/mole. The electron densities of O13 and O14 are - 0. 354 and -- 0. 2963 respectively in the carboxylic group -C=O13-O14-H of GA. However, when converted to ester group C=O13-O14-R, the electron density of O14 is larger than that of O13. they are, there are more pzelectrons transfered to the three OH-oxygen atoms and benzene ring, then the contributions of the pz ofO13 to the 3-MO are weakened. As a result, the oher group's plane can be rotated more easily, andthe α-hydrogens can have more opPOrtUnity to approach the upper part of the benzene plane. Due tothe electron correlations, their spin densities are increased. The ESR resultS can then be explained.
基金
国家自然科学基金
中国科技术大学基金
关键词
量子化学计算
没食子酸酯
游离基
free radicals, callic acid, quantum chemistry MNDO
