硼氢化反应机理(Ⅰ):HCN+BH_3反应的反应途径

Reaction Mechanism of Hydroboration(Ⅰ):Reaction Ergodography for the HCH + BH_3 Reaction

利用量子化学从头计算法RHF／4-31G基组对氢氰酸的硼氢化反应进行了理论研究．IRC分析表明：氢氰酸与甲硼烷通过“类四中心”过渡态，直接加成生成产物．排除了另两种反应机理的可能性：（1）甲硼烷直接进攻碳-氮π键，经三中心过渡态生成产物；（2）首先形成直线型分子复合物。

The ab initio calculation have been performed for the hydroboration reactions of hydrocyahic acid at 4-31 G basis set. The results indicate that the reaction proceeds exother-mally, with an activation barrier of 145. 791 kJ/mol. In the gas phase, the reaction is shown to proceed in one stages: the addition reaction of hydrocyanic acid with boranc proceed to the product through a quasi-four-centre transition state. The possibility of other mechanisms, involving the direct attack of the carbon-nitrogen π-bonding by borane, resulting in a threecentre transition state, and the formation of the linear complex and its rearrangement to the product via intramolecular hydrogen migration, have been eliminated.