二氟亚烷基卡宾与甲醛环加成反应机理的理论研究

用二阶微扰理论研究单重态二氟亚烷基卡宾与甲醛发生的环加成反应机理,采用MP2/6-31G*方法计算了势能面上各驻点的构型参数、振动频率和能量.结果表明,单重态二氟亚烷基卡宾与甲醛的环加成反应主要有两种反应通道,通道1中,两个反应物经a,b和c三条反应途径生成三元环构型的产物P1,其中途径c是主反应途径,该途径有两步组成:(Ⅰ)二氟亚烷基卡宾与甲醛生成了1个富能中间体(INT1c),是无势垒放热反应,放出能量为219.18kJ/mol;(Ⅱ)中间体(INT1c)异构化为产物二氟亚烷基环氧乙烷,其势垒为134.71kJ/mol.通道2的反应途径由三步组成:(Ⅰ)反应物首先生成了1个富能中间体(INT1b),为无势垒的放热反应,放出的能量142.77kJ/mol;(Ⅱ)中间体(INT1b)异构化成另一中间体(INT2),其势垒为22.31kJ/mol;(Ⅲ)中间体(INT2)异构化成四元环构型产物P2,其势垒为11.98kJ/mol.

Theoretical Study on Mechanism of Cycloaddition Reaction Between Difluorovinylidene and Formaldehyde

The mechanism of cycloaddition between singlet difluoro-vinylidene and formaldehyde was investigated with MP2/6-31G* method, including geometry optimization, vibrational analysis, and energetics for the involved stationary points on the potential energy surface. The results show that the title reaction has two major channels. The first one brings about a three-membered ring product(P1) via a, b and c paths, of which c is the leading path that consists of two steps: (Ⅰ) an intermediate (INT1c) is formed between difluoro vinylidene and formaldehyde through a free barrier exothermic reaction of 219.18 kJ/mol; (Ⅱ) the intermediate then isomerizes to a product, difluoro-methylene ethane oxide, with an energy barrier of 134.71 kJ/mol. The reaction path of channel 2 consists of three steps: (Ⅰ) an energy-rich intermediate (INT1b) is firstly formed between difluoro-vinylidene and formaldehyde through a free barrier exothermic reaction of 142.77 kJ/mol; (Ⅱ) the intermediate(INT1b) then isomerizes to the other one intermediate(INT2), with an energy barrier of 22.31 kJ/mol; (Ⅲ) the intermediate(INT2) isomerizes to one 4-membered ring products (P2), with an energy barrier of 11.98 kJ/mol.