线性氟代烷烃电子相关能的基团加和性

应用Meld 程序在MP2-OPT2/6-311++G(d)水平计算了线性氟代烷烃分子CH3(CH2)mF(m=0-5)中—CH3、—CH2—和—F基团电子相关能贡献值. 计算结果表明, 在CH3(CH2)mF(m=0-5)体系中, 端基—F、—CH3基团电子相关能贡献值Ecorr(—F)和Ecorr(—CH3)随着m的增大而逐渐减小. 分子中α位置—CH2—基团电子相关能贡献值Ecorr(—CH2—)大于其他位置的贡献值. 通过计算结果可以推断, 在CH3(CH2)mF体系中随着m的逐渐增大, 远离端基—F的—CH2—基团电子相关能贡献值逐渐减小并将趋于不变, 此—CH2—基团可看作一个标准的亚甲基且其Ecorr(—CH2—)的数值在CH3(CH2)mF体系中具有传递性. 应用Meld程序在MP2-OPT2/6-311++G(d)水平对CH3(CH2)mF(m=2-5)体系的计算结果和应用Gaussian 98程序在MP2/6-311++G(d)//HF/6-311++G(d)水平对CH3(CH2)mF(m=2-10)体系的计算结果均表明, 体系总电子相关能与体系中(m-1)数值呈线性关系.

Additivity of Group Contribution of Electron Correlation Energies in Linear Alkyl Fluorides

Correlation energy contributions of the —CH3, —CH2— and —F functional groups in linear alkyl fluorides CH3(CH2)mF (m=0-5) were calculated and studied at MP2-OPT2/6-311++G(d) level using Meld program. We found that with an increase in the number of intervening methylene groups in the studied systems, values of Ecorr(—F) and Ecorr(—CH3) decreased in the CH3(CH2)mF (m=0-5) series. Values of Ecorr(—CH2—) are different in different positions with respect to the —F group in the system. The value of Ecorr (—CH2—) for the α position is larger than the values for methylene groups in other positions within the same system. The farther the —CH2— is from the —F group in the molecule, the smaller the value of Ecorr(—CH2—) is in CH3(CH2)mF (m=1-5) systems. We predict that with an increase in the number m in the system, values of Ecorr (—CH2—), which are those of—CH2—groups relatively far fromthe terminal —F group, would converge to the value of a“standard”—CH2—group. This Ecorr(—CH2—) value is transferable between CH3(CH2)mF homologous systems. Results for CH3(CH2)mF (m=2-5) systems from Meld program at MP2-OPT2/6-311++G(d) level and results for CH3(CH2)mF (m=2-10) systems from Gaussian 98 program at MP2/6-311++G(d)//HF/6-311++G(d) level showthat the total correlation energy is a linear function of (m-1), where m is the number of methylene groups in the system.