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

Abstract

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 from the terminal —Fgroup,wouldconvergetothevalueofa"standard"—CH2—group.ThisEcorr(—CH2—) valueistransferablebetween 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 show that the total correlation energy is a linear function of(m-1) ,where m is the number of methylene groups in the system.