Group Contribution Model for Estimate of Correlation Energies of Linear Alkyl Alcohols

Abstract

The correlation energy contribution of a polar group in a molecular system was defined and the contributions of HO, CH 3 , and CH 2 groups in CH 3 (CH 2 ) m OH (m＝0-4) linear alkyl alcohols were calculated and studied at MP2-OPT2/6-311＋＋G(d) level. It is revealed that the E corr (HO) and E corr (CH 3 ) values of two terminal groups decrease somewhat with increase of number m in CH 3 (CH 2 ) m OH (m＝0-4) series. The value of E corr (CH 2 ) in the α position is larger than those values of methylene groups in other positions in the same system, and the farther the CH 2 from HO group in the molecule, the smaller the value of E corr (CH 2 ) in CH 3 (CH 2 ) m OH (m＝1-4) systems. Therefore, it was predicted that with the increase of number m in CH 3 (CH 2 ) m OH systems the values of E corr (CH 2 ) that are those of CH 2 groups relatively far from the terminal HO group would show a converging trend to that of a "standard" CH 2 group and its value of E corr (CH 2 ) would be transferable in CH 3 (CH 2 ) m OH homologous systems. The excellent fitting relationships between the total correlation energy and the number of (m-1) where m is the number of methylene groups were obtained from both results at MP2-OPT2/6-311＋＋G(d) level for CH 3 (CH 2 ) m OH (m＝ 2-4) systems by Meld program and at MP2/6-311＋＋G(d)//HF/6-311＋＋G(d) level for CH 3 (CH 2 ) m OH (m＝2-7) systems by Gaussian 98 program, which show that the total correlation energy is a linear function of the number of (m-1).