Estimating enthalpies of formation of monoalkenes by the bonding orbital-connecting matrix of molecular graphics and the steric effect of the cis/trans configuration

The bond orbital-connecting matrix method was developed to estimate the enthalpies of formation for monoalkenes, in which the chemical environment of each bond in a molecule can be distinguished from each other and the relative bond energy can be calculated. A rational semiempirical method was provided for quantifying the π bond energy and a novel descriptor SZ/E was suggested to scale the steric effect of the cis/trans configuration in the monoalkene. Using the newly proposed parameters X1π and SZ/E together with ΣX1CC and ΣX1CH reported by our previous work (C. Cao, H. Yuan, A new approach of evaluating bond dissociation energy from eigenvalue of bonding orbital-connecting matrix for C-C and C-H bonds in alkane, J. Chem. Inf. Comput. Sci. 43 (2003) 600-608.), a modified bond additivity model was proposed for estimating the enthalpies of formation of monoalkenes:ΔfH0(monoalkene)=aNC-C+bΣX1CC+cNC-H+dΣX1CH+eΣSij+fX1π+gX1πSZ/E+hX1π/(ΣX1CC+ΣX1CH)where Sij denotes the steric effect of a C-C bond, X1CC and X1CH are the eigenvalues of the C-C and C-H σ bond orbital-connecting matrices, respectively. X1π is the eigenvalue of the π bond orbital-connecting matrix. The predictive ability of the model was examined by the leave-one-out (LOO) cross validation method. Not only can this modified bond additivity method be used to evaluate the enthalpies of formation for monoalkenes well, but also this method can be expected to estimate the enthalpies of formation for the high diversity of chemical compounds, which are under investigating in our team. This paper opens a new insight and may explore another way for the bond additivity method.