Multi-parameter correlations of solvent effects on kinetics of 1,3-dipolar cycloaddition reaction of C, N-diphenylnitrone with fumaronitrile: An experimental and theoretical study

1478-1484Solvent effects on kinetics of 1,3-dipolar cycloaddition reaction between C,N-diphenylnitrone and fumaronitrile have been studied spectrophotometrically at 65°C. Second-order rate constants of the reaction decrease with increasing normalized polarity parameter ( E ). Therefore, polarity of the reactants is higher than that of the activated complex of the reaction. Linear correlation of the logk2 vs E gives acceptable result (r = 0.978; s.e = 0.098; F1,14 = 310.54). Single-parameter correlations of log k2 vs π* (dipolarity/polarizability) and a (hydrogen-bond donor acidity) do not give satisfactory results; therefore, π* and α are not individually important factors in determining solvent effects on the reaction rate. Dual-parameter correlation of log k2 vs π* and α gives interesting result (r= 0.994; s.e = 0.056; F2,13 = 495.85). Dipolarity/polarizability and hydrogen-bond donor acidity of media have parallel effects on decreasing of the reaction rate; therefore, the reactants of reaction are stabilized via hydrogen-bonding and dipole-dipole interactions with solvent molecules major than the activated complex. The values of log k2 correlate well with three sets of theoretical (computational) molecular parameters using theoretical linear solvation energy relationship. The theoretical descriptors are calculated by two semiempirical methods (MNDO and AM1 algorithm) and one ab initio method (with 6-31 G* basis set). The correlation equations are physically reasonable and may be used as probes for solute-solvent interactions. Statistically, suggested multi-parameter correlation equation, in which the theoretical descriptors were calculated by MNDO algorithm, is better than the other equations

Correlation between vapour pressure of organic compounds and semiempirical theoretical descriptors

1504-1526A quantitative structure-property treatment of vapour pressure has been performed for a structurally wide variety of organic compounds using theoretical descriptors, which are calculated by semiempirical molecular orbital methods (MNDO and AM1 algorithm). From the eight theoretical descriptors, in model I, Mw (molecular weight), q+(the most positive charge of a hydrogen atom), ɛA and ɛB (the covalent acidity and basicity terms), π1 (polari zability term) and μ (dipole moment) have major effects on the vapour pressure. In the models, vapour pressure of the compounds decreases with increasing Mw, q+, ɛB, π1 and μ Effects of Mw and π1 on the vapour pressure arc higher than those of the other theoretical descriptors. The suggested multi-parameter equations are statistically acceptable (in model I: n = 246, r = 0.972, s.e = 0.259, F6.239 = 673.85 and in model II:n = 247, r = 0.973, s.e = 0.251 , F7.239 = 615.39)