Molecular Orbital Interpretation of Infrared Absorption Frequencies. II. α, β-Unsaturated Carbonyl, para-and meta-Substituted Aromatic Carbonyl Compounds, an Introduction of the Mutual Additive Substituent Parameter

Abstract

The infrared frequencies of α, β-unsaturated carbonyl compounds were correlated well with their π bond orders calculated by HMO method employing hetero-atomic parameters selected in the previous paper. Carbonyl frequencies of each group of para-substituted benzaldehydes, acetophenones and methylbenzoates were also shown to be in tolerable correlation with their π bond orders, respectively. But the regression lines of these three groups of compound run parallel separately. This phenomenon was considered to show a defect of conventional method of HMO calculation of disubstituted aromatic compounds [X-C6H4-Y]. As a method of improvement of this defect a series of mutual additive substituent parameter (MASP) was introduced. The MASP of substituent [X] is added to the coulomb integral of a hetero atom of substituent [Y], and vice versa. By use of MASP to aromatic compounds, carbonyl frequencies of not only saturated, α, β-unsaturated and para-, but also meta-substituted aromatic carbonyl compounds were all found to be linearly correlated with their π bond orders.