The application of a new approach based on organic homo‐rank compounds and homologous compounds to the structure–property relationship study of mono‐substituted alkanes

The two conceptual systems of organic homologous compounds and homo‐rank compounds give insight into the influence of structures on the properties of mono‐substituted alkanes X_i–(CH₂)_j–H from the transverse (change of repeating unit number j of CH₂) and longitudinal (change of functional group X_i) perspectives, respectively. This paper aims to combine the organic homo‐rank compounds approach together with the homologous compounds approach to explore the property change rules of mono‐substituted alkanes involving various substituents. Firstly, based on the concept of organic homologous compounds, the properties of mono‐substituted straight‐chain alkane homologues were linearly correlated to the two‐thirds power of the number of carbon atoms (N^2/3) in alkyl, and regression equations such as Q = A + BN^2/3 were obtained. The regression coefficients A and B vary with different substituents X_i, so coefficients A and B were employed to characterize the structural information of substituent X_i. The structural features of alkyls (–(CH₂)_j–H, that is, –C_jH_2j+1) were described by the polarizability effect index (PEI_(R)) and vertex degree–distance index (VDI). Then based on four parameters A, B, PEI_(R), and VDI, quantitative structure–property relationship models were built for the boiling points (Bp) and refractive indexes (n_D) of each mono‐substituted alkane homo‐rank series, where j = 3–10 and the substituents X_i involve F, Cl, Br, I, NO₂, CN, NH₂, COOH, CHO, OH, SH, and NC. Good results indicate that the combination of an organic homo‐rank compounds method and a homologous compounds method has exhibited obvious advantages over traditional methods in the quantitative structure–property relationship study of mono‐substituted alkanes concerning various substituents. Copyright © 2015 John Wiley & Sons, Ltd.