QSPR with TAU indices: Molar refractivity of diverse functional acyclic compounds

Molar refractivity of diverse functional acyclic compounds (n = 166) has been correlated with first order TAU indices to unravel the diagnostic feature of the TAU scheme. It has been found that TAU relations could satisfactorily explain the variances of the molar refractivity values of diverse functional compounds (up to 98.6% predicted variance and explained variance for the composite set of 166 compounds), especially when the first order composite topochemical index is partitioned into different components. Moreover, specific contributions of functionality, branching, shape and size terms to the molar refractivity values could be found out from the relations involving TAU parameters. It is observed that molar refractivity increases with the rise in molecular bulk. Further, branching has specific contribution on molar refraction depending on the type of ramification: it has negative contribution to molar refractivity for compounds with same molecular bulk. Negative impact of hydroxy, amino and oxy groups and positive impact of bromo and iodo functionalities on molar refraction are also observed. The predicted MR values based on a selected TAU model are also compared with the calculated MR values according to the Crippen's fragmentation method.