Ab initio calculation of entropy and heat capacity of gas-phase n-alkanes with hetero-elements O and S:: Ethers/alcohols and sulfides/thiols

In this paper, the performance of the one-dimensional hindered rotor approach (ID-HR) is evaluated for n-alkanes with hetero-elements O or S. The internal rotations in these molecules show a behavior distinct from those in n-alkanes, for which 1D-HR is a cost-efficient method to describe the thermochemical features (entropy and heat capacity). It turns out that also for ethers, alcohols, sulfides and thiols this approach gives a satisfactory experimental agreement. This work confirms earlier results, and consolidates the assumption that the 1D-HR model is highly suitable for reproducing thermodynamic properties of single chain molecules, and that multi-dimensional. coupled hindered rotor approaches (nD-HR) are not necessarily required for attaining high accuracy. Moreover, it seems that the ID-HR results are almost independent of the details of the level of theory. (c) 2006 Elsevier B.V. All rights reserved.