Quantum Chemical Analysis of Thermodynamics of 2D Cluster Formation of n-Thioalcohols at the Air/Water Interface

Abstract

The semiempirical PM3 method is used to calculate the thermodynamic parameters of the formation of monomers, dimers, trimers, tetramers, and one of the possible hexamers of saturated thioalcohols with normal structure and alkyl chain lengths of 6−16 carbon atoms. The dependencies of the potential energy surfaces on the torsion angles for monomers and dimers of normal thioalcohols are calculated. The most stable conformations of monomers and dimers are determined and used to construct the structures of trimers, tetramers, and larger clusters. For various conformations of dimers, trimers, tetramers, and for the hexamer, the thermodynamic parameters of clusterization (enthalpy, entropy, and Gibbs energy) are calculated. It is found that these parameters are stepwise-dependent on the alkyl chain length. It is shown that a two-dimensional square-symmetric infinite cluster and clusters constructed on the basis of cyclic trimers are formed for alkyl chain lengths of 14−15 carbon atoms and above.