BLYP and mPW1PW91 Calculated Structures and IR Spectra of the Stereoisomers of Tetra-O-methylsulfinylcalix[4]arene

Abstract

Molecular structures of the various conformers for the four stereoisomers of tetra-t-butyl-tetra-O-methylsulfinyl-calix[4]arene (1) were optimized using DFT BLYP and mPW1PW91/6-31G(d,p) (hybrid HF-DF) calculation methods. We have analyzed the total electronic and Gibbs free energies and normal vibrational frequencies of 16 different structures from four major conformations (cone (CONE), partial cone (PC), 1,2-alternate (1,2-A), 1,3-alternate (1,3-A)) of the four stereoisomers [1(rccc), 1(rcct), 1(rctt), 1(rtct)]. The mPW1PW91/6-31G(d,p) calculations suggested that the 1(rccc) CONE , 1(rcct) PC , 1(rctt) PC , and 1(rtct) 1,3-A were the most stable conformations of the respective stereoisomers. These outcomes are in accordance with the experimental structures obtained from X-ray crystallography. The electrostatic repulsion between the sulfinyl and methoxy groups is a primary factor for the relative stabilities of the four different conformations. The IR spectra ofthe most stable conformers [1(rccc) CONE , 1(rcct) PC , 1(rctt) PC , 1(rtct) 1,3-A ] of each stereoisomer were compared to each other.