(98l) Thermochemical Properties (Enthalpy, Entropy and Heat Capacity), Rotation Barriers, Bond Energies of Ch3sch2ch=O, Ch3sc(Ch3)=O, Ch3sch=O, Hsc(Ch3)=O, Hsch2c(Ch3)=O, Hsch=O, Hsch2ch=O and Ch3sch2c(Ch3)=O

David N. Nare, Shyam G. Patel and Joseph W. Bozzelli* Department of Chemical Engineering and Chemistry New Jersey Institute of Technology, Newark, NJ 07102, USA *Bozzelli@njit.edu, Phone (973)-596-5294; Fax: (973)-596-3586

Abstract

This study uses computational chemistry and Density Functional Theory to obtain thermochemical properties of acetyl mercaptans and sulfides. Structures, enthalpy (?xfHo298), enthropy (So298) and heat capacity [Cp(T)] are determined for several compounds using the density functional B3LYP/6-311G(d,p) level of calculation in the Gaussian 03 program suite. In this study, results from density functional B3LYP/6-311G(d,p) calculations in conjunction with three isodesmic working reactions are used to determine standard enthalpies of formation (?xfHo298) of sulfur-containing species using a set of known radical and stable species. Geometric structures, enthalpy (?xfHo298), entropy (So298) and heat capacity [Cp(T)] are also calculated at the same level. Total translational, vibrational and external rotation contribution to S and Cp(T) was calculated with "SMCPS", a program that combines vibration, translation, and external rotational contributions in a rigid-rotor-harmonic oscillator approximation based on structures and vibrational frequencies obtained from the density functional analysis. Contributions to entropy (So298) and heat capacity [Cp(T)] from internal rotations is also included. The average calculated ?xfHo298 are as follows: CH3SCH2CH=O =-35.22 °" 0.38 kcal mole-1; CH3SC(CH3)=O =-48.46 °" 0.58 kcal mole-1; CH3SCH=O =-38.03 °" 0.06 kcal mole-1; HSC(CH3)=O =-42.68 °" 0.21 kcal mole-1; HSCH2C(CH3)=O = kcal mole-1; HSCH=O =-29.44 °" 0.35 kcal mole-1; HSCH2CH=O =-27.76 °" 0.8 kcal mole-1; CH3SCH2C(CH3)=O =-47.51 °" 1.44 kcal mole-1.