Date of Award

Fall 2007

Document Type

Thesis

Degree Name

Master of Science in Chemistry - (M.S.)

Department

Chemistry and Environmental Science

First Advisor

Joseph W. Bozzelli

Second Advisor

Carol A. Venanzi

Third Advisor

Tamara M. Gund

Abstract

Sulfur compounds are known to form aerosols that can counteract the greenhouse effect, and recent studies suggest that aerosols can also contribute to global warming; sulfur species are also known as major contributors to acid rain. Both of these atmospheric chemistry interactions involve SO2, which is formed by oxidation of sulfur hydrocarbons and H2S. This study describes the structure, internal rotor potentials, bond energies and determines thermochemical properties (ΔfH°, S° and Cp(T)) on the S-S bridge system in the sulfur bridged molecules CH3SSOH, CH3SS(=O)H, HSSOH, HSS(=O)H and CH3SSOCH3 and the their radicals corresponding to H atom loss. Structure and thermochemical parameters (S° and Cp(T)) are determined using Density Functional B3LYP/6-31G (d, p), B3LYP/6-311++G (3df, 2p) and composite CBS-QB3 ab initio computational chemistry calculations.

Enthalpies of formation for CH3SSOH, CH3SS(=O)H, CH3SS=O and CH2SSOH are -38.46, -17.74. -17.02 and 7.17 kcal mol-1 respectively. The C--H Bond Energy of CH3SSOH is 97.73 kcal mol-1 , and the O-H bond energy is weak at 73.54 kcal mol-1 . The weak O--H bond results because the CH3SSOH parent undergoes electron rearrangement upon loss of the CH3SSO--H hydrogen atom to form the more stable CH3SS=0 structure. The C--H bond energy of CH3SS(=O)H is remarkabix weak at only 77.01 kcal mol-1' and results in the formation of CH2SSOH radical by the loss of H--CH2SS(=O)H hydrogen atom, and the S-H bond energy is also weak. The very weak S--H bond (only 52.82 kcal mol-1) formed from loss of the CH3SS(=O)--H hydrogen atom forms a CH3SS=O radical.

Enthalpies of formation for HSSOH, HSS(=O)H, HSS=O and SSOH are 33.62(+/-0.2) kcal mol-1 , -12.88 (+/-0.2) kcal mol-1 , -14.44 (+/-0.2) kcal mol-1 and - 19.96 (+/-0.2) kcal mol-1 respectively. The S--H Bond Energy of HSSOH is 65.76 kcal mol-1 , and the O-H bond energy is 71.28 kcal mol-1. The S--H Bond Energy of H--SS(=O)H is weak at only 45.02 kcal mol-1 and results in the formation of SSOH radical by the loss of hydrogen atom, and the S-H bond energy of HSS(=O)--H is very weak at 50.54 kcal mol-1. The very weak S--H bond, upon loss of the HSS(=O)--H hydrogen atom forms a more stable HSS=O radical.

Enthalpies of formation for CH3SSOCH3 and the radical CH2SSOCH3 are -34.33 kcal mol-l and 11.4 kcal mol-l respectively. It is important to note that as the CH3SSOCH2 radical is formed it immediately dissociates to lower energy products CH3SS(=O) + CH2=O with no significant LT 6 kcal mol-l) barriers. This CH3SSOCH2; radical does not exist.

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