Structure and thermochemistry of disulfide-oxygen species

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 SO_2, which is formed by oxidation of sulfur hydrocarbons and H_2S. This study describes the structure, internal rotor potentials, bond energies and determines thermochemical properties ([Delta]_fH , S and Cp(T)) on the S-S bridge system in the sulfur bridged molecules CH_3SSOH, CH_3SS(=O)H, HSSOH, HSS(=O)H and CH_3SSOCH_3 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 CH_3SSOH, CH_3SS(=O)H, CH_3SS=O and CH_2SSOH are -38.46, -17.74. -17.02 and 7.17 kcal mol^{-1} respectively. The C--H Bond Energy of CH_3SSOH 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 CH_3SSOH parent undergoes electron rearrangement upon loss of the CH_3SSO--H hydrogen atom to form the more stable CH_3SS=0 structure. The C--H bond energy of CH_3SS(=O)H is remarkabix weak at only 77.01 kcal mol^{-1}' and results in the formation of CH_2SSOH radical by the loss of H--CH_2SS(=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 CH_3SS(=O)--H hydrogen atom forms a CH_3SS=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 CH_3SSOCH_3 and the radical CH_2SSOCH_3 are -34.33 kcal mol-l and 11.4 kcal mol-l respectively. It is important to note that as the CH_3SSOCH_2 radical is formed it immediately dissociates to lower energy products CH_3SS(=O) + CH_2=O with no significant LT 6 kcal mol-l) barriers. This CH_3SSOCH_2; radical does not exist.

Name thesis:degree_name

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

Discipline thesis:degree_discipline

Chemistry and Environmental Science

Year

2008

Author dc:creator

• Pillai, Shyamala Pravin

Contributors dc:contributor

• Joseph W. Bozzelli
• Carol A. Venanzi
• Tamara M. Gund

• S-S bridge system
• Sulfer bridged molecules
• Thermochemistry
• Disulfide-oxygen
• Chemistry

Repository record dc:identifier

https://digitalcommons.njit.edu/theses/335

OAI identifier oai:identifier

oai:digitalcommons.njit.edu:theses-1334