Thesis (M.Sc.)--Chulalongkorn University, 2006

Conversion reactions of 2,3-dimethyl-2,3-butanediol (DMBDOL) to 2,3-dimethyl-1,3-butadiene (DMBDENE) and 2,3-dimethyl-2,3-pentanediol (DMPDOL) to 2,3-dimethyl-1,3-pentadiene (DMPDENE) in acid-catalyzed system have been investigated using density functional theory method at B3LYP/6-31G(d) and B3LYP/6-311+G(d,p) levels of theory. Activation energies of conversion reaction of 2,3-dimethyl-2,3-butanediol (DMBDOL) and 2,3-dimethyl-2,3-butanediol with molecule of water in acid-catalyzed systems are 55.13(60.17) and 26.21(30.42) kcal/mol, respectively. The activation energy of conversion reaction of 2,3-dimethyl-2,3-pentanediol (DMPDOL) and 2,3-dimethyl-2,3-pentanediol with molecule of water in acid-catalyzed systems is 69.74(67.15) and 20.12(29.05) kcal/mol, respectively (method B3LYP/6-31G(d) is in the parenthesis). The activation energy of the conversion reaction of 2,3-dimethyl-2,3-butanediol and 2,3-dimethyl-2,3-pentanediol are decreased when the water molecule was added. The water molecule is sufficient to affect protonation, can acts as a base to remove the adjacent protons from intermediates.