α-Epimerisation has been found to be absent in the reactions of threo-1,2-diphenyl-1-propyltrimethylammonium ion and its -2-d₁ analogue with t-butoxide ion in t-butyl alcohol at 30ºC. The formation of trans-α-methylstilbene, cis-α-methylstilbene and threo-N,N-dimthyl-1,2-diphenyl-1-propylamine has been associated with anti-elimination, syn-elimination and with nucleophilic substitution at a N-methyl carbon atom, respectively, and interpreted in terms of structural and medium features of the reactions. The β-hydrogen isotope effects for anti- and syn-elimination have been associated with reactant-like and product-like transition states, respectively, for these reaction modes. / Thesis / Master of Science (MSc)