The mechanism of 1,2-hydride shift in protosteryl C(20) cation (1A) and in dammarenyl C(20) cation (2A) was investigated by the semi-empirical AM1 method and ab initio quantum Chemical calculations (HF/3-21G level). Stationary points 1A/1B and 2A/2B, and the corresponding transition hydrido-bridged structures 1TS and 2TS were located on the energy surface. Process 1A→1B turned out to be energetically more favorable than process 2A→2B by ca. 9 kcal mol-1, mostly due to the unfavorable steric repulsive interaction between the methyl group at C(14) and the β-oriented side chain at C(17) in 1A and the lack of CC-hyperconjugative stabilization in 1A. The exothermicity of processes 1A→1B and 2A→2B was increased by subsequent introduction of substituents (H, Me, i-Pr, and t-Bu) at C(14). The more pronounced trend in 1A→1B proves that the origin of the relative stability of 1B comes from the steric interactions in 1A. Introduction of the halogen atom (F, Cl, and Br), due to its -I effect and relatively small size, changed the direction of the equilibrium 1AY/1BY, and 1AY was found to be by ca. 3 kcal mol-1 more stable than 1BY