Abstract
The neopentyl and the pinacol rearrangements as examples of Wagner–Meerwein rearrangements were investigated by the use of DFT calculations. As the first reaction, a model of neopentyl chloride (1b) and (H~2~O)~12~ was employed. In the reaction, the patterns of CCl scission, methyl migration, and COH formation were analyzed. The calculations have shown that the 2‐methyl‐2‐butanol (6) is formed in two steps with the transient intermediate, neopentyl alcohol (3). The first step is the nucleophilic substitution reaction and is the rate‐determining one. The second step is the dual migration of methyl and OH~2~ groups. The primary and tertiary carbocations were calculated to be absent in the neopentyl rearrangement starting from the hydrolysis. As the second reaction, the pinacol rearrangement of two substrates 2,3‐dimethyl‐2,3‐butanediol (7) and 2,3‐diphenyl‐2,3‐butanediol (12) was investigated. Acidic aqueous solvent was modeled by H~3~O^+^ and 12H~2~O. The reaction paths were promoted by a hydrogen‐bond circuit of H~3~O^+^(H~2~O)~2~ and were determined as completely concerted processes. Protonated species and carbocations as intermediates also do not intervene during the pinacol rearrangement. Active functions of proton relays along the hydrogen bonds in the two rearrangements were demonstrated. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2007