Regiospecificity of intramolecular hydrogen transfer in cyclohexanol following chemical ionization

Both H₂O and HDO are eliminated from protonated d₁₁-cyclohexanol under chemical ionization conditions using methane as the reagent gas. The elimination of H₂O and HDO from the M+H]⁺ ions of cyclohexanol specifically labeled with deuterium in the 1; 2,6; 3,5; and 4 positions has been measured. It is found that there is considerable selectivity as to the position from which deuterium is lost in the elimination of HDO. That is, transfer from C-4 is favored, some transfer from C-3(5) occurs, little deuterium is lost from C-2(6) and none is lost from C-1. A mechanism involving ring protonation and ring opening followed by deuterium transfer to oxygen with subsequent loss of HDO is proposed to account for these observations.