Nucleophilic substitution in certain bicyclic sesquiterpene alcohols under chemical lonization conditions

Substitution of amino for hydroxyl groups in certain sesquiterpene alcohols has been studied by chemical ionization mass spectrometry using ammonia and ammouia-d₃ as the reagent gases, and by mass-analysed ion kinetic energy spectrometry and collision-induced decomposition mass-analysed ion kinetic energy measurements. Depending upon the source conditions and the nature of the substrates, both S_Ni and S_N1 mechanisms have been found to operate. No evidence is obtained for an S_N2 mechanism in these compounds. In centdarol and isocentdarol, addition of NH₃ to the double bond, followed by elimination of H₂O, also contributes to the substitution process. Attack of NH₄]⁺ on the epoxide function, followed by loss of H₂O, appears to lead to the substitution ions in epoxycentdarol, epoxyisocentdarol and epoxyhimachalol.