| Abstract: | ![]()
Abstract— Based on comparisons between the microsecond flash photolysis of uracil and substituted uracils and the radiation chemistry of the corresponding 5,6-dihydro-2,4-dioxopyrimidines, it is proposed that the mechanism of photohydration of pyrimidine bases involves the formation of a pyrimidine carbocation. The effects of substitution in the pyrimidine ring and of pH are consistent with a proton transfer from water to the excited singlet state at theC–5 position of the pyrimidine ring. The resultant carbocation is thought to undergo solvolysis to form the photohydrate or eliminate a proton at N-l producing an intermediate isomeric form of the pyrimidine (isopyrimidine) which re-arranges to the parent pyrimidine by a first-order process. |
