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MECHANISM OF THE PHOTOHYDRATION OF PYRIMIDINES: A FLASH PHOTOLYSIS STUDY *
Author(s) -
Garner A.,
Scholes G.
Publication year - 1985
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1985.tb03483.x
Subject(s) - pyrimidine , chemistry , flash photolysis , uracil , carbocation , photochemistry , ring (chemistry) , solvolysis , photodissociation , excited state , stereochemistry , kinetics , hydrolysis , organic chemistry , reaction rate constant , dna , biochemistry , physics , quantum mechanics , nuclear physics
— 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.