Sur le mécanisme de la photodimérisation de la thymine

The study by the molecular orbital method of the electronic structure of the biological pyrimidine bases undergoing photodimerization leads to the conclusion that this reaction involves the triplet state of these molecules. It is shown that in this state the greatest concentration of the lone electrons is generally at C-5 on one of the half-filled orbitals and on C-6 on the other such orbital. When this is the situation, the rate of photodimerization parallels the total concentration of the uncoupled electrons on the C-5–C-6 bond.