EFFECTS OF METHYLATION ON THE THERMAL STABILITY AND CHEMILUMINESCENCE PROPERTIES OF 1,2-DIOXETANES.

Article abstract of DOI:10.1021/ja00288a022

The unknown monomethyl derivative 1f and the parent 1,2-dioxetane 1g have been prepared and fully characterized. The influence of the degree and pattern of methyl substitution of the complete set of 1,2-dioxetanes 1a-g on the activation parameters ( DELTA H** DOUB DAG , DELTA S** DOUB DAG , and DELTA G** DOUB DAG ) and on the excitation yields ( phi **T and phi **S) have been determined. It was found that (1) the thermal stability increases with the degree of methylation, (2) the pattern of methylation does not alter appreciably thermal stability, (3) triplet n, pi * states are preferentially energized, and (4) the triplet and singlet excitation yields increase with the degree of methylation. These experimental results are compared with thermochemical estimates and rationalized in terms of the diradical hypothesis and energy surface crossings.