Alkyl Substituent Effects on Dioxetane Properties. Tetraethyl-, Dicyclohexylidene-, and 3,4-Dimethyl-3,4-di-n-butyldioxetanes. A Discussion of Decomposition Mechanisms

Article abstract of DOI:10.1021/jo01314a007

A series of three closely related, symmetric, alkyl-substituted dioxetanes was synthesized: tetraethyldioxetane (1), cyclohexylidenedioxetane (2), and 3,4-dimethyl-3,4-di-n-butyldioxetane (a 1:1 mixture of cis and trans isomers; 3).Their unimolecular thermolysis gives, respectively, 3-pentanone, cyclohexanone, and 2-hexanone.The activation parameters are E_a = 30.8 kcal/mol and log A = 15.2 for 1, E_a = 27.7 kcal/mol and log A = 13.8 for 2, and E_a = 25.7 kcal/mol and log A = 12.8 for 3.In xylenes, the yields of excited triplet ketones from 1-3, determined fromthe intensity of chemiluminescence in the presence of 9, 10-dibromoanthracene or europium tris(thenoyltrifluoroacetonate)-1,10-phenanthroline, are 0.6, 0.3, and 0.3 (+/-50percent).The ratio of triplet to singlet excited ketones,determined with 9,10-diphenylanthracene or perylene, is ><*>100 in all cases.Thus 1 is more stable than either 2 or 3 (E_a of 1 is 5 kcal higher than that of 3), and it also gives more excited products.These results are discussed in term of current theories of stepwise thermolysis of dioxetanes.