Characterization of the triplet state of aromatic esters and nitriles. Evaluation of the steric effect on the triplet of methyl mesitoate

Abstract

. Can. J. Chem. 55,2728Chem. 55, (1977. The phosphorescence emission and electron spin resonance spectra of methyl mesitoate (1) and mesitonitrile (2) have been studied in order to assess the stericeffect (inhibition of resonance) in the former. The triplet energy of 1 (80.5 kcal mol-') is considerably higher than that of 2 (74.2 kcal mol-') while the zero-field splitting parameters are very similar (1, Dlhc = 0.127 cm-', Elhc = 0.013 cm-' ; 2, Dlhc = 0.127 cm-l, Elhc = 0.006 cm-'). The triplet energy and zero-field splitting parameters of o-, m-, and p-methyl toluate and o-, m-, and p-tolunitrile are also reported.

Benzoates as photosensitization catalysts and auxiliaries in efficient, practical, light-powered direct C(sp3)–H fluorinations

“…Time-dependent Density Functional Theory (TD-DFT) calculations were used to calculate T 1 for MFB (78.3 kcal mol −1 , see ESI † ). Although the T 1 values for all these compounds 18,19 lay above that reported for SF (61.4 kcal mol −1 ), 9 a no correlation existed between the T 1 values and the efficiencies of the photochemical fluorinations of 1a–1d, confirming other factors underpinned successful reactivity. To probe further, we examined substrate 5b for which the catalytic method was ineffective, giving product 21 in only 8% yield ( Table 5 , entry 1).…”

Chemoselective Photorearrangements of Diazinobarrelenes. Deuterium Labeling Study

“…This kind of radical stabilization cannot be observed during the initial V−V bridging (Scheme , vide supra) because the radicals are not conjugated to the sp 2 atoms of the aryl moiety. The strong directional effects of the nitrile groups, which can stabilize diradicaloid intermediates, have enhanced the localization of the triplet energy on this part of the molecule 8 Resonance Structures of Barrelene 4 Generated through Initial A−V Bridging …”

Electronic excited states of small ring compounds. VII. Bicyclo[2.1.0]pentanes by the photocycloaddition of 1,2,3-triphenylcyclopropene to fumaro- and maleonitrile

“…This reasoning was based on the fact that both carbomethoxy and cyano substitution lowers the triplet energy of benzene by the same extent; methyl benzoate and cyanobenzene have essentially the same triplet energies (24). Baird (25) has proposed an empirical approach for estimating the energy of the 'twisted' TC,X* triplet of conjugated alkenes6 To use this approach to compare the relative triplet energies of two alkenes, one considers the relative stabilities of the pairs of radicals resulting from twisting each of the 7c bonds by 90".…”