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SIDDICK ICLI, UNDIL A. KANDIL, C. THANKACHAN, and THOMAS T. TIDWELL. Can. J. Chem. 53,979 (1975).The relative rates of decomposition of peroxyesters in cumene at 100" and their activation parameters AH* (kcal/mol) and ASf (cal deg-I mol-') were tert-butyl perbenzoate (1) 1.0, 34.0, 9.3; tert-butyl pertoluate (7) 1.3, 32.2, 4.8; tert-butyl permesitoate (8) 11, 31.9, 8.4; and tert-butyl2,4,6-tri-tert-butylperbenzoate (9) 29, 32.9, 13.0. Each peroxyester yielded the corresponding acid as one of the products. The reactions are all interpreted as proceeding through a rate-determining scission of the 0-0 bond to yield a benzoyloxy radical, which then undergoes competitive decarboxylation and hydrogen abstraction from the solvent. The small rate acceleration due to apara substituent is interpreted as due to a polar factor and the larger rate enhancing effect of the ortho substituents is interpreted as due to destabilization of the ground state due to twisting of the carboxyl group out of conjugation with the ring. perbenzoate de tert-butyle (9) 29, 32.9, 13.0. Chaque peroxyester conduit entre autre ii l'acide correspondant. On interprete toutes les reactions en fonction d'une Ctape dkterminante de la reaction qui impliquerait la scission du lien 0-0 conduisant au radical benzoyloxy qui subirait ensuite une decarboxylation ou enleverait un hydrogene du solvant. On attribue la petite augmentation de vitesse due ii un substituant en para a des facteurs polaires; par ailleurs l'augmentation importante observee lorsqu'il y a des substituants en position ortho implique une dtstabilisation de 1'6tat fondamental due ii une rotation du groupement carboxyle hors du plan de conjugaison du cycle.[Traduit par le journal]

Tri-isopropylmethyl is one of the most stable aliphatic hydrocarbon radicals known, and displays an e.s.r. spectrum indicative of an sp2 hybridization with the three p-hydrogens symmetrically aligned in the plane orthogonal to the p-orbital containing the unpaired electron.

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