Date of Graduation

1982

Document Type

Dissertation/Thesis

Abstract

The thermal unimolecular decomposition of ethylbenzene, iso-propylbenzene, t-butylbenzene, n-propylbenzene, isobutylbenzene, neopentylbenzene, 4-ethylstyrene, 1-phenyl-1-butene, 1-1 diphenyl-ethane, and 2-2 diphenylpropane was studied using the very-low-pressure pyrolysis (VLPP) technique. Each reactant decomposed by way of c-c bond fission producing an alkyl radical plus a benzyl or benzylic-type radical. RRKM calculations show that the observed rate constants when combined with thermochemical estimates are consistent with the following high-pressure rate expressions: log(k/s('-1)) = 15.3 - (72.7/(theta)) for ethylbenzene (1053 - 1234K), log(k/s('-1)) = 15.8 - (71.3/(theta)) for isopropylbenzene (971 - 1151K), log(k/s('-1)) = 15.9 - (69.1/(theta)) for t-butylbenzene (929 - 1157K), log(k/s('-1)) = 15.3 - (69.6/(theta)) for n-propylbenzene (989 - 1195K), log(k/s('-1)) = 15.6 - (67.8/(theta)) for isobutylbenzene (922 - 1087K), log(k/s('-1)) = 15.5 - (64.3/(theta)) for neopentylbenzene (918 - 1064K), log(k/s('-1)) = 15.3 - (71.3/(theta)) for 4-ethylstyrene (1096 - 1186K), log(k/s('-1)) = 15.3 - (67.3/(theta)) for 1-phenyl-1-butene (1030 - 1115K), log (k/s('-1)) = 15.5 - (67.4/(theta)) for 1-1 diphenylethane (1000 - 1066K), and log(k/s('-1)) = 15.7 - (65.8/(theta)) for 2-2 diphenylpropane (910 - 1054K) where (theta)/kcal mol('-1) = 2.303 RT. Resulting activation energies combined with heat capacity data led to the following bond dissociation energies at 298K: DH('0)(PhCH(CH(,3))--CH(,3)) = 73.8 kcal mol('-1), DH('0)(PhC(CH(,3))(,2)--CH(,3)) = 72.9 kcal mol('-1), DH('0)(PhCH(,2)--C(CH(,3))(,3)) = 69.8 kcal mol('-1), DH('0)(H(,2)CCHPhCH(,2)--CH(,3)) = 72.5 kcal mol('-1), DH('0)(PhCHCHCH(,2)--CH(,3)) = 69.2 kcal mol('-1), DH('0)(Ph)(,2)CH--CH(,3)) = 69.8 kcal mol('-1), and DH('0)((Ph)(,2)CH(CH(,3))--CH(,3)) = 69.4 kcal mol('-1). Activation energies were also used to derive the following heats of formation at 298K: (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) In the cases of 4-ethylstyrene, 1-phenyl-1-butene, 1-1 diphenylethane, and 2-2 diphenylpropane relative activation energies for bond fission were related to relative resonance stabilization energies (RSE) in the resulting benzylic radical products. Relative to a RSE of 11 kcal mol('-1) for the benzyl radical PhCH(,2)(.) (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) experimental results were consistent with the following RSE at 298K: RSE(H(,2)CCHPhCH(,2)(.)) = 13.4 kcal mol('-1), RSE(PhCHCHCH(,2)(.)) = 16.7 kcal mol('-1), RSE((Ph)(,2)CH) = 15.0 kcal mol('-1), and RSE((Ph)(,2)CHCH(,3)) = 14.5 kcal mol('-1). These results were found to be in agreement with the predictions of an empirical technique for estimating RSE in benzylic radicals. Where appropriate, kinetic results were compared with previously reported results of "carrier" and shock tube experiments.

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