Title: Reaction Dynamics of the 4-Methylphenyl Radical ( p -Tolyl) with 1,2-Butadiene (1-Methylallene): Are Methyl Groups Purely Spectators?

Abstract

The reactions of the 4-tolyl radical (C₆H₄CH₃) and of the D7-4-tolyl radical (C₆D₄CD₃) with 1,2-butadiene (C₄H₆) have been probed in crossed molecular beams under single collision conditions at a collision energy of about 54 kJ mol^-1 and studied theoretically using ab initio G3(MP2,CC)//B3LYP/6-311G** and statistical RRKM calculations. The results show that the reaction proceeds via indirect scattering dynamics through the formation of a van-der-Waals complex followed by the addition of the radical center of the 4-tolyl radical to the C1 or C3 carbon atoms of 1,2-butadiene. The collision complexes then isomerize by migration of the tolyl group from the C1 (C3) to the C2 carbon atom of the 1,2-butadiene moiety. The resulting intermediate undergoes unimolecular decomposition via elimination of a hydrogen atom from the methyl group of the 1,2-butadiene moiety through a rather loose exit transition state leading to 2-para-tolyl-1,3-butadiene (p4), which likely presents the major reaction product. Our observation combined with theoretical calculations suggest that one methyl group (at the phenyl group) acts as a spectator in the reaction, whereas the other one (at the allene moiety) is actively engaged in the underlying chemical dynamics. On the contrary to the reaction of the phenyl radical with allene, which leadsmore » to the formation of indene, the substitution of a hydrogen atom by a methyl group in allene essentially eliminates the formation of bicyclic PAHs such as substituted indenes in the 4-tolyl plus 1,2-butadiene reaction.« less

Authors:

Kaiser, Ralf I. ^[1]; Dangi, Beni B. ^[1]; Yang, Tao ^[1]; Parker, Dorian S. N. ^[1]; Mebel, Alexander M. ^[2]

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+ Show Author Affiliations

1. Univ. of Hawaii at Manoa, Honolulu, HI (United States)
2. Florida International Univ., Miami, FL (United States)

Publication Date:

Fri Aug 01 00:00:00 EDT 2014

Research Org.:

Univ. of Hawaii at Manoa, Honolulu, HI (United States); Florida International Univ. (FIU), Miami, FL (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1602873

Grant/Contract Number:  

FG02-03ER15411; FG02-04ER15570

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment, and General Theory

Additional Journal Information:

Journal Volume: 118; Journal Issue: 32; Journal ID: ISSN 1089-5639

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; gas-phase chemistry; physical-organic chemistry; bimolecular reaction; reaction mechanism; combustion