A crossed molecular beam and ab initio study on the formation of 5- and 6-methyl-1, 4-dihydronaphthalene (C11H12) via the reaction of meta-tolyl (C7H7) with 1, 3-butadiene (C4H6). Issue 12 (25th February 2015)

• Record Type: Journal Article
• Authors: Muzangwa, Lloyd G.; Yang, Tao; Parker, Dorian S. N.; Kaiser, Ralf. I.; Mebel, Alexander M.; Jamal, Adeel; Ryazantsev, Mikhail; Morokuma, Keiji
• Is Part Of: Physical chemistry chemical physics. Volume 17:Issue 12(2015)
• Page Start: 7699
• Page End: 7706
• Publication Date: 2015-02-25
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c5cp00311c
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : The crossed molecular beam reactions of the meta -tolyl radical with 1, 3-butadiene and D6-1, 3-butadiene were conducted at collision energies of 48.5 kJ mol −1 and 51.7 kJ mol −1 . Abstract : The crossed molecular beam reactions of the meta -tolyl radical with 1, 3-butadiene and D6-1, 3-butadiene were conducted at collision energies of 48.5 kJ mol −1 and 51.7 kJ mol −1 . The reaction dynamics propose a complex-forming reaction mechanism via addition of the meta -tolyl radical with its radical center either to the C1 or C2 carbon atom of the 1, 3-butadiene reactant forming two distinct intermediates, which are connected via migration of the meta -tolyl group. Considering addition to C1 proceeds by formation of a van-der-Waals complex below the energy of the separated reactants, we propose that in cold molecular clouds holding temperatures as low as 10 K, the reaction of the meta -tolyl radical with 1, 3-butadiene is de-facto barrier less. At elevated temperatures such as in combustion processes, the reaction can also proceed via addition to C2 by overcoming the entrance barrier to addition (11 kJ mol −1 ). Eventually, the resonantly stabilized free radical intermediate C11 H13 undergoes isomerization to a cis form, followed by rearrangement through two distinct ring closures at the para - and ortho -position of tolyl radical to yield cyclic intermediates. These intermediates then emit a hydrogen atom forming 6- and 5-methyl-1, 4-dihydronaphthalene via tight exit transition states. The steady state branching ratio, 70.0% and 29.2%, at the collision energy of 51.7 kJ mol −1, of 6- and 5-methyl-1, 4-dihydronaphthalene, respectively, is determined mainly by the rates of reverse ring opening of cyclic intermediates. The formation of the thermodynamically less stable 1- meta -tolyl- trans -1, 3-butadiene was found to be a less important pathway (0.8%). The reaction of the meta -tolyl radical with 1, 3-butadiene leads without entrance barrier to two methyl substituted PAH derivatives holding 1, 4-dihydronapthalene cores: 5- and 6-methyl-1, 4-dihydronaphthalene thus providing a barrierless route to odd-numbered PAH derivatives under single collision conditions.