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Crossed molecular beam studies of the reactions of allyl radicals, C3H5(X2A2), with methylacetylene (CH3CCH(X1A1)), allene (H2CCCH2(X1A1)), and their isotopomers.
J Phys Chem A. 2007 Jun 14; 111(23):4914-21.JP

Abstract

The chemical dynamics of the reaction of allyl radicals, C(3)H(5)(X(2)A(2)), with two C(3)H(4) isomers, methylacetylene (CH(3)CCH(X(1)A(1))) and allene (H(2)CCCH(2)(X(1)A(1))) together with their (partially) deuterated counterparts, were unraveled under single-collision conditions at collision energies of about 125 kJ mol(-1) utilizing a crossed molecular beam setup. The experiments indicate that the reactions are indirect via complex formation and proceed via an addition of the allyl radical with its terminal carbon atom to the terminal carbon atom of the allene and of methylacetylene (alpha-carbon atom) to form the intermediates H(2)CCHCH(2)CH(2)CCH(2) and H(2)CCHCH(2)CHCCH(3), respectively. The lifetimes of these intermediates are similar to their rotational periods but too short for a complete energy randomization to occur. Experiments with D4-allene and D4-methylacetylene verify explicitly that the allyl group stays intact: no hydrogen emission was observed but only the release of deuterium atoms from the perdeuterated reactants. Further isotopic substitution experiments with D3-methylacetylene combined with the nonstatistical nature of the reaction suggest that the intermediates decompose via hydrogen atom elimination to 1,3,5-hexatriene, H(2)CCHCH(2)CHCCH(2), and 1-hexen-4-yne, H(2)CCHCH(2)CCCH(3), respectively, via tight exit transition states located about 10-15 kJ mol(-1) above the separated products. The overall reactions were found to be endoergic by 98 +/- 4 kJ mol(-1) and have characteristic threshold energies to reaction between 105 and 110 kJ mol(-1). Implications of these findings to combustion and interstellar chemistry are discussed.

Authors+Show Affiliations

Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA.No affiliation info availableNo affiliation info availableNo affiliation info availableNo affiliation info available

Pub Type(s)

Journal Article

Language

eng

PubMed ID

17516638

Citation

Guo, Y, et al. "Crossed Molecular Beam Studies of the Reactions of Allyl Radicals, C3H5(X2A2), With Methylacetylene (CH3CCH(X1A1)), Allene (H2CCCH2(X1A1)), and Their Isotopomers." The Journal of Physical Chemistry. A, vol. 111, no. 23, 2007, pp. 4914-21.
Guo Y, Mebel AM, Zhang F, et al. Crossed molecular beam studies of the reactions of allyl radicals, C3H5(X2A2), with methylacetylene (CH3CCH(X1A1)), allene (H2CCCH2(X1A1)), and their isotopomers. J Phys Chem A. 2007;111(23):4914-21.
Guo, Y., Mebel, A. M., Zhang, F., Gu, X., & Kaiser, R. I. (2007). Crossed molecular beam studies of the reactions of allyl radicals, C3H5(X2A2), with methylacetylene (CH3CCH(X1A1)), allene (H2CCCH2(X1A1)), and their isotopomers. The Journal of Physical Chemistry. A, 111(23), 4914-21.
Guo Y, et al. Crossed Molecular Beam Studies of the Reactions of Allyl Radicals, C3H5(X2A2), With Methylacetylene (CH3CCH(X1A1)), Allene (H2CCCH2(X1A1)), and Their Isotopomers. J Phys Chem A. 2007 Jun 14;111(23):4914-21. PubMed PMID: 17516638.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Crossed molecular beam studies of the reactions of allyl radicals, C3H5(X2A2), with methylacetylene (CH3CCH(X1A1)), allene (H2CCCH2(X1A1)), and their isotopomers. AU - Guo,Y, AU - Mebel,A M, AU - Zhang,F, AU - Gu,X, AU - Kaiser,R I, Y1 - 2007/05/22/ PY - 2007/5/23/pubmed PY - 2007/5/23/medline PY - 2007/5/23/entrez SP - 4914 EP - 21 JF - The journal of physical chemistry. A JO - J Phys Chem A VL - 111 IS - 23 N2 - The chemical dynamics of the reaction of allyl radicals, C(3)H(5)(X(2)A(2)), with two C(3)H(4) isomers, methylacetylene (CH(3)CCH(X(1)A(1))) and allene (H(2)CCCH(2)(X(1)A(1))) together with their (partially) deuterated counterparts, were unraveled under single-collision conditions at collision energies of about 125 kJ mol(-1) utilizing a crossed molecular beam setup. The experiments indicate that the reactions are indirect via complex formation and proceed via an addition of the allyl radical with its terminal carbon atom to the terminal carbon atom of the allene and of methylacetylene (alpha-carbon atom) to form the intermediates H(2)CCHCH(2)CH(2)CCH(2) and H(2)CCHCH(2)CHCCH(3), respectively. The lifetimes of these intermediates are similar to their rotational periods but too short for a complete energy randomization to occur. Experiments with D4-allene and D4-methylacetylene verify explicitly that the allyl group stays intact: no hydrogen emission was observed but only the release of deuterium atoms from the perdeuterated reactants. Further isotopic substitution experiments with D3-methylacetylene combined with the nonstatistical nature of the reaction suggest that the intermediates decompose via hydrogen atom elimination to 1,3,5-hexatriene, H(2)CCHCH(2)CHCCH(2), and 1-hexen-4-yne, H(2)CCHCH(2)CCCH(3), respectively, via tight exit transition states located about 10-15 kJ mol(-1) above the separated products. The overall reactions were found to be endoergic by 98 +/- 4 kJ mol(-1) and have characteristic threshold energies to reaction between 105 and 110 kJ mol(-1). Implications of these findings to combustion and interstellar chemistry are discussed. SN - 1089-5639 UR - https://www.unboundmedicine.com/medline/citation/17516638/Crossed_molecular_beam_studies_of_the_reactions_of_allyl_radicals_C3H5_X2A2__with_methylacetylene__CH3CCH_X1A1___allene__H2CCCH2_X1A1___and_their_isotopomers_ L2 - https://dx.doi.org/10.1021/jp0714466 DB - PRIME DP - Unbound Medicine ER -
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