DFT and ab-initio study on the mechanism of the gas-phase elimination kinetics of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene and their isomerization

Issue title: III Congress of Theoretical and Computational Physical Chemistry, 2–4 December 2010, Altos de Pipe, Caracas, Venezuela

Guest editors: Humberto Soscunxy, Fernando Ruettez and Anibal Sierraltaz

Article type: Research Article

Authors: Lezama, Jesús^{a; b} | Mora, José R.^a | Márquez, Edgar^b | Córdova, Tania^c | Chuchani, Gabriel^{a; *}

Affiliations: [a] Centro de Química, Instituto Venezolano de Investigaciones Científicas (I.V.I.C.), Caracas, Venezuela | [b] Escuela de Ciencias, Universidad de Oriente, Cumaná, Venezuela | [c] Department of Medicinal Chemistry, College of Pharmacy, University of Florida, Gainesville, FL, USA | [x] Centro Tecnológico, Instituto Venezolano de Investigaciones Científicas, IVIC, Caracas, Venezuela | [y] Departamento de Química, Facultad Experimental de Ciencias, La Universidad del Zulia LUZ, Maracaibo, Venezuela | [z] Centro de Química, Instituto Venezolano de Investigaciones Científicas, IVIC, Caracas, Venezuela

Correspondence: [*] Corresponding author: Gabriel Chuchani, Centro de Química, Instituto Venezolano de Investigaciones Científicas (I.V.I.C.), Apartado 21827, Caracas, Venezuela. E-mail: [email protected]

Abstract: The mechanisms of the gas-phase elimination kinetics of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene and their interconversion have been examined at MP2 and DFT levels of theory. These halide substrates yield isoprene and hydrogen chloride. The results MPW1PW91 calculations agree with the experimental kinetic parameters showing the elimination reaction occurs at greater rate for 1-chloro-3-methylbut-2-ene than that for the 3-chloro-3-methylbut-1-ene isomer. The mechanism for the molecular elimination of 1-chloro-3-methylbut-2-ene suggests proceeding through an uncommon six-membered cyclic transition state for alkyl halides in the gas phase, while 3-chloro-3-methylbut-1-ene eliminates through the usual four-membered cyclic transition state. The elongation and subsequent polarization of the C-Cl bond, in the direction of Cδ+…Clδ-, is rate determining step of these reactions. The isomerization of 1-chloro-3-methylbut-2-ene and 3-chloro-3-methylbut-1-ene was additionally studied. The 1-chloro-3-methylbut-2-ene converts to 3-chloro-3-methylbut-1-ene easier than the reverse reaction. This means that 1-chloro-3-methylbut-2-ene was found thermodynamically more stable than 3-chloro-3-methylbut-1-ene.

Keywords: 1-chloro-3-methylbut-2-ene, 3-chloro-3-methylbut-1-ene, ab initio and DFT theory, gas-phase elimination, kinetics, mechanism

DOI: 10.3233/JCM-2012-0412

Journal: Journal of Computational Methods in Sciences and Engineering, vol. 12, no. 4-6, pp. 247-260, 2012