Substituent effects in the gas‐phase eliminations of alpha;‐substituted alkyl chlorides the pyrolyses of 2‐chloro‐3‐methylbutane and pinacolyl chloride

Chuchani, Gabriel; Martín, Ignació; Alonso, Miguel E.

doi:10.1002/kin.550090512

Cited by 9 publications

(2 citation statements)

References 25 publications

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“…Calculations for CH 3 /F interchange in neopentyl fluoride gave a threshold energy of 87.2 kcal mol −1 , and the interchange reaction of methyl or other groups with a fluorine atom will have very high activation energies and interchange will not be important. Chuchani and co-workers have suggested that the small (10%) yield of 2,3-dimethyl-1-butene and 2,3-dimethyl-2-butene from pyrolysis of 2-chloro-3,3-dimethylbutane (pinacolyl chloride) arises from a Wagner−Meerwein rearrangement. However, a CH 3 /Cl interchange mechanism would be preferred by analogy to neopentyl chloride.…”

Section: Discussionmentioning

confidence: 99%

Isomerization of Neopentyl Chloride and Neopentyl Bromide by a 1,2-Interchange of a Halogen Atom and a Methyl Group

et al. 2010

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The recombination of chloromethyl and t-butyl radicals at room temperature was used to generate neopentyl chloride molecules with 89 kcal mol(-1) of internal energy. The observed unimolecular reactions, which give 2-methyl-2-butene and 2-methyl-1-butene plus HCl, as products, are explained by a mechanism that involves the interchange of a methyl group and the chlorine atom to yield 2-chloro-2-methylbutane, which subsequently eliminates hydrogen chloride by the usual four-centered mechanism to give the observed products. The interchange isomerization process is the rate-limiting step. Similar experiments were done with CD(2)Cl and C(CH(3))(3) radicals to measure the kinetic-isotope effect to help corroborate the proposed mechanism. Density functional theory was employed at the B3PW91/6-31G(d',p') level to verify the Cl/CH(3) interchange mechanism and to characterize the interchange transition state. These calculations, which provide vibrational frequencies and moments of inertia of the molecule and transition state, were used to evaluate the statistical unimolecular rate constants. Matching the calculated and experimental rate constants, gave 62 ± 2 kcal mol(-1) as the threshold energy for interchange of the Cl atom and a methyl group. The calculated models also were used to reinterpret the thermal unimolecular reactions of neopentyl chloride and neopentyl bromide. The previously assumed Wagner-Meerwein rearrangement mechanism for these reactions can be replaced by a mechanism that involves the interchange of the halogen atom and a methyl group followed by HCl or HBr elimination from 2-chloro-2-methylbutane and 2-bromo-2-methylbutane. Electronic structure calculations also were done to find threshold energies for several related molecules, including 2-chloro-3,3-dimethylbutane, 1-chloro-2-methyl-2-phenylpropane, and 1-chloro-2-methyl-2-vinylpropane, to demonstrate the generality of the interchange reaction involving a methyl, or other hydrocarbon groups, and a chlorine atom. The interchange of a halogen atom and a methyl group located on adjacent carbon atoms can be viewed as an extension of the halogen atom interchange mechanisms that is common in 1,2-dihaloalkanes.

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Section: Discussionmentioning

confidence: 99%

Isomerization of Neopentyl Chloride and Neopentyl Bromide by a 1,2-Interchange of a Halogen Atom and a Methyl Group

et al. 2010

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“…of decomposition of 2-chloro-2-methylbutane (1) and of 2-chloro-2,3-dimethylbutane (2) indicates that for long reaction times the final pressure Pf should be twice the initial pressure P0. The average experimental results of…”

Section: Resultsmentioning

confidence: 99%

Homogeneous unimolecular gas-phase elimination kinetics of 2-chloro-2-alkylpropanes. The electronic effect of alkyl substituents on the .alpha.-carbon of tertiary chlorides

Chuchani¹,

Martín²

1980

J. Phys. Chem.

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The pyrolysis kinetics of 2-chloro-2-methylbutane and 2-chloro-2,3-dimethylbutane have been investigated, in a static system and seasoned vessel, over the pressure range of 50-280 torr and the temperature range of 260-320 °C. The reactions are homogeneous and unimolecular, follow a first-order law, and are invariable to the presence of a cyclohexene inhibitor. The temperature dependence of the rate coefficients is given by the following Arrhenius equations: for 2-chloro-2-methylbutane, log kx (s_1) = (13.77 ± 0.25) -(184.1 ± 2.6) kJ-mol"1 (2.303RD-1; for 2-chloro-2,3-dimethylbutane, log kx (s'1) = (13.33 ± 0.18) -(175.3 ± 1.9) kJ-mol"1 (2.303RT)'1. The distribution of the olefin products from these reactions has been quantitatively determined and reported in details. The alkyl series ((CH3)3C, (CH3)2CH, CH3CH2, CH3, and H) in the tertiary halides, 2-chloro-2alkylpropanes, influence the rate of elimination by electronic effect. This is similar to those obtained with a-and /3-alkyl-substituted ethyl chlorides. The plot of log k/kQ vs. *( ) gives a very good straight line with p* = -4.75, r = 0.994, and intercept = 0.048 at 300 °C. The previous and present results reveal that, if a reaction center at the transition state of an organic molecule is markedly polar, the +7 inductive electron release of alkyl substituents may affect gas-phase elimination processes.

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Pyrolysis of Organic Halides

Chuchani

2009

Patai's Chemistry of Functional Groups

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Introduction Organic Fluoro Compounds Organic Chloro Compounds Organic Bromo Compounds Organic Iodo Compounds Competitive Dehydrohalogenation Five‐Membered Transition State Six‐Membered Transition State Neighboring Group Participation Rearrangements Acid Halides Chloroformates Acknowledgment

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Substituent effects in the gas‐phase eliminations of alpha;‐substituted alkyl chlorides the pyrolyses of 2‐chloro‐3‐methylbutane and pinacolyl chloride

Cited by 9 publications

References 25 publications

Isomerization of Neopentyl Chloride and Neopentyl Bromide by a 1,2-Interchange of a Halogen Atom and a Methyl Group

Isomerization of Neopentyl Chloride and Neopentyl Bromide by a 1,2-Interchange of a Halogen Atom and a Methyl Group

Homogeneous unimolecular gas-phase elimination kinetics of 2-chloro-2-alkylpropanes. The electronic effect of alkyl substituents on the .alpha.-carbon of tertiary chlorides

Pyrolysis of Organic Halides

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