Reactions of N-chlorobenzylalkylamines with sodium methoxide in methanol. Steric effects in elimination reactions

Bong-Rae Cho, Jun H. Maeng, Jong Chan Yoon, Tae Rin Kim

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Abstract

Reactions of N-chlorobenzylalkylamines in which the alkyl group is Me, Et, i-Pr, t-Bu, and sec-Bu with MeONa-MeOH have been investigated kinetically. The eliminations are quantitative and regiospecific, producing only benzylidenealkylamines. The reactions are first order in base and first order in substrate, and an E2 mechanism is evident. The relative rates of elimination at 25°C are 1/0.5/0.3/0.2/0.01 for Me/Et/i-Pr/sec-Bu/t-Bu alkyl substituents, respectively. The results are attributed to repulsive interaction between the alkyl group and the base in the transition state. Hammett ρ and kH/kD values decreased, but the ΔH and ΔS values increased with bulkier alkyl substituents. Changes in the transition-state parameters with the substrate steric effect are interpreted with variation in structure of the imine-forming transition states.

Original languageEnglish
Pages (from-to)4752-4756
Number of pages5
JournalJournal of Organic Chemistry
Volume52
Issue number21
Publication statusPublished - 1987 Dec 1

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Imines
Methanol
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  • Organic Chemistry

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Reactions of N-chlorobenzylalkylamines with sodium methoxide in methanol. Steric effects in elimination reactions. / Cho, Bong-Rae; Maeng, Jun H.; Yoon, Jong Chan; Kim, Tae Rin.

In: Journal of Organic Chemistry, Vol. 52, No. 21, 01.12.1987, p. 4752-4756.

Research output: Contribution to journalArticle

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AU - Cho, Bong-Rae

AU - Maeng, Jun H.

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AU - Kim, Tae Rin

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N2 - Reactions of N-chlorobenzylalkylamines in which the alkyl group is Me, Et, i-Pr, t-Bu, and sec-Bu with MeONa-MeOH have been investigated kinetically. The eliminations are quantitative and regiospecific, producing only benzylidenealkylamines. The reactions are first order in base and first order in substrate, and an E2 mechanism is evident. The relative rates of elimination at 25°C are 1/0.5/0.3/0.2/0.01 for Me/Et/i-Pr/sec-Bu/t-Bu alkyl substituents, respectively. The results are attributed to repulsive interaction between the alkyl group and the base in the transition state. Hammett ρ and kH/kD values decreased, but the ΔH‡ and ΔS‡ values increased with bulkier alkyl substituents. Changes in the transition-state parameters with the substrate steric effect are interpreted with variation in structure of the imine-forming transition states.

AB - Reactions of N-chlorobenzylalkylamines in which the alkyl group is Me, Et, i-Pr, t-Bu, and sec-Bu with MeONa-MeOH have been investigated kinetically. The eliminations are quantitative and regiospecific, producing only benzylidenealkylamines. The reactions are first order in base and first order in substrate, and an E2 mechanism is evident. The relative rates of elimination at 25°C are 1/0.5/0.3/0.2/0.01 for Me/Et/i-Pr/sec-Bu/t-Bu alkyl substituents, respectively. The results are attributed to repulsive interaction between the alkyl group and the base in the transition state. Hammett ρ and kH/kD values decreased, but the ΔH‡ and ΔS‡ values increased with bulkier alkyl substituents. Changes in the transition-state parameters with the substrate steric effect are interpreted with variation in structure of the imine-forming transition states.

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