Elimination Reactions of (E)- and (Z)-Benzaldehyde O-Pivaloyloximes. Transition-State Differences for the Syn and Anti Eliminations Forming Nitriles

Bong-Rae Cho, Nam Soon Cho, Sang Kook Lee

Research output: Contribution to journalArticle

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Abstract

Elimination reactions of (E)- and (Z)-benzaldehyde O-pivaloyloximes 1 and 2 with DBU in MeCN have been investigated kinetically. The reactions are second order and exhibit substantial values of Hammett ρ and kH/kD values, and an E2 mechanism is evident. The rate of elimination from 2 is approximately 20 000-fold faster than that from 1. For reactions of 1 with DBU in MeCN, a Hammett ρ value of 2.4 ± 0.1, kH/kD = 2.7 ± 0.3, ΔH‡ = 12.5 ± 0.2 kcal/mol, and ΔS‡ = -31.0 ± 0.6 eu have been determined. The corresponding values for 2 are ρ = 1.4 ± 0.1, kH/kD = 7.8 ± 0.3, ΔH‡ = 8.8 ± 0.1 kcal/mol, and ΔS‡ = -23.6 ± 0.4 eu, respectively. The results indicate that the nitrile-forming anti eliminations from 2 proceed via a more symmetrical transition state with a smaller degree of proton transfer, less negative charge development at the β-carbon, and greater extent of triple-bond formation than that for the syn elimination.

Original languageEnglish
Pages (from-to)2230-2233
Number of pages4
JournalJournal of Organic Chemistry
Volume62
Issue number7
Publication statusPublished - 1997 Dec 1

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Nitriles
Proton transfer
Protons
Carbon
benzaldehyde

ASJC Scopus subject areas

  • Organic Chemistry

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Elimination Reactions of (E)- and (Z)-Benzaldehyde O-Pivaloyloximes. Transition-State Differences for the Syn and Anti Eliminations Forming Nitriles. / Cho, Bong-Rae; Cho, Nam Soon; Lee, Sang Kook.

In: Journal of Organic Chemistry, Vol. 62, No. 7, 01.12.1997, p. 2230-2233.

Research output: Contribution to journalArticle

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abstract = "Elimination reactions of (E)- and (Z)-benzaldehyde O-pivaloyloximes 1 and 2 with DBU in MeCN have been investigated kinetically. The reactions are second order and exhibit substantial values of Hammett ρ and kH/kD values, and an E2 mechanism is evident. The rate of elimination from 2 is approximately 20 000-fold faster than that from 1. For reactions of 1 with DBU in MeCN, a Hammett ρ value of 2.4 ± 0.1, kH/kD = 2.7 ± 0.3, ΔH‡ = 12.5 ± 0.2 kcal/mol, and ΔS‡ = -31.0 ± 0.6 eu have been determined. The corresponding values for 2 are ρ = 1.4 ± 0.1, kH/kD = 7.8 ± 0.3, ΔH‡ = 8.8 ± 0.1 kcal/mol, and ΔS‡ = -23.6 ± 0.4 eu, respectively. The results indicate that the nitrile-forming anti eliminations from 2 proceed via a more symmetrical transition state with a smaller degree of proton transfer, less negative charge development at the β-carbon, and greater extent of triple-bond formation than that for the syn elimination.",
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