Mechanism of Thermal Z/E Isomerization of Substituted N-Benzylideneanilines. Nature of the Activated Complex with an sp-Hybridized Nitrogen Atom

Tsutomu Asano, Hiroyuki Furuta, Hans Jörg Hofmann, Renzo Cimiraglia, Yuho Tsuno, Mizue Fujio

Research output: Contribution to journalArticle

52 Citations (Scopus)

Abstract

In order to study the mechanism of thermal geometrical isomerization involving a sp2-hybridized nitrogen atom, kinetic effects of substituent, solvent, and pressure were studied in substituted N-benzylideneanilines. The effect of the substituent on the aniline moiety was almost independent of the electronic nature of the benzylidene group, and the results could be described satisfactorily by log (k/ko) = ρ[σ + r++ − σ) + r−σ)], except for the 4-(dimethylamino) group. The r− values were more than twice as large as r+, suggesting strongly that the aniline ring is in conjugation not with the carbon-nitrogen π bond but with the nitrogen lone pair in the transition state. The lower activation enthalpies and fairly large negative activation entropies observed in N-(4-X-benzylidene)-4-nitroanilines also support this view. When a dimethylamino group exists in the 4-position of the aniline ring, the rate constants observed were larger than that expected from the above equation. This deviation suggests the existence of a reaction route where the two phenyl groups become coplanar in the transition state. Ab initio calculations on selected N-phenylformaldimines and N-benzylideneanilines were performed to characterize the actual relation between both reaction possibilities as alternative and parallel routes, respectively. On the basis of the experimental data, the rate constants for the two inversion isomerizations were estimated by assuming parallel reactions for three cases.

Original languageEnglish
Pages (from-to)4418-4423
Number of pages6
JournalJournal of Organic Chemistry
Volume58
Issue number16
DOIs
Publication statusPublished - Jan 1 1993

Fingerprint

Isomerization
Nitrogen
Atoms
Rate constants
Chemical activation
Enthalpy
Entropy
Carbon
Kinetics
Hot Temperature
aniline

All Science Journal Classification (ASJC) codes

  • Organic Chemistry

Cite this

Mechanism of Thermal Z/E Isomerization of Substituted N-Benzylideneanilines. Nature of the Activated Complex with an sp-Hybridized Nitrogen Atom. / Asano, Tsutomu; Furuta, Hiroyuki; Hofmann, Hans Jörg; Cimiraglia, Renzo; Tsuno, Yuho; Fujio, Mizue.

In: Journal of Organic Chemistry, Vol. 58, No. 16, 01.01.1993, p. 4418-4423.

Research output: Contribution to journalArticle

Asano, Tsutomu ; Furuta, Hiroyuki ; Hofmann, Hans Jörg ; Cimiraglia, Renzo ; Tsuno, Yuho ; Fujio, Mizue. / Mechanism of Thermal Z/E Isomerization of Substituted N-Benzylideneanilines. Nature of the Activated Complex with an sp-Hybridized Nitrogen Atom. In: Journal of Organic Chemistry. 1993 ; Vol. 58, No. 16. pp. 4418-4423.
@article{49c2201b5f1240559c089d32d54be63c,
title = "Mechanism of Thermal Z/E Isomerization of Substituted N-Benzylideneanilines. Nature of the Activated Complex with an sp-Hybridized Nitrogen Atom",
abstract = "In order to study the mechanism of thermal geometrical isomerization involving a sp2-hybridized nitrogen atom, kinetic effects of substituent, solvent, and pressure were studied in substituted N-benzylideneanilines. The effect of the substituent on the aniline moiety was almost independent of the electronic nature of the benzylidene group, and the results could be described satisfactorily by log (k/ko) = ρ[σ∘ + r+(σ+ − σ∘) + r−(σ−−σ∘)], except for the 4-(dimethylamino) group. The r− values were more than twice as large as r+, suggesting strongly that the aniline ring is in conjugation not with the carbon-nitrogen π bond but with the nitrogen lone pair in the transition state. The lower activation enthalpies and fairly large negative activation entropies observed in N-(4-X-benzylidene)-4-nitroanilines also support this view. When a dimethylamino group exists in the 4-position of the aniline ring, the rate constants observed were larger than that expected from the above equation. This deviation suggests the existence of a reaction route where the two phenyl groups become coplanar in the transition state. Ab initio calculations on selected N-phenylformaldimines and N-benzylideneanilines were performed to characterize the actual relation between both reaction possibilities as alternative and parallel routes, respectively. On the basis of the experimental data, the rate constants for the two inversion isomerizations were estimated by assuming parallel reactions for three cases.",
author = "Tsutomu Asano and Hiroyuki Furuta and Hofmann, {Hans J{\"o}rg} and Renzo Cimiraglia and Yuho Tsuno and Mizue Fujio",
year = "1993",
month = "1",
day = "1",
doi = "10.1021/jo00068a042",
language = "English",
volume = "58",
pages = "4418--4423",
journal = "Journal of Organic Chemistry",
issn = "0022-3263",
publisher = "American Chemical Society",
number = "16",

}

TY - JOUR

T1 - Mechanism of Thermal Z/E Isomerization of Substituted N-Benzylideneanilines. Nature of the Activated Complex with an sp-Hybridized Nitrogen Atom

AU - Asano, Tsutomu

AU - Furuta, Hiroyuki

AU - Hofmann, Hans Jörg

AU - Cimiraglia, Renzo

AU - Tsuno, Yuho

AU - Fujio, Mizue

PY - 1993/1/1

Y1 - 1993/1/1

N2 - In order to study the mechanism of thermal geometrical isomerization involving a sp2-hybridized nitrogen atom, kinetic effects of substituent, solvent, and pressure were studied in substituted N-benzylideneanilines. The effect of the substituent on the aniline moiety was almost independent of the electronic nature of the benzylidene group, and the results could be described satisfactorily by log (k/ko) = ρ[σ∘ + r+(σ+ − σ∘) + r−(σ−−σ∘)], except for the 4-(dimethylamino) group. The r− values were more than twice as large as r+, suggesting strongly that the aniline ring is in conjugation not with the carbon-nitrogen π bond but with the nitrogen lone pair in the transition state. The lower activation enthalpies and fairly large negative activation entropies observed in N-(4-X-benzylidene)-4-nitroanilines also support this view. When a dimethylamino group exists in the 4-position of the aniline ring, the rate constants observed were larger than that expected from the above equation. This deviation suggests the existence of a reaction route where the two phenyl groups become coplanar in the transition state. Ab initio calculations on selected N-phenylformaldimines and N-benzylideneanilines were performed to characterize the actual relation between both reaction possibilities as alternative and parallel routes, respectively. On the basis of the experimental data, the rate constants for the two inversion isomerizations were estimated by assuming parallel reactions for three cases.

AB - In order to study the mechanism of thermal geometrical isomerization involving a sp2-hybridized nitrogen atom, kinetic effects of substituent, solvent, and pressure were studied in substituted N-benzylideneanilines. The effect of the substituent on the aniline moiety was almost independent of the electronic nature of the benzylidene group, and the results could be described satisfactorily by log (k/ko) = ρ[σ∘ + r+(σ+ − σ∘) + r−(σ−−σ∘)], except for the 4-(dimethylamino) group. The r− values were more than twice as large as r+, suggesting strongly that the aniline ring is in conjugation not with the carbon-nitrogen π bond but with the nitrogen lone pair in the transition state. The lower activation enthalpies and fairly large negative activation entropies observed in N-(4-X-benzylidene)-4-nitroanilines also support this view. When a dimethylamino group exists in the 4-position of the aniline ring, the rate constants observed were larger than that expected from the above equation. This deviation suggests the existence of a reaction route where the two phenyl groups become coplanar in the transition state. Ab initio calculations on selected N-phenylformaldimines and N-benzylideneanilines were performed to characterize the actual relation between both reaction possibilities as alternative and parallel routes, respectively. On the basis of the experimental data, the rate constants for the two inversion isomerizations were estimated by assuming parallel reactions for three cases.

UR - http://www.scopus.com/inward/record.url?scp=0000457634&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0000457634&partnerID=8YFLogxK

U2 - 10.1021/jo00068a042

DO - 10.1021/jo00068a042

M3 - Article

VL - 58

SP - 4418

EP - 4423

JO - Journal of Organic Chemistry

JF - Journal of Organic Chemistry

SN - 0022-3263

IS - 16

ER -