Direct observation of aminyl radical intermediate during single-crystal to single-crystal photoinduced Orton rearrangement

Pance Naumov, Kenji Sakurai, Masahiko Tanaka, Hideyuki Hara

Research output: Contribution to journalArticle

Abstract

A photoinduced analogue of the thermal Orton rearrangement reaction by which an N-chlorine atom from a side amino group is transferred to a phenyl ring was studied in the solid state. Contrary to the mixture of products obtained in solution, in the N-chloro-N-acetylaminobenzene crystals the photoreaction proceeds with complete preservation of crystallinity, affording selectively and quantitatively the para isomer of chloroacetanilide. Study of the reaction mechanism by in situ steady-state photodiffraction, a combination of photoexcitation by UV light and single-crystal X-ray diffraction analysis, provided evidence for creation of N-acetyl-N-phenylaminyl (AcPhṄ) radical as a metastable reaction intermediate. The structure of the aminyl radical produced in 9.2% yield from the major disordered component in the statically 85.6:14.4 disordered crystal was directly observed for the first time. The unprecedented stability of the radical is prescribed to the solid-state cage effect, the reactive center of the radical species being locked away from the reactive target molecules. The creation of the radical and its head-to-tail chain reaction within the undulated hydrogen-bonded ribbons involving the acetyl carbonyl group are employed to explain the high selectivity of the photoinduced single-crystal to single-crystal Orton rearrangement. On the basis of the change of the crystal structure and the physicochemical data, a three-center five-atom mechanism involving homolytic cleavage of the N-Cl bond followed by hydrogen abstraction by the carbonyl group is suggested for the solid-state photoinduced Orton rearrangement.

Original languageEnglish (US)
Pages (from-to)10373-10378
Number of pages6
JournalJournal of Physical Chemistry B
Volume111
Issue number35
DOIs
StatePublished - Sep 6 2007

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Single crystals
Hydrogen
single crystals
Reaction intermediates
Atoms
Crystals
solid state
Photoexcitation
Chlorine
Ultraviolet radiation
Isomers
X ray diffraction analysis
Crystal structure
reaction intermediates
hydrogen
Molecules
photoexcitation
ribbons
crystals
chlorine

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

Cite this

Direct observation of aminyl radical intermediate during single-crystal to single-crystal photoinduced Orton rearrangement. / Naumov, Pance; Sakurai, Kenji; Tanaka, Masahiko; Hara, Hideyuki.

In: Journal of Physical Chemistry B, Vol. 111, No. 35, 06.09.2007, p. 10373-10378.

Research output: Contribution to journalArticle

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abstract = "A photoinduced analogue of the thermal Orton rearrangement reaction by which an N-chlorine atom from a side amino group is transferred to a phenyl ring was studied in the solid state. Contrary to the mixture of products obtained in solution, in the N-chloro-N-acetylaminobenzene crystals the photoreaction proceeds with complete preservation of crystallinity, affording selectively and quantitatively the para isomer of chloroacetanilide. Study of the reaction mechanism by in situ steady-state photodiffraction, a combination of photoexcitation by UV light and single-crystal X-ray diffraction analysis, provided evidence for creation of N-acetyl-N-phenylaminyl (AcPhṄ) radical as a metastable reaction intermediate. The structure of the aminyl radical produced in 9.2{\%} yield from the major disordered component in the statically 85.6:14.4 disordered crystal was directly observed for the first time. The unprecedented stability of the radical is prescribed to the solid-state cage effect, the reactive center of the radical species being locked away from the reactive target molecules. The creation of the radical and its head-to-tail chain reaction within the undulated hydrogen-bonded ribbons involving the acetyl carbonyl group are employed to explain the high selectivity of the photoinduced single-crystal to single-crystal Orton rearrangement. On the basis of the change of the crystal structure and the physicochemical data, a three-center five-atom mechanism involving homolytic cleavage of the N-Cl bond followed by hydrogen abstraction by the carbonyl group is suggested for the solid-state photoinduced Orton rearrangement.",
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