Issue 47, 2017

Structure–reactivity correlations of the abnormal Beckmann reaction of dihydrolevoglucosenone oxime

Abstract

A structural, spectroscopic and computational study of a series of oximes was undertaken to investigate how geometric and structural changes relevant to the reaction coordinate for the Beckmann reaction (normal Beckmann) and Beckmann fragmentation (abnormal Beckmann) manifest in the ground state. X-ray structures of a range of oximes derived from dihydrolevoglucosan (Cyrene™; which undergoes the abnormal Beckmann reaction), in which the oxygen substituent was systematically varied were determined. As the electron demand of the OR group increased, the major structural changes included lengthening of the N–OR bond distance, and a decrease in the magnitude of the C2[double bond, length as m-dash]N–O bond angle, consistent with the changes seen for cyclohexanone oximes, which undergo the normal Beckmann reaction. However, unique to the Cyrene oximes, an increase in the length of the fissile C1–C2 bond was observed, which correlated with a decrease in the 13C–13C 1-bond coupling constants as the electron demand of the OR substituent increased. Computational studies of Cyrene and cyclohexanone oximes using Natural Bond Orbital analysis support an electronic structure involving n(O) → σ*C1–C2 and σC1–C2 → σ*N–O localized orbital interactions.

Graphical abstract: Structure–reactivity correlations of the abnormal Beckmann reaction of dihydrolevoglucosenone oxime

Supplementary files

Article information

Article type
Paper
Submitted
10 Oct 2017
Accepted
13 Nov 2017
First published
14 Nov 2017
This article is Open Access
Creative Commons BY license

Org. Biomol. Chem., 2017,15, 10105-10115

Structure–reactivity correlations of the abnormal Beckmann reaction of dihydrolevoglucosenone oxime

A. Alhifthi, B. L. Harris, L. Goerigk, J. M. White and S. J. Williams, Org. Biomol. Chem., 2017, 15, 10105 DOI: 10.1039/C7OB02499A

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements