Computational evidence for back donation in an N � O group based on modes of transmission of substituent effects in 3-(4�-substituted) phenylfuroxans

Balasubrahmanyam, SN and Ganguly, B and Lo, R and Rajan, MMB and Sreerag, MN and Sharafudeen, PC and Oshiya, RA and Rajendran, N (2021) Computational evidence for back donation in an N � O group based on modes of transmission of substituent effects in 3-(4�-substituted) phenylfuroxans. In: Journal of Chemical Sciences, 133 (1).

	PDF jou_che_sci_133-01_2021.pdf - Published Version Restricted to Registered users only Download (633kB) | Request a copy
	PDF 12039_2021_1885_MOESM1_ESM.pdf - Published Supplemental Material Restricted to Registered users only Download (425kB) | Request a copy

Abstract

The N-oxide nitrogen in C-4� substituted 3-phenyl furoxans occupies a position analogous to C-β in 4-substituted styrenes that have been examined for modes of transmission of substituent effects from the C-4 substituent to C-β. From geometry optimizations through high-level MO theory calculations, it was first ensured that the N-2�C-3 liaison in 3-(4�-substituted)phenyl furoxans retains as much double-bond character as it does in the case of furoxan bearing no substituents and that the para-substituted phenyl and furoxan rings maintain near uniplanarity. The calculations, carried out for such furoxans, chosen to represent a spectrum of effects from electron-donor to electron-acceptor, showed how the change in the 4�-substituent affects electron redistribution within N-oxide group in the way expected: while the residual positive charge at N increases the residual negative charge at O decreases. An increase in the N-oxide bond order (as measured by the Wiberg bond index), together with a small reduction in the N-2�O-6 bond length, was also found. That these effects were not artefacts of the calculation procedure was ensured when the calculations, repeated using a different functional, showed not only inverse dependence of positive N-2 and negative O-6 net charges on N-2�O-6 bond lengths but also confirmatory evidence from N-oxide bond dissociation and second-order perturbation energies. These results are interpreted as demonstrating graded back donation from O to N within the N � O group caused by a combined action of mesomerism and �-polarisation involving the substituent at the para-position of the phenyl group offering a spectrum of effects from electron-releasing to electron-withdrawing. Graphical abstract: Calculations at the B3LYP/6-31++G** level have shown that back donation from O to N in N � O in 3-(4�-X-phenyl) furoxans increase with a change of X from electron-donor to electron-acceptor.Figure not available: see fulltext. © 2021, Indian Academy of Sciences.

Item Type:	Journal Article
Publication:	Journal of Chemical Sciences
Publisher:	Springer
Additional Information:	The copyright for this article belongs to Springer
Keywords:	Bond length; Computation theory; Styrene; Transmissions, Calculation procedure; Double bond character; Electron acceptor; Electronwithdrawing; Geometry optimization; Inverse dependence; Second order perturbation; Substituent effect, Electrons
Department/Centre:	Division of Chemical Sciences > Organic Chemistry
Date Deposited:	30 Mar 2021 12:02
Last Modified:	30 Mar 2021 12:02
URI:	http://eprints.iisc.ac.in/id/eprint/68568

Actions (login required)

View Item