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Physical Organic Chemistry of N-Substituted N'-Cyanoguanidenes.

Wan, Nan Chi. (1995) Physical Organic Chemistry of N-Substituted N'-Cyanoguanidenes. Doctoral thesis, University of Surrey (United Kingdom)..

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Abstract

A series of N-aryl-N'-cyanoguanidines and several related compounds have been prepared. 1H and 15N NMR spectroscopy of these, together with some 15N enriched analogues, show that the amino tautomer is preferred in DMSO solution. Lack of variation in δH for the nitrogen-bonded protons upon addition of water and increasing concentration indicates that prototropic tautomerisation is negligible on the NMR timescale. The variation of δH with temperature shows ‘amide-like’ hydrogen bonding to DMSO. 13C and 15N NMR signals have been assigned and variations in δC and δN have been interpreted in terms of a delocalised cyanoguanidine π system with a planar skeleton and minimal involvement of the aryl ring in the π delocalisation. Examination of X-ray crystal structures for N-cyano-N'-(4-methoxyphenyl)guanidine and N-cyano-N'-(4-methoxyphenyl)-N’-methylguanidine shows a planar cyanoguanidine with a tilted aryl ring, E geometry about the C=N bond and a cis arrangement of the Ar and NH2 groups about the ArN-C partial double bond. The N-(4-chlorophenyl)-N’-cyano-N,N,N-trimethylguanidine compound shows the ArNMe group twisted relative to the NMe2-C=N-CN portion resulting in reduced cyanoguanidine π delocalisation and giving rise to chirality in the crystal state. The pKa values in aqueous solution for proton loss from N-aryl-N'-cyanoguanidines were determined spectrophotometrically and lie in the range 10.9-12.7; the site of deprotonation is at ArNH. Treatment with Mel following deprotonation with n-butyl lithium yielded mono-, di- and trimethyl derivatives which have been isolated and characterised by NMR, microanalysis and mass spectroscopy; a breakdown product has also been isolated. Mechanisms for the breakdown and methylation pathways are proposed.

Item Type: Thesis (Doctoral)
Divisions : Theses
Authors : Wan, Nan Chi.
Date : 1995
Additional Information : Thesis (Ph.D.)--University of Surrey (United Kingdom), 1995.
Depositing User : EPrints Services
Date Deposited : 14 May 2020 14:56
Last Modified : 14 May 2020 15:05
URI: http://epubs.surrey.ac.uk/id/eprint/856765

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