ISSN:
0749-1581
Keywords:
NMR
;
15N NMR
;
guanidines
;
heterocycles
;
hydrogen bonding
;
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Hydrogen bonding and electron distribution in some heterocyclic guanidines were studied by 15N NMR spectroscopy, using other substituted guanidines as points of reference. Solvent effects were used to distinguish the 15N NMR signals for their two sp2 nitrogen atoms, since ring nitrogen forms an intramolecular hydrogen bond and so is much less sensitive to solvent than is the guanidine unit. The effect of substituent is discussed in terms of competition between through-resonance and the more localized resonance of the π-inductive effect. These are favoured, respectively, by oxygen (nitro, acyl) and nitrogen (cyano) acceptor groups, whereas heterocycles, also nitrogen acceptors, occupy an intermediate position. Among the latter class, there are indications that the balance between these forms of resonance may be influenced by competitive conjugation with ring π-donor heteroatoms.
Additional Material:
2 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1260330510
