Botto, Robert E. and Schwartz, Joseph H. and Roberts, John D. (1980) Substituent effects on the nitrogen-15 and carbon-13 shieldings of some N-arylguanidinium chlorides. Proceedings of the National Academy of Sciences of the United States of America, 77 (1). pp. 23-25. ISSN 0027-8424. http://resolver.caltech.edu/CaltechAUTHORS:BOTpnas80
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The 13C and 15N chemical shifts of five N-arylguanidinium chlorides carrying polar substituents, ranging in character from 4-methoxy to 4-nitro groups, have been determined by NMR spectroscopy at the natural-abundance level of 13C and 15N in dimethyl sulfoxide solution. Comparison of the 13C shifts of these salts with those of monosubstituted benzenes shows that the guanidinium group induces an average downfield shift of -5.8 ppm of the resonance of the aryl carbon to which it is attached (C1), an average upfield shift of +4.2 ppm for C2 and C6, and a small upfield shift of +1.9 ppm for C4. The shifts of C3 and C5 are small and erratic relative to the corresponding carbons in monosubstituted benzenes. The 15N resonances of the guanidinium nitrogens are quite sensitive to electric effects resulting from substitution of polar groups at C4. The 15N shift of the ==NAr nitrogen relative to that of the salts suggests that the predominant tautomer for N-arylguanidines is (H2N)2C==NAr. The 15N shifts of the (NH2) 2 nitrogens correlate rather well with σp- parameters, whereas the shifts of the -NHAr nitrogens seem to correlate only with R values derived from the σp- substituent constants.
|Additional Information:||Copyright © 1980 by the National Academy of Sciences. Contributed by John D. Roberts, August 20, 1979. This is contribution no. 6099 from the Gates and Crellin Laboratories of Chemistry. These studies were supported by the National Science Foundation and by U.S. Public Health Service Grant GM-11072 from the Division of General Medical Sciences. The National Science Foundation also provided a Summer Undergraduate Research Fellowship (1977) for J.H.S.|
|Subject Keywords:||nuclear magnetic resonance spectroscopy; electrical effects; guanidine tautomers|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||01 Sep 2006|
|Last Modified:||26 Dec 2012 09:00|
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