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Solvent effect on the 13 C and 15 N NMR chemical shifts and rotational barriers in N , 1 N 1 ‐dimethyl‐and N , 1 N 1 ‐hexamethylene‐ N 2 ‐phenylformamidines
Author(s) -
Wawer Iwona
Publication year - 1989
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.1260271105
Subject(s) - chemistry , chemical shift , cyclohexane , hydrogen bond , solvent , protonation , solvent effects , nmr spectra database , carbon 13 nmr , proton nmr , acceptor , computational chemistry , molecule , crystallography , spectral line , organic chemistry , ion , physics , astronomy , condensed matter physics
Solvent‐induced 13 C NMR chemical shifts of N 1 , N 1 ‐dimethyl‐ N 2 ‐phenylformamidine can be correlated with the acceptor number of solvents, AN, and also with the π* and α parameters of Kamlet and Taft. No correlation was found for the height of the rotational barrier around the CN 1 bond. The self‐association of formamidine and the influence of polar, aprotic solvents cause an increase in Δ G 1 of approximately 1 kJ mol −1 whereas, contrary to expectations, the Δ G 1 values found in hydrogen‐bonding solvents are smaller than in cyclohexane. The barrier, however, increases with the strength of the hydrogen bond and on protonation. Downfield shifts of the N 1 and upfield shifts of the N 2 signals were observed in the 15 N NMR spectra of formamidine when the strength of the hydrogen bond with the solvent increased.