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n‐π‐Interaction in Enamines and Enaminoketones. A 15 N‐NMR. Study
Author(s) -
Schwotzer Willi,
Von Philipsborn Wolfgang
Publication year - 1977
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19770600507
Subject(s) - chemistry , enamine , chemical shift , amine gas treating , substituent , aniline , computational chemistry , kinetic isotope effect , enthalpy , medicinal chemistry , stereochemistry , organic chemistry , catalysis , thermodynamics , deuterium , quantum mechanics , physics
15 N‐Chemical shifts of 32 enamines, 11 enaminoketones and 28 closely related amines have been determined with the isotope in natural abundance. In order to eliminate substituent effects, differential chemical shifts Δδ(N) are defined as δ N (amine)‐δ N (enamine). This parameter is shown to correlate well with the free enthalpy of activation Δ G # for restricted rotation about the NC(α) bond in enamines with extended conjugation. Δδ(N) values of substituted anilinostyrenes correlate also with 13 C‐chemical shifts of the β‐carbon in the enamine system and with Hammett σ‐constants of the aniline substituents. The experimental results suggest that differential 15 N shifts are a useful probe to study n, π‐interaction in enamines.