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Restricted rotations about exocyclic partial double bonds. The electronic state of heteroaromatic six‐membered rings
Author(s) -
Kleinpeter E.,
Spitzner R.,
Schroth W.
Publication year - 1987
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.1260250807
Subject(s) - chemistry , cyanine , double bond , merocyanine , stereochemistry , crystallography , computational chemistry , photochemistry , polymer chemistry , photochromism , fluorescence , physics , quantum mechanics
Temperature‐dependent 13 C and 1 H NMR spectra of three series of six‐membered heteroaromatic systems with NR 2 substituents attached to pyrylium/thiopyrylium salts and pyrones/thiopyrones have been recorded. The rotational barriers thus determined about the exocyclic partial double bonds are discussed in terms of dominating mesomeric structures, in order to describe the electronic state and the spatial conditions in the molecular framework. Cyanine and merocyanine substructures have been identified by NMR and express the electronic state predominantly present in the compounds.