6949-01-5Relevant academic research and scientific papers
Axially chiral pyridine compounds: Synthesis, chiral separations and determination of protonation dependent barriers to hindered rotation
Isikgor, Furkan Halis,Erol, Sule,Dogan, Ilknur
, p. 449 - 456 (2014/04/17)
Axially chiral enantiomeric 2-pyridylimino-3-pyridyl-thiazolidine-4-ones and -thiones have been synthesized and their rotational barriers around the N-3C(pyridyl) bond have been determined by variable temperature NMR or by thermal racemization of the micropreparatively resolved enantiomers. Rotational barriers of the unprotonated compounds ranged from 46 to 116 kJ/mol, depending on the substituent on the N-3-pyridyl ring and on the exocyclic oxygen or sulfur atoms of the thiazolidine ring. Protonation of the pyridine nitrogens by TFA caused a decrease in the barrier to the rotation by stabilizing the transition state of the rotations via hydrogen bonding interactions.
Molecular Conformation of N,N'-Diarylthioureas: an Assessment by 1H NMR and Infrared Spectroscopy
Sudha, L. V.,Manogaran, S.,Sathyanarayana, D. N.
, p. 591 - 596 (2007/10/02)
Several N,N'-dipyridyl- and N-phenyl-N'-pyridyl-thioureas were examined in different solvents at various temperatures by 1H NMR in order to study their conformational properties.The influence of concentration and the methyl substituent in the pyridine ring on the chemical shifts of the NH and pyridine groups was investigated.The observed chemical shifts are analysed in terms of the conformational properties of the molecules.Free energy barriers to the internal rotation about the C-N bonds have been determined.Infrared spectra have been measured to supplement the NMR studies.Intramolecular hydrogen bonding played a major role in the preferred conformation of pyridylthioureas.The data further revealed an interesting dynamic exchange phenomenon occuring in symmetric N,N'-dipyridylthioureas between two intramolecularly hydrogen bonded conformers.
