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NMR of Terminal Oxygen. Part 14 . Kinetically stabilized simple enols containing methylated uracil groups: Application of a 17 O‐NMR test of H‐bonding
Author(s) -
Zhuo JinCong,
Wyler Hugo,
Péchy Peter,
Dahn Hans
Publication year - 1994
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.19940770131
Subject(s) - chemistry , steric effects , enol , proton nmr , ring (chemistry) , nmr spectra database , crystallography , double bond , solvent , uracil , stereochemistry , nuclear magnetic resonance spectroscopy , spectral line , polymer chemistry , organic chemistry , catalysis , physics , astronomy , dna , biochemistry
Abstract In the crystalline N,N′ ‐dimethylated uracil derivatives 2a , b , the kinetically stabilized enol group forms an H‐bond with OC(4), as demonstrated by increased shielding of specifically labelled 2a and 2b in the 17 O‐NMR spectra (Δδ( 17 O)(C(4)—O) −30 ppm); absence of dilution and solvent effects show that the H‐bridge is intra‐molecular, forming an eight‐membered chelate ring. The (apparent) shielding effect Δδ( 17 O) in 2a, b is larger than that in salicylamide. The strong H‐bond explains why the enols 2 , in spite of the absence of steric hindrance, are kinetically stabilized.