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Relationships between the acidity of the Z and E isomers of N ‐Nitroso‐ N ‐alkyl‐α‐amino acids and their conformations
Author(s) -
Liberek Bogdan,
Ciarkowski Jerzy,
Plucińska Krystyna,
Stachowiak Krystyna
Publication year - 1982
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270180306
Subject(s) - chemistry , intramolecular force , stereochemistry , alkyl , medicinal chemistry , alanine , glycine , hydrogen bond , nitroso , amino acid , molecule , organic chemistry , biochemistry
The acidity constants of both Z and E conformational isomers of five N ‐nitroso‐ N ‐alkyl‐α‐amino acids, ONN(R 1 )CH(R 2 )COOH, are determined by the observation of selected pH titrated 1 H NMR signals. For two glycine derivatives (1, R 1 CH 3 , R 2 H, ONSar; 2, R 1 C 2 H 5 , R 2 H, ONEtGly) and two alanine derivatives (3, R 1 CH 3 , R 2 CH 3 , ONMeAla; 4, R 1 C 2 H 5 , R 2 CH 3 , ONEtAla) the E isomers appear to be stronger acids than the Z while for the third alanine derivative (5, R 1 n ‐C 3 H 7 , R 2 CH 3 , ONPrAla) the opposite is observed. These results, also including anisotropy effects associated with the NNO group, are discussed in terms of conformations. A 7‐membered ring conformation with an NO…HOOC intramolecular hydrogen bond is proposed to be statistically important in the Z isomers of 1, 2, 3 and, to a lesser extent, 4.