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Hydrogen‐Bond Accepting Strength of Five‐Membered N‐Heterocycles:The Case of Substituted Phenylpyrrolines and Myosmines
Author(s) -
Arnaud Virginie,
Berthelot Michel,
Felpin FrançoisXavier,
Lebreton Jacques,
Le Questel JeanYves,
Graton Jérôme
Publication year - 2009
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200900569
Subject(s) - chemistry , substituent , pyridine , molecule , nitrogen atom , ring (chemistry) , hydrogen bond , halogen , bond strength , halogen bond , acceptor , bifunctional , computational chemistry , hydrogen atom , nitrogen , stereochemistry , organic chemistry , group (periodic table) , alkyl , adhesive , physics , layer (electronics) , condensed matter physics , catalysis
The hydrogen‐bond (HB)accepting strengths of a series of five‐membered N‐heterocycles have been measured in CCl 4 solution and/or calculated by theoretical methods. These molecules present a great chemical versatility, ranging from very weak π bases up to strongly HB acceptors, imines and amines. Among these compounds, special attention has been paid to myosmines, which are bifunctional molecules containing two very similar pyridinic and pyrrolinic sp 2 nitrogen atoms. Infrared measurements provided the global HB basicities of these molecules, but the individual accepting strength of each nitrogen atom could not be achieved experimentally and had to be determined by theoretical calculations. Owing to their flexibility, the geometries of their different isomers were optimized and their basicities weighted by the calculated relative populations. To accurately estimate the individual HB strength of a nitrogen site, it was necessary to take into account a specific halogen bond between the second nitrogen atom and a solvent molecule. 1‐Pyrroline is a significantly stronger base than pyridine, but irrespective of the substituent on the pyridine ring, the pyrrolinic site is always the weakest HB acceptor in the myosmine molecules.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)