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Head‐to‐Tail Intermolecular Hydrogen Bonding of OH and NH Groups with Fluoride
Author(s) -
Ashokkumar Pichandi,
Ramakrishnan Vayalakkavoor T.,
Ramamurthy Perumal
Publication year - 2011
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201000463
Subject(s) - deprotonation , hydrogen bond , chemistry , intermolecular force , proton nmr , crystallography , photochemistry , molecule , stereochemistry , ion , organic chemistry
To explore the anion‐recognition ability of the phenolic hydroxyl group and the amino hydrogen, we synthesized three different acridinedione (ADD) based anion receptors, 1 , 2 and 3 , having OH, NH, and combination of OH and NH groups, respectively. Absorption, emission and 1 H NMR spectral studies revealed that receptor 1 , having only a phenolic OH group, shows selective deprotonation of the hydroxyl proton towards F − , which results in an “ON–OFF”‐type signal in the fluorescence spectral studies. Receptor 2 , which only has an amino hydrogen, also shows deprotonation of the amino hydrogen with F − , whereas receptor 3 (having both OH and NH groups) shows head‐to‐tail intermolecular hydrogen bonding of OH and NH groups with F − prior to deprotonation. The observation of hydrogen bonding of the OH and NH groups in a combined solution of 1 and 2 with F − in a head‐to‐tail hetero‐intermolecular fashion, and the absence of head‐to‐head and tail‐to‐tail intermolecular hydrogen bonding in 1 and 2 with F − , prove that the difference in the acidity of the OH and NH protons leads to the formation of an intermolecular hydrogen‐bonding complex with F − prior to deprotonation. The presence of this hydrogen‐bonding complex was confirmed by absorption spectroscopy, 3D emission contour studies, and 1 H NMR titration.