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Influence of Electrostatic Interactions on Complexes with Short O···O Hydrogen Bonds in Basic Salts of Pyridine Betaines and Acid Salts of ω‐Phenyloalkanocarboxylic Acids
Author(s) -
Szafran Mirosław,
Kowalczyk Iwona,
Barczyński Piotr
Publication year - 1999
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.199900032
Subject(s) - chemistry , delocalized electron , pyridine , hydrogen bond , crystallography , methylene , isostructural , proton affinity , ring (chemistry) , proton , counterion , absorption (acoustics) , absorption spectroscopy , ion , stereochemistry , molecule , medicinal chemistry , protonation , crystal structure , organic chemistry , physics , quantum mechanics , acoustics
Abstract The isostructural complexes [C 5 H 5 N + (CH 2 ) n COO] 2 HX and [C 6 H 5 (CH 2 ) n COO] 2 HK (n = 1–4), which differ in their counterions and charge on the ring, were synthesized, and their powder FT‐IR spectra analyzed. All complexes containing a charged pyridine ring are of Hadži type iii, characterized by an intense broad (continuum) absorption below 1600 cm −1 typical of a short‐strong hydrogen bond (SSHB) with a delocalized proton and a single v C=O band. The positively charged nitrogen atoms interact electrostatically with the X − ion and, additionally, with one of the oxygen atoms of the carboxylic group, producing a more or less symmetric environment of the H‐bonded proton, and stabilizing the SSHB. The broad absorption of [C 6 H 5 CH 2 COO] 2 HK is very similar to that of other pyridine complexes. Upon addition of methylene groups the broad absorption moves to higher wavenumbers, the O···O distance is elongated, and the H‐bonded proton becomes more localized. In the spectrum of [C 6 H 5 (CH 2 ) 4 COO] 2 HK the v C=O and v as COO bands were found at 1704 and 1641 cm −1 , respectively, which shows that the H‐bonded proton is asymmetrically located. The observed variation of absorption with the number of CH 2 groups reflects changes of contacts between the K + ion and COO − groups.