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Low‐temperature (120 K) structure and vibrational spectrum of protonated proton sponge: the adduct of 1,8‐bis(dimethylamino)naphthalene (DMAN) with 4,5‐ dicyanoimidazole (DCI)
Author(s) -
Grech Eugeniusz,
Malarski Zbigniew,
SawkaDobrowolska Wanda,
Sobczyk Lucjan
Publication year - 1999
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/(sici)1099-1395(199904)12:4<313::aid-poc110>3.0.co;2-8
Subject(s) - chemistry , adduct , proton , excited state , raman spectroscopy , hydrogen bond , protonation , hydrogen atom , crystallography , intramolecular force , molecule , stereochemistry , atomic physics , organic chemistry , ion , physics , alkyl , quantum mechanics , optics
Low‐temperature (120 K) studies of the structure of the DMAN·DCI adduct indicate that in symmetrical [NHN] + hydrogen bridge of 2.571 (1) Å length (2.579(2) Å at room temperature) there is a disorder of the H‐atom occupying two positions at nitrogen atoms with a distance of 0.94(3) Å. The comparison with the situation at room temperature seems to show a very low barrier for the proton transfer. The low‐frequency vibrations with the participation of the whole N(CH 3 ) 2 groups observed in Raman and inelastic incoherent neutron scattering (IINS) spectra of about 100 cm −1 excited at room temperature cause the fundamental level of the protonic mode to penetrate or exceed the barrier. The bending CNC vibrations of about 500 cm −1 are strongly coupled with the protonic mode leading to Evans holes in the band ascribed to the 0 + → 0 − transition. This hypothesis is consistent with the literature data relating to theoretical studies on H 3 NHNH 3 + , which show that the barrier for the proton transfer disappears at the hydrogen bond length of about 2.55 Å. Copyright © 1999 John Wiley & Sons, Ltd.