Cooperative intramolecular hydrogen bonds in the structure of 5,5′-dibromo-3-diethylaminomethyl-2,2′-biphenol

Abstract

Crystals of 5,5′-dibromo-3-diethylaminomethyl-2,2′-biphenol were examined using X-ray diffraction and FT-IR spectroscopy. The space group is P2 1/ n with a=8.617(2), b=16.356(3), c=12.854(3) A ̊ , β=108.03(3)° and Z=4. The molecule exists in the crystal in zwitterionic state as a result of proton transfer from a hydroxyl group to the adjacent amino group. These two groups, together with the hydroxyl group of the second phenol moiety are involved in a system of cooperative intramolecular hydrogen bonds, O(2)H⋯O(1) −H +N(1). The O⋯O and O⋯N distances are 2.476(5) and 2.584(5) Å, the O–H and H–N distances 0.89 and 1.04 Å, and the O–H⋯O and O⋯H–N + angles 163 and 141°, respectively. The IR spectra of the crystals are consistent with the results of the X-ray analysis. Instead of a continuous absorption, only broad bands are found indicating very low proton polarizability in the two types of intramolecular hydrogen bonds.