The influence of steric and polar effects on hydrogen bonding in 2-(N,N-diethylamino)-methyl-4-NO₂-phenols

Abstract

Two crystal structures consisting of 2-(N,N-diethylamino)-methyl-4-NO₂-phenol molecules were determined. In the triclinic crystals (with a=9.527(2) Å,b=11.268(3) Å,c=11.408(3) Å, α=87.80(3)^o. β=69.62(3)^o, γ=81.82(3)^o, Z=4, space groupPĪ) asymmetric cyclic dimers were found, formed by two nonequivalent O⁻…H−N⁺ hydrogen bonds of 2.614(3) and 2.660(3) Å lengths. In the complex of 2-(N,N-diethylamino)-methyl-4-NO₂-phenol with 4-NO₂-phenol (orthorhombic crystals witha=20.732(4) Å,b=16.618(2) Å,c=10.452(2) Å,Z=8, space groupPbca) an intermolecular O⁻…H−O (2.525(2) Å) hydrogen bond between 4-NO₂-phenol and zwitterionic 2-(N,N-diethylamino)-methyl-4-NO₂-phenol was found. In the latter molecule the intramolecular O⁻…H−N⁺ (2.760(2) Å) bridge is formed. The zwitterionic molecules form chains along the crystallographicb axis by NH⁺… O (3.105(2) Å) hydrogen bridges. The N−H⁺ groups participate in bifurcated hydrogen bonds. The influence of the steric strain caused by N-alkyl chains and polar interactions of the NO₂ group on the character of the hydrogen bond and the structure of cyclic dimers is discussed. The IR and UV spectra determined show the full agreement in description of the hydrogen bonding schemes, simultaneously demonstrating a drastic rearrangement of these schemes upon going to CCl₄ solutions.