A study of the crystal and molecular structures of phenols with only intermolecular hydrogen bonding
The crystal structures and molecular geometrics of 41 phenols with only intermolecular hydrogen-bonding have been compared and analysed, with the following conclusions. (i) The electronic properties of substituents have effects on the phenolic hydroxy group which are measurable in terms of variations in the endocyclic angle at the phenolic hydroxy group. (ii) For mono-ortho-substituted phenols in the crystal the donor hydrogen bond lies on the opposite side of the C–O bond to the ortho substituent. (iii) The donor hydrogen bond is not required to be coplanar with the aromatic ring but may deviate by up to 40°. (iv) In di-ortho-substituted phenols there is a repulsive steric interaction between the donor hydrogen bond and one ortho substituent and this can be described in terms of both an in-plane and out-of-plane distortion of the hydrogen bonding. (v) The acceptor hydrogen bond shows large deviations from the phenolic ring plane and these deviations are greatly increased by ortho substitution. The crystal structures of the following compounds have been determined: 2-iodophenol, 2,6-di-isopropylphenol, 2,6-dibromo-4-methylphenol, 4-ethyl-2,6-di-iodophenol, 4-carboxy-2-iodophenol monohydrate, 4-carboxy-2,6-di-iodophenol, 4-carboxy-2,6-di-isopropylphenol, 2-methylsulphonylphenol monohydrate, 4-hydroxy-2-methylsulphonylphenol, 2-iodophenol–1,4-benzoquinone 2 : 1 molecular complex, 2-methylphenol–1,4-benzoquinone 2 : 1 molecular complex, 2,4,6-tri-iodophenol–tetramethylpyrazine 2 : 1 molecular complex, and 4′-hydroxy-4-methyl-2,3′,5′6,-tetraiododiphenyl ether.