The Study of Hydrogen Bonding and Related Phenomena by Ultraviolet Light Absorption: Part Iv. Intermolecular Hydrogen Bonding in Anilines and Phenols

Abstract

Intermolecular hydrogen bonding in anilirles and phenols can be subdivided into bonding itlvolving solute molecules only, and into bonding involving both solute and solvent ~nolecules. Interactions which do not involve hydrogen bonding are also possible between solute and solvent moleci~les. Spectral elFects which may be associated with each of these interactions are described and discussed for anilines and phenols. By noting the effects of substituents on the various interactions, tentative conclusions can be deduced concerning the nature of these interactions. INTRODUCTIONIntermolecular hydrogen bonding is a well-lcnown pl~enomenon in a number of phenols and anilines, since the changes caused by the bonding can be detected by the changes in a number of physical properties such as melting points, solubilities, dipole moments, spectral effects, and other properties. The spectral changes caused by intermolecular hydrogen bonding in substituted benzoic acids have been discussed in previous parts of this series ( I ) . The purpose of the present paper is to extend this investigation to anilines and phenols. HYDROGEN BONDING BETWEEN SOLUTE MOLECULES ONLYVon I<eussler (2) has sholvn that an increase of the solute coi;centration beyond the inore readily accessible concentration range (i.e. solute concentration greater than ca.moles/liter) causes a concentration dependence in the C-band of the ultraviolet spectrum for solutions of phenol in cyclohexane. (For band nomenclature used, see previous parts of this series.) We have verified von I<eussler's results and have also investigated the corresponding spectral changes in both the B-band and the C-band for a nuinber of phenols, and for anisole. The rclevailt clata are listed in Table I. Table I and also Ito's recently obtained values for the C-bancls of phenol and anisole (3) shorn that only phenol and certain allcyl-substituted phenols give rise to appreciable spectral changes in the C-band and this suggests that the spectral changes are caused by interillolecular hydrogen bonding between phenol molecules. T h e relevant spectral curves are shown in Fig. 1. The ultraviolet d a t a in this way confirm the well-l;nown fact that phenol forms ail intermolecular hydrogen bond with other phenol molecules, and inciclentally that this bond is weaker than the intermolecular hydrogen bond between benzoic acid molecules since greater solute concentrations arc requil-ed for the phenol solutions before a concentration dependence is observed. This conclusion has frequently been deduced from other spectral clata ~vhich indicate that phenol molecules associate by means of hydrogen bollding to forin dimers, trimers, and even polymers with the clegree of associatio~l JiVIanzlscribt rccei~~ed Febrztary 16, 1960. ~ontribzttio~z from the

Spectroscopic Studies of Alcohols: Ii. The Conformation of 2-Haloethanols in Carbon Tetrachloride Solution

“…On the basis of n.m.r, spectroscopy Allan and Reeves (21) suggest that the flourine atom is too small to lead to measurable stability of a cis-isomer in o-fluorophenol. Similarly, the ultraviolet spectra of the B-bands of o-fluorophenol (22) and o-fluorobenzoic acid (23) indicate the absence of strong intramolecular hydrogen bonds in these compounds. However, these examples are not strictly analogous t o the gauche form of FCH2CH20H since the benzene ring modifies the character of the F atoin and the OH group.…”

Structure of Ammonium/Phenoxide Ion-Pairs in Solution

“…By far the greatest number of such studies have involved physical−chemical determinations of association constants, spectral perturbations, enthalpy changes, etc. in systems where hydrogen-bonding, not proton-transfer, predominates. − Proton-transfer to aliphatic amines has been shown to occur, however, with sufficiently acidic phenols dissolved in more polar solvents. , For example, 2-chlorophenol and pentachlorophenol in acetonitrile lose 6% and 100% of their protons, respectively, to n -propylamine . Our work has a different slant from most of that in the past.…”

“…in systems where hydrogen-bonding, not proton-transfer, predominates. [2][3][4][5][6][7][8] Proton-transfer to aliphatic amines has been shown to occur, however, with sufficiently acidic phenols dissolved in more polar solvents. 9,10 For example, 2-chlorophenol and pentachlorophenol in acetonitrile lose 6% and 100% of their protons, respectively, to n-propylamine.…”

Solvatochromism and potentiometic studies of some active nitroso- and nitroso-azo- compounds

“…The extra - * transition at 204-257 nm in hydrogen bonding solvents (e.g. ethanol, methanol and H2O) is due to the presence of an external hydrogen bond affecting the K band [40]. The slight shift of max of the electronic spectral bands from alcohol (EtOH or MeOH) to H2O, Table 2, depicts the presence of an internal hydrogen bond [41], affected by the interaction with nelectrons blocked by the solvent leading to an increased localization of electrons.…”