Dielectric Studies. XXX. Complex Formation and Intramolecular Hydrogen Bond Fission in ortho-Substituted Phenols

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Abstract
Dielectric constant and loss factors of o‐nitrophenol, o‐chlorophenol, guaiacol, 2,6‐di‐tert‐butylphenol (DTBP), and 2,4‐dinitrophenetole in p‐xylene and o‐nitrophenol in cyclohexane, each solution containing a specified mole fraction of a powerful electron donor molecule, 1,4‐diazabicyclo‐2,2,2‐octane (DBO), have been determined at four or five microwave frequencies at 25°C. Consistent analyses into contributions from two Debye terms could not be obtained for any of the solutions except that of DTBP. The mean relaxation times, distribution coefficients, and dipole moments all show considerable changes compared with solutions of the same molecules not containing any DBO. The solutions of 2,4‐dinitrophenetole and DTBP are exceptions. The data can be explained by complexing of the DBO with the phenols via a hydrogen bond involving the hydroxyl hydrogen. Since the intermolecular hydrogen bond competes with the DBO for the hydrogen of the hydroxyl group a significant amount of complexing must correspond to rupture of a proportion of intramolecular hydrogen bonds even in the case of the o‐nitrophenol. The absence of complexing with 2,4‐dinitrophenetole, a highly polar molecule, shows that dipolar interactions are not important. Only weak interaction seems to occur with DTBP and DBO, and this may be attributed to the bulky tert‐butyl groups shielding the phenolic proton.