Thermochemistry of phenols: quantification of theortho-,para-, andmeta-interactions in tert-alkyl substituted phenols

✍ Scribed by S.P. Verevkin

• Publisher: Elsevier Science
• Year: 1999
• Tongue: English
• Weight: 248 KB
• Volume: 31
• Category: Article
• ISSN: 0021-9614
• DOI: 10.1006/jcht.1998.0459

✦ Synopsis

The standard ( p o = 0.1 MPa) molar enthalpies of formation f H o m (l or cr) at T = 298.15 K were measured by means of combustion calorimetry for 2-tert-butylphenol, 2-tert-butyl-5methylphenol, 2-tert-butyl-4-methylphenol, 2,4-di-tert-butylphenol, 3-tert-butylphenol, 4tert-butylphenol, 2-methyl-4-tert-butylphenol, 4-tert-amylphenol, and 4-tert-octylphenol. The standard molar enthalpies of sublimation (or vaporization) of these compounds, and also of 2-tert-amylphenol, 2,4-di-tert-amylphenol, 2-tert-octylphenol, and 2,4-di-tert-octylphenol were obtained from the temperature dependence of the vapour pressure measured in a flow system. Molar enthalpies of fusion 1 cr H o m of the solid compounds were measured by d.s.c. Resulting values of f H o m (g) were obtained at T = 298.15 K and used to derive strain enthalpies of tert-alkylphenols. The intra-molecular interactions of the substituents were discussed in terms of deviations of f H o m (g) from the group additivity rules. The interaction energy of the tert-alkyl and OH groups in the gas phase was found to be 12.5 kJ • mol -1 for the ortho-interaction, 1.7 kJ • mol -1 for the para-interaction, and 2.6 kJ • mol -1 for the meta-interaction. These values provided a further improvement on the group-contribution methodology for estimation of the thermodynamic properties of organic compounds.