Spectroscopic and theoretical studies on intramolecular OH-p hydrogen bonding in 4-substituted 2-allylphenols.
2-Allylphenol (1) constitutes a mixt. of conformers, in which an OH-p hydrogen bonded closed (1a) and open form (1b) can be distinguished. 4-Substituted 2-allyphenols (2-9) have been synthesized and investigated by theor. and spectroscopic methods. In 1-9, the energy and the structure of the hydrogen bonds show distinct variation with substituents. In the PE spectra of most compds., two ionizations can be distinguished which are related to the allylic p(C:C) orbitals of the two conformers a and b and differ in energy by DIP(C:C). Alternatively, DIP(C:C) can be detd. indirectly from comparison of the PE spectra of the resp. phenols and anisoles with the same substituents. DIP(C:C) values between 0.3 and 1.1 eV were found. Frequency shifts Dn(OH) of the O-H vibration in CHCl3 soln. were measured by IR spectroscopy. By means of correlation anal. of the relationship between the strength of the intramol. hydrogen bond, DIP(C:C), Dn(OH) values and substituent consts. it is established how substituents in 4-position affect the intramol. OH-p hydrogen bond. The investigations demonstrate that the DIP(C:C) data can be used as descriptors for this intramol. interaction.
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