Vibrational overtone spectra of o-fluorophenol and the “anomalous” order of intramolecular hydrogen bonding strengths

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Vol. 68; no. 2; pp. 331 - 336
• Main Authors: John, Usha, Kuriakose, Sunny, Nair, K.P.R.
• Format: Journal Article
• Language: English
• Published: England Elsevier B.V 01-10-2007
• Subjects: Cis and trans conformers; Dimerization; Hydrogen Bonding; Intermolecular hydrogen bonds; Intramolecular hydrogen bonds; o-Fluorophenol; Overtone spectrum; Phenols - chemistry; Red-shifting hydrogen bonds; Spectrophotometry; Spectrophotometry, Infrared; Spectrophotometry, Ultraviolet; Stereoisomerism; o-Fluorophenol; Cis and trans conformers; Overtone spectrum; Intramolecular hydrogen bonds; Red-shifting hydrogen bonds; Intermolecular hydrogen bonds; Dimerization
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2006.11.040

The near infrared vibrational overtone absorption spectrum of liquid phase
o-fluorophenol is examined in the region Δ
v
=
2, 3 and 4. The OH frequencies are compared with that of
o-chlorophenol and phenol. Considering the relative electronegativities of all halogens, one might expect the order of intramolecular hydrogen bond strength for
o-fluorophenol to be the greatest among all halogenophenols. It is evident that
o-fluorophenol forms a weaker intramolecular hydrogen bond (an anomalous trend) contrary to that expected from relative electronegativities of halogens. The local mode mechanical frequency values and anharmonicity values obtained from fitting the overtones are analysed. Our observation is in agreement with the previous experimental as well as the recent theoretical vibrational analysis of halogenophenols using density functional theory (B3LYP). The overtone spectra of
o-fluorophenol in carbon tetrachloride in different concentrations are also examined. It is noted that the OH-red shift which arises due to the intermolecular bond formation between the
cis and
trans conformers of
o-fluorophenol (dimerization) increases with concentration.