1H–17O Nuclear-Quadrupole Double-Resonance Study of Hydrogen Disorder in 2-Nitrobenzoic Acid

✍ Scribed by M Torkar; V Žagar; J Seliger

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 95 KB
• Volume: 144
• Category: Article
• ISSN: 1090-7807
• DOI: 10.1006/jmre.2000.2051

✦ Synopsis

Temperature dependence of 17 O nuclear quadrupole resonance frequencies was measured in solid 2-nitrobenzoic acid by a 1 H-17 O nuclear quadrupole double resonance technique. The experimental results show the presence of a fast exchange of hydrogen atoms between two nonequivalent positions within the O-H . . . O hydrogen bonds. The hydrogen disorder is ascribed to concerted jumps of two hydrogen atoms within the hydrogen bonds connecting two molecules in a dimer. The energy difference ⌬E of the two hydrogen configurations is equal to ⌬E ‫؍‬ 60 meV ‫؍‬ 5.8 kJ/mol. The dipole structure of the 17 O NQR lines from the C-O-H oxygen positions was also measured at ؊100°C and at room temperature. The orientation of the principal axes of the electric field gradient tensor with respect to the O-H bond and the sign of the quadrupole coupling constant were determined. The oxygen-hydrogen distance R O-H , as determined from the dipole structure of the 17 O NQR lines is at ؊100°C equal to 0.099 nm. At room temperature we observe a longer distance, R O-H ‫؍‬ 0.101 nm, in agreement with the hydrogen intrabond exchange.