The infrared spectra and structure of acetylsalicylic acid (aspirin) and its oxyanion: an ab initio force field treatment

• Published in: Journal of molecular structure 1996, Vol.378 (3), p.189-197
• Main Authors: Binev, I.G., Stamboliyska, B.A., Binev, Y.I.
• Format: Article
• Language: English
• Subjects: Ab initio calculation; Acetylsalicylic acid; Infrared spectroscopy
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/0022-2860(95)09170-X

The structures of acetylsalicylic acid (aspirin) (I) and its oxyanion (II) have been studied by means of infrared spectra and ab initio 3–21 G force field calculations. The 3100-1100 cm −1 region bands of both the aspirin molecule and its oxyanion have been assigned. The theoretical infrared data for the free aspirin anion are in good agreement with the experimental data for aspirin alkali-metal salts in dimethyl sulfoxide- d 6. The theoretical geometrical parameters for the isolated aspirin molecule are close to the literature X-ray diffraction data for its dimer in the solid state, except for those of the carboxy group, which participates directly in hydrogen bond formation. The changes in both the spectral and geometrical parameters, caused by the conversion of the aspirin molecule into the anion, are essential, but they are localized mainly within the carboxy group and the adjacent C-Ph bond. This is also true for the changes in the corresponding bond indices and electronic charges.