Association and the assignment of the OH overtones in hydrogen bonded alcohols

Abstract

The long-standing problem of the assignment of the first overtone of the OH stretching vibration of hydrogen bonded alcohols is examined for the cases of methanol, ethanol, and tertiary butanol. The spectra of the related deuterated alcohols were measured and isotopic isolation experiments were carried out at temperatures ranging from 25° to − 190°C. Dilute solutions were studied as well as the pure liquids. For the latter the second overtones were also measured. The first OH overtones, although overlapped by CH + OH combination bands were definitely identified and the anharmonicity constants were determined. They show a moderate but appreciable increase with respect to free OH stretching vibrations. Bands due to simultaneous excitation or coupling of two contiguous OH groups bound together by hydrogen bonds are also present.

Molecular structures and stratification in a 2-butanol—water system

“…In pure 2-butanol (Fig. 2), the intensity of the 0.96-µm band is very low, which fits in with the concept of alcohols as highly associated liquids.In accordance with the results of investigations of the overtones of methanol and butanol, the band of free O-H groups is found at 10,440 cm -1 (0.960 µm) for methanol and at 10,320 cm -1 (0.968 µm) for tert-butanol [7]. Pauling [8] points to the band of free O-H vibrations in methanol at 10,440 cm -1 and emphasizes its small width.…”

“…Our assignments for the bands of the second overtone of the O-H stretching vibration of 2-butanol do not contradict the similar results for different associated forms of other monatomic alcohols, which were obtained in [7,8,[12][13][14].…”

Hydrogen bonding of n-alcohols of different chain lengths

“…While in the fundamental region the polymer band is much more intense than the free band, in the overtone region the opposite usually holds (18)(19)(20). The reasons for this were the object of previous studies (21).…”

“…order to assign the overtones for the H-bonded OH groups (20). For all these reasons only the free band was used in the work reported here.…”

Mechanical and electrical anharmonicities of the linear hydrogen cyanide H-bonded trimer

“….HX, X = F, C1, from the measured overtones and combination bands. Also, the influence of mechanical and electrical anharmonicity on the intensity of X-H stretching vibrations (X = 0 or N in the most important cases) along with frequency and intensity of overtone bands, on the basis of the experimentally measured spectra, has been investigated (3)(4)(5)(6)(7).…”