Intramolecular π-Type Hydrogen Bonding and Conformations of 3-Cyclopenten-1-ol. 2. Infrared and Raman Spectral Studies at High Temperatures

Abstract

The vapor-phase infrared and Raman spectra of 3-cyclopenten-1-ol (3CPOL) have been collected at temperatures ranging from 25 to 267 degrees C. These clearly show the presence of four conformations of 3CPOL with the one with intramolecular pi-type hydrogen bonding being most abundant. The spectra of all four conformations have been assigned, and these agree well with the computed values from the DFT calculation. The frequency shifts observed for the different conformations are in accord with the predicted values. In the O-H stretching region the conformer A with the pi-type intramolecular hydrogen bond has the lowest stretching frequency at 3623.4 cm(-1) while the three higher energy conformers have frequencies 14.2, 32.0, and 36 cm(-1) higher. In the C=C stretching region conformer A again has the lowest frequency at 1607.3 cm(-1) while the other conformers have bands 2.1, 8.0, and 13.4 cm(-1) lower. Both the O-H stretching and the C=C stretching force constants are decreased about 2% by the hydrogen bonding. Five of the other vibrations show significant predicted frequency shifts up to 193 cm(-1). Analysis of intensity data at different temperatures was used to calculate the energy difference between the two most stable conformers. This was found to be 435 +/- 160 cm(-1), and the result agrees reasonably well with the high level ab initio results which range from 274 to 401 cm(-1).

Femtisecond single-mole infrared spectroscopy of molecular clusters

“…129 The less subtle case of direct complexation of CQC bonds by hydride groups remains to be explored in the CQC-stretching fundamental range by pulsed jet-FTIR techniques, whereas it has been studied in the gas phase. 130,131 5 The fingerprint region An advantage of FTIR spectroscopy over laser-based techniques is that the fingerprint region is routinely available, whereas tabletop lasers are often restricted to selected narrow ranges. 56,132 In fact, the early work on clusters in the 10 mm range has been dominated by line-tuneable CO 2 lasers.…”

Soft hydrogen bonds to alkenes: the methanol–ethene prototype under experimental and theoretical scrutiny

“…Fixation of the donor and acceptor moieties in a common molecular frame is an alternative to increase the fraction of hydrogen-bonded structures, and O-H stretching red shis of up to 90 cm À1 have been found for various such intramolecular OH/p interactions in different environments. [5][6][7][8] However, it is difficult to elucidate the role that geometric strain and substituent effects have on the spectroscopic signatures in these cases. In contrast to aromatic OH complexes, [9][10][11][12] unconstrained olenic alcohol contacts remain surprisingly unexplored.…”

1H NMR study of the hetero‐association of unsaturated alcohols with pyridine

“…GED data show that the major conformer (50 ± 20%) in 4‐penten‐1‐ol, 3e , is that with the OH group close enough to the C = C bond for intramolecular OH/π interactions to occur . Likewise, 3‐cyclopenten‐1‐ol has four possible conformers, of which the lowest in energy, by about 5 kJ mol −1 , is intramolecularly hydrogen‐bonded . However, in no case is there a formal demonstration of the existence of IHB.…”