Methylenecyclohexenes: inversion barriers from the far-infrared spectra

1983 ◽  
Vol 61 (3) ◽  
pp. 442-453 ◽  
Author(s):  
Tracy L. Smithson ◽  
Nan Ibrahim ◽  
Hal Wieser
Keyword(s):  
Infrared Spectra ◽  
Far Infrared ◽  
Ring Inversion ◽  
One Dimensional ◽  
Quartic Potential ◽  
Cyclohexene Ring ◽  
Out Of Plane ◽  
Type Band ◽  
Far Infrared Spectra ◽  
Plane Deformations

The far-infrared spectra of 3-methylenecyclohexene, 4-methylenecyclohexene, and 1-methyl-3-methylenecyclohexene in the region of 80–400 cm−1 are reported and interpreted mainly with a view to the two lowest out-of-plane deformations of the cyclohexene ring. Typical C-type band sequences are observed and interpreted in terms of ring inversion modes. Barriers to inversion are determined by means of a one-dimensional Hamiltonian with a quadratic-quartic potential function. Possible ground state geometries and forms of the inversion coordinates are discussed and compared to those thought to occur in the analogous cyclohexenones.

The far-infrared spectra and the ring inversion vibrations of a series of methylenecyclohexanes

1984 ◽  
Vol 62 (8) ◽  
pp. 1565-1572 ◽  
Author(s):  
Hal Wieser ◽  
Tracy L. Smithson ◽  
Nan Ibrahim ◽  
Peter J. Krueger
Keyword(s):  
Infrared Spectra ◽  
Far Infrared ◽  
Chair Conformation ◽  
Ring Inversion ◽  
One Dimensional ◽  
Planar Form ◽  
Out Of Plane ◽  
Minimum Potential ◽  
Related Compounds ◽  
Far Infrared Spectra

The far-infrared spectra in the region of 50 to 400 cm−1 are reported for the vapours of methylenecyclohexane and the related compounds 4-methylenetetrahydro-4H-pyran, 4-methylenetetrahydro-4H-thiopyran and 3-methylenetetrahydro-4H-pyran. The absorptions are assigned to the three out-of-plane deformations of the six-membered rings. The observed series of Q branches are ascribed to combination sequences involving the three modes. The lowest wavenumber sequence in each compound is believed to arise from a vibration which if completely executed would take the chair conformation to its equivalent via an inversion through the planar form. With the use of a one-dimensional Hamiltonian incorporating a quadratic-quartic double minimum potential function, barriers to planarity for the rings are estimated. The similarities between these compounds and the corresponding ketones are discussed.

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