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. Can. J. Chem. 61, 1924 (1983). The far-infrared spectra in the region of 50-450 cm-' are reported for the vapours of cyclohexanone and the structurally related compounds tetrahydro-4H-pyran-4-one, tetrahydro-4H-thiopyran-4-one. tetrahydro-4H-pyran-3-one, 1,3-dioxan-5-one, and 4H-pyran-4-one. Except for the last mentioned, the spectra are characterized by two or in some cases three sequences of Q branches which are assigned to the out-of-plane deformations of the cyclohexanone ring. 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. Each sequence is amenable to solution by a one-dimensional Hamiltonian incorporating a quadratic-quartic potential function, providing estimates for the magnitudes of the barriers to planarity. TRACY L. SMITHSON, NAN IBRAHIM et HAL WIESER. Can. J. Chem. 61, 1924Chem. 61, (1983 On rapporte les spectres dans I'infrarouge lointain (region de 50 h 450 em ') des vapeurs de cyclohexano~le et des composCs structur~llement apparent&: la tktrahydro-4H-pyranone-4. la tetrahydro 4H-thiopyranone-4, la tktrahydro 4~-~~r a n o n e -3 , la dioxane-1,3 one-5 et la 4H-pyranone-4. A l'exception du dernier compose, les spectres sont caracterises par deux ou, dans certain cas, trois sequences de Q raies que I'on attribue aux d6formations hors plan du cycle de la cyclohexanone. On pense que la sequence ayant la plus faible longueur d'onde dans chaque compose, provient d'une vibration qui si elle est cornpl6te transformerait la conformation chaise en son equivalent via une inversion en passant par la forme plane. Chaque sequencc peut Etre risolue par un Hamiltonien unidimensionncl impliquant une fonction de potentiel quadratique-quartique ct fournit ainsi des Cvaluations de I'ordre de grandeur des barrikres B la plan6aritC.[Traduit par le journal]

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The far-infrared spectra of 2-cyclohexene-1-one around 100 cm−1 is discissed and frequency assignments are considered, that are different from those of ref 2. (AIP)

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