Vibrational spectra of some small-ring compounds

The synthesis of a series of structurally related deuterium-substituted small-ring hydrocarbons is reported. These include ethylene-(underlined "d"₂)-cyclobutane-(underlined "d"₆), methylene- (underlined "d"₂)-cyclobutane-2,3-(underlined "d"₂), methylenecyclobutane-2, 2, 3, 3-(underlined "d"₄), methylenecyclopentane-2, 2, 5, 5-"underlined "d"₄) and methylene- (underlined "d"₂)-cyclopentane-2, 2, 5, 5- (underlined "d"₄). The mid-infrared (4000-200 cm�¹) and raman spectra of methylenecyclobutane, methylene- (underlined "d"₂)-cyclobutane- (underlined "d"₆), methylenecyclopentane, methylenecyclopentane-2, 2, 5,5- (underlined "d"₄), and methylene- (underlined "d"₂)-cyclopentane-2, 2, 5, 5- (underlined "d"₄) are reported. The 32 fundamental frequencies of the methylenecyclobutane derivatives above 200 cm�¹ are assigned. Assignments are made on the basis of the ir gas-phase band cotours, polarization of Raman lines, relative intensities, comparison with the spectra of structurally related molecules and considerations of the molecular symmetry. From analysis of combination bands in the mid-infrared spectra of methylenecyclobutane and methylene- (underlined "d"₂)-cyclobutane-2, 2-(underlined "d"₂), the ring structure is found to be non-planar with a barrier of 168 ± 10 cm�¹ (~0.5 kcal/mole) t the planar conformation. Approximately forty observed frequencies are fit with two-para-meter potential-function in the ring-puckering coordinate, x (in [equation in PDF]), when the reduced mass ratio for the two derivatives is taken into account.