William M. Stigliani

Microwave spectrum, structure and dipole moment of phenylacetylene

The microwave spectra of phenylacetylene, C6H5CCH, the deuterated species, C6H5CCD, and carbon–13 species at positions C(2), C(3), C(4), C(7) and C(8) have been measured and analysed. Inertial defects confirm the expected planarity of the molecule, and pronounced nuclear spin effects in the ground-state and vibrationally excited spectra confirm the C2v symmetry. The detailed structure is determined to be: C(1)C(2)= 1.388, C(2)C(3)= 1.396, C(3)C(4)= 1.398, C(1)C(7)= 1.448, C(7)C(8)= 1.208, and C(8)H = 1.055 A; C(6)C(1)c(2)= 120.8°, C(1)C(2)C(3)= 119.8°, C(2)C(3)C(4)= 119.9° and C(3)C(4)C(5)= 119.9°. The dipole moment has been accurately determined using new Stark-effect technique to be µ=µa= 0.656 ± 0.005 D and is found to be smaller for the deuterated species by 0.010 ± 0.006 D.The effect of the acetylenic group on the structure of the benzene ring is quite small, as expected from results of microwave studies for other substituted benzenes, while the acetylenic parameters are close to those of methylacetylene. The dipole moment is also near to that of methylacetylene (and other alkyl acetylenes) and is taken to indicate that it arises essentially from a π-system polarisation of the acetylenic group as suggested by recent molecular orbital calculations.

Structure of cyclobutanone

The microwave spectra of the 18O and the α,α,α′,α′-tetradeuterated isotopic species of cyclobutanone have been investigated. Structural parameters determined are rCO = 1.204 ± 0.006 A, rCHα = 1.099 ± 0.003 A, ∠ HαCHα = 109.2 ± 1° with the methylene group tilted toward the carbonyl group by 4.6 ± 0.8°.

Microwave and low-frequency vibrational spectra of bullvalene

Abstract The microwave spectrum of bullvalene has been investigated in the region 18–40 GHz. In addition to transitions in the ground vibrational state, transitions arising from five excited vibrational states below 600 cm −1 have also been observed. A combination of microwave intensity measurements and infrared and Raman data has been utilized to assign these vibrations. Three of the vibrations are E -type modes at 241, 355, and 588 cm −1 . One is an A 1 -type mode at 445 cm −1 , and another is an A 2 -type at 266 cm −1 . The microwave spectrum indicates the presence of a first-order Coriolis interaction for the E modes at 241 and 588 cm −1 . The first-order Coriolis coupling constant q = 0.557 MHz for the 241 cm −1 vibration. The spectral results are consistent with C 3 v symmetry for bullvalene.