Symmetric Top Spectra Research Articles

ChemInform Abstract: THE MICROWAVE SPECTRUM, STRUCTURE, AND DIPOLE MOMENT OF CIS‐1,2,3‐TRIFLUOROCYCLOPROPANE

Abstract The microwave spectrum of cis-1,2,3-triflurocyclopropane has been investigated in the region 8–40 GHz. A fit of the oblate symmetric top spectrum gives a rotational constant of 4064.925 ± 0.022 MHz. A molecular structure was determined using the rotational constants obtained from assignments of the monodeutero species and the carbon-13 species. The molecular parameters are r (CH) = 1.095 ± 0.002 A , r (CC) = 1.507 ± 0.001 A , r (CF) = 1.354 ± 0.001 A and ∠(HCF) = 112.3 ± 0.2°. The dipole moment was determined to be 3.89 ± 0.02 D. The structural parameters are compared to other substituted cyclopropyl ring structures and to molecular orbital predictions as well as to related fluorocarbons. The molecule provides another example of the effect of fluorine substitutions on shortening adjacent bonds. It is also found that nonbonded F⋯F distances tend to be constant.

The microwave spectrum, structure, and dipole moment of cis-1,2,3-trifluorocyclopropane

The microwave spectrum of cis-1,2,3-triflurocyclopropane has been investigated in the region 8–40 GHz. A fit of the oblate symmetric top spectrum gives a rotational constant of 4064.925 ± 0.022 MHz. A molecular structure was determined using the rotational constants obtained from assignments of the monodeutero species and the carbon-13 species. The molecular parameters are r (CH) = 1.095 ± 0.002 A ̊ , r (CC) = 1.507 ± 0.001 A ̊ , r (CF) = 1.354 ± 0.001 A ̊ and ∠(HCF) = 112.3 ± 0.2°. The dipole moment was determined to be 3.89 ± 0.02 D. The structural parameters are compared to other substituted cyclopropyl ring structures and to molecular orbital predictions as well as to related fluorocarbons. The molecule provides another example of the effect of fluorine substitutions on shortening adjacent bonds. It is also found that nonbonded F⋯F distances tend to be constant.

Far infared spectra of prolate and oblate symmetric tops

A Fourier transform spectrometer has been used to measure the pure rotational spectra of some symmetrical top molecules in the range 10–60 cm −1. The spectra have been interpreted in terms of molecular rotational constants. Differences arise between prolate and oblate tops. In the former case (methyl halides, methyl cyanides, and methyl acetylenes) the spectra can be used fairly satisfactorily to derive the rotational constants B and D J , although allowance may have to be made in evaluating the data for the existence of superposed rotational spectra of vibrational states of low frequency. The data on oblate tops can be explained satisfactorily by taking into account the greater intensity of higher K components of J lines as J increases, and the unresolved nature of these groups of K components for a given J, so that the results are in good accord with values of the molecular constants derived from microwave spectroscopy. The spectrum of trimethylamine shows a series of lines at higher frequencies which are connected with transitions involving torsional energy levels in this molecule.