On the Photographic Infra-red Spectrum of Methylacetylene (Allylene) and the C–C Single Bond Distance.

Abstract

In a series of investigations of the absorption spectra of simple polyatomic molecules in the photographic infra-red we have included methylacetylene (CH3C0H) for investigation because it seems interesting from two points of view: (1) As it was to bo expected that the molecule represents a symmetrical top its investigation could serve as a check on the theory of the rotational structure of symmetrical tops in general which, so far, in the photographic infra-red, had been rather unsatisfactory. (2) As all the other nuclear distances in the molecule except the C-C single bond distance were known from the investigation of other molecules, it was hoped to obtain an accurate value for the C-C single bond distance from the moment of inertia of methylacetylene, which can be determined spectroscopically. EXPERIMENTALThe absorption tubes, grating spectrograph, infra-red plates, etc. were the* same as in several previous investigations (10,11). The methylacetylene was prepared from propylene bromide and potassium hydroxide. QUALITATIVE DISCUSSION OF THE METHYLACETYLENE BAND AND OF THE STRUCTURE OF THE MOLECULEIn tht1 whole photographic infra-red up to 12,000 A.U. only one absorption band was found.

High resolution Raman spectroscopy of gases with laser sources. XIV—The pure rotational spectra of dimethylacetylene and dimethyldiacetylene

“…For DMA& the values of these constants are nearly identical to those obtained by fitting the data of Table 2 to Eqn. (1). The B and Dj values are therefore nearly coincident with the values plotted in Fig.…”

Heats, equilibrium constants, and free energies of formation of the acetylene hydrocarbons through the pentynes, to 1,500-degrees K

“…No important change appears permissible in the lengths of the C-C and C =C bonds, which have been determined with satisfactory accord from electron-diffraction measurements for methylacetylene and dimethylacetylene [8], and from spectroscopic measurements for methylacetylene [6,7]. The assignment of frequencies made by Crawford [9] appears to be satisfactory, as he has shown that the same potential constants reproduce the spectra of acetylene, methylacetylene, and dimethylacetylene.…”

“…The value selected for the larger moment of inertia of methylacetylene was 98.276 X 10-40 g cm 2 , derived from the mean of the values of Bo reported by Herzberg, et al [6], 0.28458 cm-l , and by Badger and Bauer [7], 0.28496 cm-l . This value of the moment of inertia and the values of 1.060, 1.11 , and 1.207 angstrom units for the lengths of the acetylenic C-H, the methyl C-H, and the acetylenic C=C, bonds, respectively, yield 1.462 angstrom units for the length of the C-C single bond in methylacetylene.…”

Bond Lengths of Dimethylacetylene as Determined by Gas Electron Diffraction

“…The so-called shrinkage effect15) should disappear in regard to the ra distances, which are obtained from rg by subtracting the perpendicular and centrifugal contributions:16) (1) Since the ra structure represents the thermal-average positions of constituent atoms,4) it corresponds to the equilibrium symmetry of the molecule. In other words, provided the molecular symmetry is known from spectroscopy, the number of distance parameters (ra) can be decreased by assuming the symmetry as a constraint.…”