Structure of cis,trans-1,4-Difluorobutadiene from Microwave Spectroscopy

Abstract

Microwave spectra in the 5.5−17.5-GHz region have been observed for cis,trans-1,4-difluorobutadiene, for its 13C isotopomers in natural abundance, for the four singly substituted deuterium isotopomers, and for the 1,4-d 2 species. For the parent species fitting 37 lines to a Watson-type Hamiltonian with the five quartic centrifugal distortion constants gave A = 12 988.333(1), B = 1467.8791(3), and C = 1318.5845(3) MHz. Stark effect measurements on three transitions of the parent species gave a dipole moment of 2.309(5) D with components μ a = 0.660(4) D and μ b = 2.213(5) D. Surprisingly, the B rotational constant for the 2-d 1 isotopomer, as indexed from the trans end, is larger than that for the normal species, and the rotational constants for the 3-d 1 isotopomer are also anomalous. Nonetheless, a complete, 17-parameter structure is proposed for this planar molecule and compared with density functional theory predictions made with the adiabatic connection method. Structural parameters are also compared with those of butadiene itself.

Length‐dependence of electron transfer coupling matrix in polyene wires: Ab initio molecular orbital theory study

“…The calculated geometry of the neutral molecule and its cation along with the values of V DA obtained from the two approaches are listed in Table II. For comparison, available theoretical [32][33][34] and experimental [35] values of the geometry of 1,3-trans-butadiene are also listed in the table. As can be seen, the calculated bond distance and bond angles are in good agreement with the available experimental and calculated data.…”

Rotational analysis of bands in the high-resolution infrared spectra of the three species of butadiene-1,4-d2; refinement of the assignments of the vibrational fundamentals

“…Available structural data suggest that the CAC bond length is 1.468 Å [2][3][4], which is close to the estimate of 1.470 Å for an sp 2 -sp 2 single bond length [1] but longer than recent results of quantum chemical calculations. These calculations give values that range from 1.450 to 1.456 Å [1,5]. Experimental data indicate that the C‚C bond length may be 1.348 Å [2,3] or 1.337 Å [4] and thus may or may not be appreciably longer than the double bond length of 1.332 Å of ethylene [6].…”

“…Experimental data indicate that the C‚C bond length may be 1.348 Å [2,3] or 1.337 Å [4] and thus may or may not be appreciably longer than the double bond length of 1.332 Å of ethylene [6]. Calculated values for the C‚C bond range from 1.333 to 1.346 Å [1,5]. Thus, it is not possible to discern evidence for p-electron delocalization from existing experimental data on CC bond lengths in BDE, and computational results are ambiguous.…”

“…The synthesis of BDE-c,c-d 2 made use of the regio-and stereospecific exchange of the protons in 1,4-dichlorobutadiene in basic D 2 O. In 1,4-dichlorobutadiene this exchange is limited to the 1,4-hydrogen atoms in contrast to the exchange with 1,4-difluorobutadiene [5], in which the 2,3-hydrogen atoms also exchange to some extent.…”

High-resolution infrared spectra of the two nonpolar isomers of 1,4-difluorobutadiene

“…A preliminary semi-experimental equilibrium structure of the polar cis,trans isomer was determined from a combination of ground state rotational constants obtained in a microwave investigation and quantum chemical calculations [4,5]. The nonpolar trans,trans and cis,cis isomers are microwave silent and must be investigated by high-resolution infrared spectroscopy.…”