Raman and infrared spectra, conformational stability, barriers to internal rotation, vibrational assignment, and ab initio calculations for 3‐iodopropene

Abstract

The Raman spectra (3200-10 cm-') of gaseous, liquid and solid and infrared spectra (3200-40 cm-') of gaseous and solid 3-iodopropene, H,C=CHCH,I, were recorded. The fundamental asymmetric torsional transition of the most stable gauche conformer was observed in the Raman and far-infrared spectra of the gas at 95 cm-l. In the Raman spectrum of the liquid a second C-I stretch and two skeletal bending modes were identified for the less stable cis conformer. From a study of the Raman spectrum of the liquid at various temperatures, a value of 648 f 81 cm-' (1.85 f 0.23 kcal mol-I) was determined for the enthalpy difference between the higher energy cis and preferred gauche conformers. These data, along with the dihedral angle for the gaucke conformer obtained from an electron difiaction study, combined with results obtained from ab initiu calculations, allow for an estimate of the potential function governing internal rotation about the C-C bond. The values for the torsional potentid coefficients are V , = -208 & 10, V , = -532 & 10, and V, = 534 f 8 cm-'. This potential is consistent with a dihedral angle ( L CCCI) of 113.0' for the gauche conformer cis to gauche, gauche to gauche and gauche to cis barriers of 160, 904 and 738 cm-', respectively, and an enthalpy difference between the conformers of 580 f 30 cm-' (1.66 f 0.09 kcal mol-'). The asymmetric torsional potential surface, complete equilibrium geometries and vibrational frequencies were calculated using restricted HartreeFock calculations with the STO-3G*, 3-2lG*/medium, a medium-sized combination basis set suitable for a DZ-type contraction of the valence shell orbitals, and the LANLlDZ basis sets. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.

Infrared and Raman Spectra, Conformational Stability, Ab Initio Calculations, and Vibrational Assignment of 1-Penten-4-yne

“…The structural parameters, conformational stability, and vibrational spectra of the 3-monosubstituted propenes, CH 2 CHCH 2 X, where X = F, , Cl, Br, , I, CN, CH 3 , SiH 3 , NH 2 , − OH, , etc., have been of interest for several years. For the 3-halopropenes (allyl halides) only the fluoride has the syn conformer as the more stable rotamer, but many of the ab initio calculations at the MP2 level with full electron correlation utilizing relatively large basis sets with diffuse functions predict the gauche conformer as the more stable form.…”

Raman and infrared spectra, conformational stability, vibrational assignment, and ab initio calculations of cis-1,3-dichloropropene

“…Our recent investigation~ have included the determination of the potential functions governing internal rotation about the ~( s p~) -~( s p ' ) bonds of the parent 3-halopropenes and some substituted derivatives (24)(25)(26)(27)(28)(29)(30)(31)(32). Ally1 fluoride (24)(25)(26), chloride (27), bromide (28,31), and iodide (32) have been determined to exist as a mixture of syn and gauche conformers, and for the fluoride we have shown that the conformer that has the halogen atom syn to the double bond is the more stable rotamer (24)(25)(26). For 3-chloropropene, the value of the energy difference (27) was inferred to be less than 100 cm-' (286 cal/mol) and the spectral data merely indicated a very slight preference for the syn conformer for the gaseous state.…”

“…For 3-chloropropene, the value of the energy difference (27) was inferred to be less than 100 cm-' (286 cal/mol) and the spectral data merely indicated a very slight preference for the syn conformer for the gaseous state. For allyl bromide (28,31) and iodide (32) the gauche structure is thermodynamically preferred.…”

“…Because an appreciable amount of a second higher energy conformer has been detected in the vibrational spectra of the 3-halopropenes (24-28, 3 1,32) and trans-1,3-dichloropropene (33), the possibility remains that a small amount of it may exist for cis-l,3-dichloropropene. Therefore, we have undertaken the present spectroscopic study to carry out a conformational analysis, based on the previously unreported vibrational spectra, and to perform ub initio calculations for comparison with the results obtained from molecular mechanics calculations (35).…”

Infrared and Raman spectra, conformational stability, ab initio calculations and vibrational assignment of 1-hexen-4-yne

“…The structural parameters, conformational stability, and vibrational spectra of the 3-monosubstituted propenes, CH 2 = CHCH 2 X, where X ¼ F, 1,2 Cl, 3 Br, 4,5 I, 6 CN, 7 CH 3 , 8 SiH 3 , 9 NH 2 , [10][11][12][13] OH, 14,15 C= =CH, 16 etc. have been of interest for many years.…”