Raman and infrared spectra, conformational stability, barriers to internal rotation, vibrational assignment and ab initio calculations of trans-1-chloro-2-butene

The results of ab initio SCF MO calculations at the Hartree-Fock (3-21G and 6-31G*) and DFT levels (B3LYP/6-31G*, B3LYP/6-311+ G**) for 5-Ñuoro-(5FP), 5-chloro-(5ClP) and 5-bromo-trans-penta-1,3-diene (5BrP) molecules and vibrational spectra (Raman and FTIR) of the corresponding liquid phases are reported and discussed. For the isolated systems, ab initio calculations at the B3LYP/6-311+ G** level yield the anti-skew conÐguration (rotations around the C2ÈC3 and C4ÈC5 bonds, respectively) as the most stable form for all the molecules considered in this study. The Raman spectra of the liquid samples show pairs of bands whose temperature-dependent intensities are ascribed to conformational equilibria. From the plot of logarithm of intensity ratio vs. inverse temperature, DH values of Ô 2 » 0.8, 1 » 0.3 and 1.5 » 0.2 kJ mol-1 were derived for 5FP, 5ClP and 5BrP, respectively, corresponding to anti-skew Ç anti-syn equilibria. Considering the Boltzmann populations at room temperature, the skew form is clearly the dominant one in all cases, except for 5FP in the liquid phase, where it shares approximately 50% of the population with the slightly more populated syn form. In addition, for 5ClP and 5BrP, the skew form is practically the only form to occur in the isolated molecule situation. In all cases, passing from the isolated molecules to the liquid phase has the e †ect of increasing the population of the syn form, a trend which is clearly more important for 5FP, where the latter form becomes barely dominant at room temperature.

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Conformational equilibria for 5-fluoro-, 5-chloro- and 5-bromo-trans-penta-1,3-diene: the effect of the halogen substituent

Marques

Ribeiro‐Claro

Teixeira‐Dias

1999

J. Raman Spectrosc.

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ChemInform Abstract: Raman and Infrared Spectra, Conformational Stability, Barriers to Internal Rotation, Vibrational Assignment and ab initio Calculations of trans‐1‐Chloro‐2‐butene.

Durig¹,

Costner²,

Wang³

et al. 1994

ChemInform

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Raman and infrared spectra, conformational stability, and ab initio calculations oftrans-1-fluoro-2-butene

Durig¹,

Herrebout²,

Qiu³

et al. 1996

Struct Chem

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The P, aman (3200 to 10 cm-i) and infrared (3200 to 20 cm-i) spectra of gaseous and solid trans-1-fluoro-2-butene, trans-CH3HC=CHCH2 F, have been recorded. Additionally, the Raman spectrum of the liquid with qualitative depolarization data has also been obtained. Variable temperature studies have been carried out with the sample dissolved in xenon. These spectral data have been interpreted on the basis that the molecule exists in the fluid phases as a mixture of the synclinal (fluorine atom oriented cis to the-double bond) and anticlinal (gauche) conformations and the synclinal conformer is more stable by 135 + 30 cm -I (377 + 106 cal/mol). There was a considerable scatter of the data but in the liquid state the anticlinal conformer is more stable and the only comformer present in the solid state. Ab initio gradient calculations employing the RHF/3-21G, PHF/6-31G*, and MP2/6-31G* basis sets predict the synclinal conformer to be more stable by 800, 86, and 150 cm -I, respectively. The fundamental asymmetric torsional mode for the synclinal comformer is observed at 123.9 cm -~ with three excited states falling to lower frequency. The corresponding mode for the anticlinal conformer is observed as a broad nondescript band centered at about 93 cm -I, Utilizing these data along with the AH and dihedral angle for the anticlinal conformer the potential function for the conformational interchange has been calculated. The determined coefficients are VI = -246 + 5, V 2 = 371 + 3, V 3 = 836 + 22, I/4 = 86 + 3, and V 6 = 85 + 8 cm-J. Complete equilibrium geometries for both conformers have been determined with the RHF/3-21 G, RHF/6-31G*, and MP2/6-31 G* basis sets. A normal coordinate analysis utilizing the harmonic force constants obtained with the MP2/6-3 IG* basis set has been carried out for both conformers. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.

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Raman and infrared spectra, conformational stability, barriers to internal rotation, vibrational assignment and ab initio calculations of trans-1-chloro-2-butene

Cited by 5 publications

References 36 publications

Conformational equilibria for 5-fluoro-, 5-chloro- and 5-bromo-trans-penta-1,3-diene: the effect of the halogen substituent

Conformational equilibria for 5-fluoro-, 5-chloro- and 5-bromo-trans-penta-1,3-diene: the effect of the halogen substituent

ChemInform Abstract: Raman and Infrared Spectra, Conformational Stability, Barriers to Internal Rotation, Vibrational Assignment and ab initio Calculations of trans‐1‐Chloro‐2‐butene.

Raman and infrared spectra, conformational stability, and ab initio calculations oftrans-1-fluoro-2-butene

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