Conformational stability from temperature dependent FT-IR spectra of liquid rare gas solutions, barriers to internal rotation, vibrational assignment, structural parameters and ab initio calculations for 3-bromopropene
Dt. Durig et Z. Yu, Conformational stability from temperature dependent FT-IR spectra of liquid rare gas solutions, barriers to internal rotation, vibrational assignment, structural parameters and ab initio calculations for 3-bromopropene, J MOL STRUC, 550, 2000, pp. 481-493
The infrared spectra of 3-bromopropene (allyl bromide), CH2=CHCH2Br, dissol
ved in liquid krypton (- 110 to - 155 degrees C) and liquid xenon (- 55 to
- 10 degrees C) at concentrations of about 1 x 10(-2) M are reponed. The te
mperature dependence of the infrared spectra of three conformer pairs in th
e xenon solution has been used to obtain an enthalpy difference of 184 +/-
12 cm(-1) (2.20 +/- 0.14 kJ/mol) with the gauche conformer the more stable
rotamer. Utilizing the asymmetric torsional fundamental of the ris conforme
r at 133 cm(-1) along with two accompanying hot bands, the gauche fundament
al at 99 cm(-1), the enthalpy difference of 184 cm(-1), and the gauche dihe
dral angle (BrCCC) of 116.1 degrees, the potential function governing the c
onformational interchange has been determined. The cis to gauche and gauche
to gauche barriers have been determined to be 707 and 848 cm(-1) respectiv
ely. The adjusted r(0) structural parameters have been obtained from the pr
eviously reported rotational constants and ab initio predicted values. The
conformational stability and infrared intensities, along with the vibration
al frequencies and structural parameters have been obtained from ab initio
calculations. These data are compared to the corresponding experimental qua
ntities when appropriate. A complete vibrational assignment is proposed for
the gauche conformer and most of the fundamentals have been assigned for t
he cis conformer. The overall results are compared and contrasted to those
for some similar molecules. (C) 2000 Elsevier Science B.V. All rights reser
ved.