Molecular Force Fields of s-trans-1,3-Butadiene and the Second Stable Conformer

Abstract

Normal-coordinate analyses of s-trans-1,3-butadiene and its various deuterated and ¹³C-substituted analogs were performed using the group-coordinate force field, and a set of force constants was determined. The infrared spectra of the second stable conformer of 1,3-butadiene-d₀, -1,1,4,4-d₄, and -d₆ were analyzed on the basis of normalcoordinate calculations of the planar s-cis form and a nonplanar gauche form. Such an analysis suggests that the second stable conformer takes a gauche form rather than the s-cis. To increase the number of reliable data to be used in this study, the infrared and Raman spectra of the d₀, 1,1,4,4-d₄, and d₆ species were observed in low-temperature Ar matrices. The infrared spectra of the second stable conformer were also observed using a combination of the high-temperature nozzle and low-temperature matrix techniques.