title: Semiexperimental equilibrium structures for cis,cis- and trans,trans-1,4-difluorobutadiene by the mixed estimation method and definitive relative energies of the isomers.
abstract: Equilibrium molecular structures accurate to 0.001 Å and 0.2° have been determined for cis,cis- and trans,trans-1,4-difluorobutadiene by the semiexperimental mixed estimation method. In this method, structures are fitted concurrently to equilibrium rotational constants and bond parameters obtained from an intermediate level of electronic structure theory. The effect of fluorine substitution on the carbon backbone of butadiene is surprisingly small. Definitive energy differences for the ground states were computed, employing the focal-point analysis (FPA) technique, between the trans,trans and cis,cis isomers (ΔH°0 = 5.6(3) kJ mol(-1)) and the cis,trans and cis,cis isomers (ΔH°0 = 3.2(2) kJ mol(-1)) of 1,4-difluorobutadiene. These differences confirm the exceptional relationship that the trans,trans isomer has the highest energy and the cis,cis isomer the lowest energy, endorsing what was reported earlier on the basis of experimental observations in benzene solution.
authors.affiliation: Laboratoire de Physique des Lasers, Atomes et Molécules, Université de Lille 1 , 59655 Villeneuve d'Ascq Cedex, France.
authors.forename: Jean
authors.initials: J
authors.lastname: Demaison
authors.forename: Attila G
authors.initials: AG
authors.lastname: Császár
authors.forename: Peter
authors.initials: P
authors.lastname: Groner
authors.forename: Heinz Dieter
authors.initials: HD
authors.lastname: Rudolph
authors.forename: Norman C
authors.initials: NC
authors.lastname: Craig