Molecular structure and conformational equilibrium of vinylcyclopropane studied by gas phase electron diffraction

Conformation and geometry of cyclopropane rings having π-acceptor substituents: a theoretical and database study

“…Thus there is a symmetry-related g 0 conformer at ' À50 , with a g-g 0 rotational barrier of 9.4 kJ mol À1 at = 0 , so that the cis-bisected conformation is significantly disfavoured. These data for vinylcyclopropane agree well with spectroscopic and gas-phase structural studies, and also with the ab initio (MP2) and DFT calculations presented by de Meijere & Lü ttke (1969), Klahn & Dyczmons (1985), Traetteberg et al (1988), Shen & Traetteberg (2003) and Durig et al (2005). The gas-phase electron diffraction study of Traetteberg et al (1988) 3percentage ratio and a gauche local energy minimum of 4.96 kJ mol À1 from vibrational spectroscopy.…”

“…Again, the 29 substructures in the energetically disfavoured region, = 90-150 are all examples of multiply substituted rings, and often have additional R substituents in vinyl groups of the form -C(R or H) C(R or H) 2 , which must then compete sterically with other gem or vic substituents on the cyclopropane ring. If we eliminate these 29 substructures from the calculation of the trans:gauche percentage ratio, then 71% of the remaining 160 general vinyl substituents are trans, and 29% are gauche: a result which is comparable to the 77:23% ratio indicated by gas-phase electron diffraction (Traetteberg et al, 1988) and to the 79 (3):21 (3)% ratio from vibrational spectroscopy (Durig et al, 2005).…”

“…This is exemplified by recent theoretical studies of cyclopropanecarboxylic acid and related compounds (Badawi et al, 1998(Badawi et al, , 2008, carried out to explain their vibrational spectra, and similar computational studies associated with gas-phase electron diffraction (e.g. Traetteberg et al, 1988;Shen & Traettberg, 2003) or spectroscopic analyses (e.g. Durig et al, 2005).…”

“…Also in our calculations the gauche local energy minimum occurs at = 48.6 rather than the archetypal gauche torsion angle of 60 . This computed value may be compared with values from gas-phase electron diffraction (Traetteberg et al, 1988), where three least-squares intensity analyses making different geometrical assumptions gave values of 56.0 (6.4), 55.4 (6.4) and 51.8 (6.4) , although ab initio values of 62.2 and 61.4 are reported by Klahn & Dyczmons (1985) and Durig et al (2005). Fig.…”

Thermal isomerizations of vinylcyclopropanes to cyclopentenes

“…X -H torsional angle for the gauche conformer is 56Њ experimentally 82 and 62.2Њ according to ab initio calculations. and bicyclo 3.2.0 hept-2-enes are initiated by carbon᎐carbon bond cleavage; when the bond is essentially broken torsion changes may become significant.…”