Gas-phase thermal reactions of fluorine-18 atoms with cis-1-chloropropene and trans-1-chloropropene

Abstract

The gas-phase reactions of fluorine atoms with cis- and trans-1-chloropropene have been investigated with /sup 18/F atoms moderated to thermal energies after formation by the /sup 19/F(n,2n)/sup 18/F nuclear reaction in SF/sub 6/. Addition to the olefinic position occurs preferentially on the central carbon atom, with a terminal/central ratio of 0.46 +/- 0.03, in contrast to the terminal addition preferences > 1.3 found with propene and 3-chloropropene substrates. The observed cis/trans product ratios of CH/sub 3/CH=CH/sup 18/F after terminal addition to CH/sub 3/CH=CHCl and Cl loss were 1.93 +/- 0.10 from the cis substrate and 1.29 +/- 0.04 from the trans. These ratios are consistent with about 10% /sup 18/F/Cl substitution with retention of the substrate geometry before rotation can occur in the newly formed radical and 90% loss of Cl from a rotating radical giving an equilibrated product favoring the more stable cis product in the ratio of 1.65/1.0. The overall rate constant for reaction of fluorine with the cis- and trans-CH/sub 3/CH=CHCl substrates is about 1.5 x 10/sup -10/ cm/sup 3/ molecule/sup -1/ s/sup -1/ and approximately 1.0 x 10/sup -10/ cm/sup 3/ molecule/sup -1/ s/sup -1/ for the addition process by itself. The addition rate constant ismore » not significantly different than that for CH/sub 3/CH=CH/sub 2/, indicating that the lower yield of terminal addition with 1-chloropropene comes from internal directional preferences after bond-forming olefinic addition is already assured.« less