title: Bimolecular kinetic studies with high-temperature gas-phase 19F NMR: cycloaddition reactions of fluoroolefins.
abstract: A gas-phase NMR kinetic technique has been used for the first time to obtain accurate measurements of rate constants of some bimolecular, second-order cycloaddition reactions. As a test of the potential use of this technique for the study of second-order reactions, the rate constants and the activation parameters for the cyclodimerization reactions of chlorotrifluoroethylene (CTFE) and tetrafluoroethylene (TFE) were determined in the temperature range 240-340 degrees C, using a commercial high-temperature NMR probe. Obtaining excellent agreement of the results with published data, the technique was then applied to the reaction of 1,1-difluoroallene with 1,3-butadiene, the results of which indicate that the use of gas-phase NMR for reaction kinetics is particularly valuable when a reagent is available only in small amounts and in cases where there are several competing processes occurring simultaneously. The major processes observed in this reaction are regioselective [2+2] and [2+4] cycloadditions, whose rates and activation parameters were determined [k2 = 9.3 x 10(6) exp(-20.1 kcal x mol(-1)/RT) L/mol(-1) x s(-1) and k3 = 1.2 x 10(6) exp(-18.4 kcal x mol(-1)/RT) L/mol(-1) x s(-)(1), respectively] in the temperature range 130-210 degrees C.
authors.affiliation: Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA. Alexander.B.Shtarov@usa.dupont.com
authors.forename: A B
authors.initials: AB
authors.lastname: Shtarov
authors.forename: P J
authors.initials: PJ
authors.lastname: Krusic
authors.forename: B E
authors.initials: BE
authors.lastname: Smart
authors.forename: W R
authors.initials: WR
authors.lastname: Dolbier