Bromination of fluoro-alkanes. Part 3.—Methane, fluoroform and fluoro-ethanes

The competitive brominations of the following compounds have been studied in the vapour phase: CH4, CF3H, C2H6, C2H5F, CH3CHF2, CH3CF3, CF3CH2F, CF2HCF2H and n-C3F7H. Arrhenius parameters have been obtained for all observed reactions involving abstraction of H by Br. Our previous result that D(CF3—H)–D(CH3—H)= 2.2±0.5 kcal mole–1 is confirmed and it is recommended that D(CF3—H)= 106.0 kcal mole–1 at 298°K. Upper limits are given for C—H bond dissociation energies in the other fluoroalkanes studied. Fluorine atoms attached to a given carbon atom have relatively little effect on abstraction of H from that carbon atom but the hydrogen atoms on the adjacent carbon atom are greatly de-activated. The reasons for this are discussed.