Gas-phase eliminations. Part VIII. The effect of β-methylation on the pyrolysis of some t-alkyl chlorides

The thermal unimolecular decompositions of C2H5Cl, i‐C3H7Cl, and t‐C4H9Cl

“…The equation k, = 1013.93*0.14 exp( -(45.7 f 0.4)kcal/mole/ RT)sec-*) has been derived from the measurements at 10 torr. The values of the Arrhenius parameters are nearly identical with those found in the hightemperature study of Tsang [20] (k, = 1013.9 exp( -46.2 kcal/mole/RT)sec-l) and in the low-temperature studies performed by Maccoll and Wong [21] (k, = Holbrook and Marsh [5] reported pl/z = 2.8 torr at incorrect. We conclude that the high-pressure region was covered by our measurements at 10 torr, since the rate constant was unaffected by lowering the initial pressure to 3 torr even at the highest temperature involved.…”

Isomerization of Neopentyl Chloride and Neopentyl Bromide by a 1,2-Interchange of a Halogen Atom and a Methyl Group

“…Thus, the thermal and chemical activation experiments are in fundamental agreement for the threshold energy of the CH 3 /Cl interchange reaction in neopentyl chloride. The calculated pre-exponential factor in Arrhenius form is 6.7 × 10 14 s −1 , which is 2.5 times larger than the upper limit of the experimental result, − , A = 2.5 × 10 14 s −1 . The large pre-exponential factor is a consequence of the low bending vibrational frequencies associated with the weakly bound Cl and CH 3 groups of the transition state.…”

“…The reaction path degeneracies favor 1,2-HCl by a factor of 3, but the 3,2-HCl elimination channel must have a slightly lower E 0 . In fact, 3,2-HCl elimination to give 2-methyl-2-butene was favored in pyrolysis of 2-chloro-2-methyl-butane, 8 which also suggests that the E 0 is lower for 3,2-HCl elimination than for 1,2-HCl elimination. This is supported by the DFT calculations of the threshold energies that give E 0 (1,2-HCl) ) 41.4 kcal mol -1 and E 0 (3,2-HCl) ) 40.4 kcal mol -1 , although the absolute values are too low, see the Supporting Information.…”

“…Reaction is exothermic by about 2 kcal mol −1 ; thus, 2-methyl-2-chlorobutane acquires an additional 2 kcal mol −1 of energy during the interchange in reaction . The threshold energy, E 0 , for the interchange reaction is ≈60 kcal mol −1 , based on our electronic structure calculations and the thermal activation studies of neopentyl chloride, whereas those for HCl elimination, reactions a and b, are ≈45 kcal mol −1 according to pyrolysis studies of 2-methyl-2-chlorobutane. Thus, the rearrangement process in is the rate-limiting step for all forms of activation of neopentyl chloride (or bromide) molecules.…”

“…The Cl/F, Br/Cl, and Br/F interchange reactions for haloalkanes with halogen atoms located on adjacent carbon atoms have been demonstrated and characterized in a series of recent studies from this laboratory. − These interchange reactions, which often are in competition with hydrogen halide elimination reactions, have threshold energies for dihaloethanes ranging from 43 (Br/Cl) to 60 (Cl/F) − kcal mol −1 . The Cl/methyl group and Br/methyl group interchange reactions are members of this genre of unimolecular reaction.…”