1184-59-4Relevant articles and documents
Low-Temperature Decomposition of Alkyl Iodides on Ni(100) Surfaces: Evidence for the Formation of Alkyl Free Radicals
Zaera, Francisco,Tjandra, Sariwan
, p. 3044 - 3049 (1994)
Previous studies have shown that alkyl iodides dissociate on metal substrates around 200 K to produce iodine atoms alkyl moieties on the surface; here we report a new low-temperature decomposition pathway for those compounds on Ni(100) that leads to the formation of a close to 1:1 alkane-alkene mixture below 150 K.This latter reactions is proposed to occur via a mechanism where alkyl iodide dissociation results in the direct formation of free radicals.A combination of thermal desorption experiments with isotope labeling and hydrogen coadsorption was used to establish the importance of the nickel surface in the overall process and to rule out either surface disproportionation or gas-phase reactions as the source of the low-temperature products.Evidence was also obtained for a possible rearrangement of the adsorbed alkyl iodide molecules from a fat geometry into an upright configuration at high coverages, a change that would explain the ease with which the radicals formed after C-I bond scission are released into the gas phase instead of being left on the surface as adsorbed alkyl surface moieties.A comparison with other systems is also presented.
Deuterium kinetic isotope effects on the thermal isomerizations of deuteriocyclopropane to deuterium-labeled propenes
Baldwin, John E.,Singer, Stephanie R.
, p. 1510 - 1515 (2007/10/03)
The gas-phase thermal isomerizations of deuteriocyclopropane to the four possible monodeuterium-labeled propenes have been followed at 435°C. The observed distribution of products provides estimates of two deuterium kinetic isotope effects, the secondary ksh/ks D for the carbon-carbon bond cleavage leading to trimethylene diradical reactive intermediates and the primary kp h/kpD ratio for a [1,2] shift of a hydrogen or deuterium leading from the diradical to a labeled propene. The values determined are ksD/ksD = 1.09 ± 0.03 and kpH/kpD = 1.55 ± 0.06. The experimental ksD/ksD value found agrees well with some, but not all, earlier calculated values and conjectures.
Effects of Surface Defects and Coadsorbed Iodine on the Chemistry of Alkyl Groups on Copper Surfaces: Evidence for a Cage Effect
Jenks, Cynthia J.,Paul, Anumita,Smoliar, Laura A.,Bent, Brian E.
, p. 572 - 578 (2007/10/02)
The effects of defect sites and coadsorbed iodine atoms on the chemistry of alkyl groups with two to four carbon atoms on copper surfaces have been studied by temparature-programmed reaction (TPR).The primary reaction pathway for the adsorbed alkyl group both in the presence and absence of defects and iodine atoms is β-hydride elimination.Because desorption is not (under most conditions) the rate-determining step in the evolution of the product from the surface, the rate of the surface β-hydride elimination reaction could be monitored by TPR.Neither surface defects nor low coverages of coadsorbed iodine significantly affect the β-elimination rate.For high coverages of iodine, however, the rate of β-elimination by 5-10percent of the adsorbed alkyl groups is decreased by over five orders of magnitude (Trxn = 385 K versus 230 K).The reaction kinetics together with observations from low-energy electron diffraction studies suggest that the dramatic inhibition of the β-elimination rate for high iodine coverages is due to cages of immobile iodine atoms that surround the alkyl groups and prohibit hydrogen transfer to the surface.
