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The regioselectivity of deuterium (D) atom addition to 1-butene and 1-pentene monolayers adsorbed on the (100) surface of copper at 100 K was explained. It was previously established that hydrogen atoms intruding from the gas phase were capable of reacting with monolayer olefin molecules adsorbed on metal surfaces. It was revealed that the 2-butyl groups were the predominant product generated and formed in a D addition to terminal carbons of surface-bound butene molecules.

Monolayers of pure hydrocarbon fragments, generated and isolated at cryogenic temperatures, are intermediates in heterogeneous catalysis. The focus of attention shifted through time from highly dehydrogenated stable fragments to highly dehydrogenated reactive species, such as surface alkyls. Isolation of high coverages of these species enables the identification of fundamental reaction steps, such as beta-hydride elimination.

The alkyl, cycloalkyl and 2-bicyclo(2.2.1)heptyl bromides undergo 1,2-elimination of hydrogen bromide on heating below 250 Kelvin, on a Cu(100) surface to form the respective alkene. The reaction follows a two-step mechanism with initial cleavage of C-Br bond and then beta-hydride elimination. The rates of bond scission are the same for the different alkyls, but the elimination rates differ by several magnitude orders. The ring strain and planarity influence the transition state of the reaction.

The Ulmann coupling of iodobenzene in adsorbed monolayers occurs on single crystal Cu(111) surfaces when the surface is studied under ultrahigh-vacuum (UHV) conditions. Biphenyl is formed after dissociation of iodobenzene and results in the coupling of the absorbed phenyl groups which are formed. The phenyl groups also couple with iodobenzene molecules under high-coverage low-temperatures. High surface coverage exhibits a low-temperature pathway due to the bonding of the phenyl radicals to the surface of the copper.

Surface-bound alkyls go through beta-hydride removal above roughly 200 Kelvin. The thermal chemistry of these alkyl iodides at increased surface coverage is explored with temperature-programmed reaction/desorption to reveal the surface reaction products and reaction kinetics. There is a formation of alkyl coupling and disproportionation products at the temperature where the C-I bond delinks. The relative yields of these products indicate a radical mechanism. The parallel reaction channels for forming alkyl radicals and absorbed alkyls during C-I bond dissociation on the Cu (111) surface are examined in the context of analogous reactions of alkyl halides with metal surfaces in solution.

A study on the oxidative addition of iodomethane to a single-crystal Cu(111) surface under ultra-high-vacuum conditions is discussed. Evidence for the evolution of methyl radicals during this process is presented. Methyl radical ejection was detected by mass spectrometry during the thermal dissociation of the carbon-iodine bond in CH3I on the Cu(111) surface. An activation energy value for C-I bond scission was calculated as 8.5 kcal/mol with reaction temperature as 140 degrees Kelvin and a first-order preexponential factor of 10(super 13) s-1.

Temperature-programmed desorption was used to study the adsorption and thermal decomposition of 1-iodopropane on Cu(110). Results show that iodopropane adsorption on the surface is intact at 100 K. It starts to dissociate when the surface temperature is raised to 110 K. It then forms adsorbed propyl groups which orient with the C3v axis of the methyl group along the surface normal.

The structure of benzene deposited on a Cu(111) surface has been investigated by a combination of temperature-programmed desorption (TPD), high-resolution electron energy loss spectroscopy (HREELS), and near-edge x-ray absorption fine structure (NEXAFS) measurements. The results indicate that benzene forms a stable bilayer on Cu(111) at 110 K prior to multilayer formation. The TPD studies show that the second layer benzene desorbs with a peak temperature 5 K higher than that for benzene multilayers. HREELS and NEXAFS results indicate that benzene in the first layer bonds with its π ring parallel to the surface. With increasing coverage, benzene forms a second layer with its π ring significantly tilted away from the surface. The results are consistent with an approximately perpendicular configuration between the first and second layer benzene molecules, which is analogous to the structure of crystalline benzene. Isotope labeling experiments indicate there is almost complete mixing between molecules in different layers during sequential adsorption at 110 K. [ABSTRACT FROM AUTHOR]

Discusses many of the distinctions that chemists draw between theoretical chemistry and descriptive chemistry, along with the tendency for chemical educators to adopt the type of chemistry they feel is most important to teach. Uses examples to argue that theoretical chemistry and descriptive chemistry are, at the bottom line, the same. (TW)