Activation of alkanes by Cr{sup +}: Unique reactivity of ground-state Cr{sup +}({sup 6}S) and thermochemistry of neutral and ionic chromium-carbon bonds

Journal Article · Wed Mar 11 04:00:00 EST 1992 · Journal of the American Chemical Society

DOI:https://doi.org/10.1021/ja00032a017· OSTI ID:232273

Fisher, E R; Armentrout, P B ^[1]

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1. Univ. of Utah, Salt Lake City, UT (United States)

Guided ion beam mass spectrometry is used to study the reactions of ground-state Cr{sup +}({sup 6}S) with propane, butane, methylpropane, dimethylpropane, and selectivity deuteriated propane and methylpropane. Thermal energy reactions of Cr{sup +}({sup 6}S) with 4-octyne are also investigated. Ground-state Cr{sup +} ions undergo no bimolecular reactions at thermal energies with any of the alkanes, but do react at elevated kinetic energies. The only products formed at thermal energy in the alkane systems are the collisionally stabilized adduct complexes. Approximate lifetimes for these adducts are determined. Analyses of the endothermic processes in the alkane systems yields 298 K bond energies for several chromium-ligand species. These include the neutral and ionic chromium methyl species [D{degrees}(Cr-CH{sub 3}) = 37.9 {+-} 2.0 kcal/mol and D{degrees}(Cr{sup +}-CH{sub 3}) = 30.3 {+-} 1.7 kcal/mol], several other chromium ion-alkyl species [D{degrees}(Cr{sup +}-C{sub 2}H{sub 5}) = 35.0 {+-} 2.1 kcal/mol, D{degrees}(Cr{sup +}-1-C{sub 3}H{sub 7}) = 32.1 {+-} 1.4 kcal/mol, D{degrees} (Cr{sup +}-2-C{sub 3}H{sub 7}) = 28.5 {+-} 1.3 kcal/mol], and chromium ion-vinyl and -various alkylidenes [D{degrees}(Cr{sup +}-C{sub 2}H{sub 3}) = 59.0 {+-} 2.3 kcal/mol, D{degrees}[Cr{sup +}=CHCH{sub 3}] = 52 {+-} 3 kcal/mol, D{degrees}[Cr{sup +}=CHCH{sub 2}CH{sub 3}] = 36 {+-} 3 kcal/mol, D{degrees}[Cr{sup +}=C(CH{sub 3}){sub 2}] = 39 {+-} 3 kcal/mol]. The observed reactivity requires unusual reaction mechanisms that are discussed in detail. 60 refs., 9 figs., 4 tabs.

• Sponsoring Organization: USDOE
• OSTI ID: 232273
• Journal Information: Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 6 Vol. 114; ISSN JACSAT; ISSN 0002-7863
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
ALKANES
CATIONS
CHEMICAL ACTIVATION
CHROMIUM
DEUTERIUM COMPOUNDS
GROUND STATES
ION-MOLECULE COLLISIONS
MASS SPECTROSCOPY
THERMODYNAMICS