Spectroscopy of C-H stretching vibrations of gas-phase butenes: cis-2-butene, trans-2-butene, 2-methyl-2-butene, and 2,3-dimethyl-2-butene

Manzanares, Ignacio; Blunt, Victor M.; Peng, Jianbing

doi:10.1021/j100118a013

Cited by 14 publications

(8 citation statements)

References 8 publications

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“…Four absorption bands dominate both spectra: the asymmetric methyl deformation (δ as (CH 3 ) at 1450 cm -1 ), the CdC stretching (ν(CdC) at 1605 cm -1 ), and the symmetric and asymmetric C-H stretching of the terminal methyl groups (ν s (CH 3 ) and ν as (CH 3 ) at 2860 and 2915 cm -1 , respectively). [100][101][102][103] The presence of the carbon-carbon double bond vibration at 1605 cm -1 in particular attests to the previous conclusion concerning the molecular nature of cis-2-butene adsorption on the oxide surface. In fact, adsorption of butene may be relatively weak, since the CdC double bond does not undergo the strong sp 3 rehybridization due to formation of a di-σ bonded complex typically seen for alkenes on metal surfaces.…”

Section: Resultssupporting

confidence: 63%

“…Guo and Madix 16 ascribed the absence of hydrogenation of the various alkenes they studied on Pd (100) to the strong hydrogen adsorption on that surface. Similarly, the weakening of metal-hydrogen bonds in the presence of coadsorbates was invoked to explain the promotion of alkene hydrogenation on both a Ni-precovered Pt(111) surface [28][29][30] and on a Fe (100) surface predosed with CO. 31,32 Zaera has suggested that the first half-hydrogenation to alkyl species may be the rate-limiting step in alkene hydrogenation, and that the β-hydride elimination then competes favorably against the reductive elimination step with coadsorbed hydrogen that leads to alkane production. 33,34 More recently, the thermal chemistry of alkenes has been studied in our group on more realistic model catalysts consisting of Pd nanoparticles supported on Al 2 O 3 /NiAl(110) oxide films.…”

Section: Introductionmentioning

confidence: 99%

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Isomerization and Hydrogenation ofcis-2-Butene on Pd Model Catalyst

et al. 2008

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The adsorption and kinetics of conversion of cis-2-butene with deuterium on model supported Pd catalyst (Pd/Fe 3 O 4 /Pt(111)) were characterized by reflection-absorption infrared spectroscopy (RAIRS), temperatureprogrammed desorption (TPD), and isothermal molecular beam (MB) experiments. It was found that selectivity toward cis-trans isomerization and hydrogenation depends critically on the nature of the carbonaceous deposits, which are typically present during reaction on real catalysts. At low temperatures (190-210 K) both reaction pathways were found to proceed on the initially clean surface, but the catalytic activity was observed to quickly vanish, presumably because of the accumulation of hydrocarbon species on the surface. At temperatures above 250 K, on the other hand, a sustained catalytic activity toward cis-trans isomerization was observed over long periods of time. Interestingly, no catalytic activity could be sustained for the competing hydrogenation on the initially clean catalyst even at these temperatures. Only when highly dehydrogenated carbonaceous fragments were preadsorbed on the surface was it possible to induce a persistent catalytic activity for the hydrogenation (and also the isomerization) of the alkene on our supported palladium particles. Possible reasons of this unique vacuum catalytic behavior are discussed, including different spatial requirements for the competing reaction pathways and changes in the adsorption state of deuterium on and beneath the surface modified by the carbonaceous deposits.

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Section: Resultssupporting

confidence: 63%

Section: Introductionmentioning

confidence: 99%

Isomerization and Hydrogenation ofcis-2-Butene on Pd Model Catalyst

et al. 2008

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“…The feature observed at 872 cm -1 is assigned to ν 16 , the C−C in plane stretch between the methyl group and the first allyl carbon. The observed frequency is in good agreement with similar frequencies observed for the H 3 C−C stretch in the 2-methylallyl radical (865 cm -1 ), cis −2-butene (870 cm -1 ), trans -2-butene (863 cm -1 ), eclipsed 1-butene (836 cm -1 ), and gauche 1-butene (854 cm -1 ) …”

Section: Discussionsupporting

confidence: 86%

“…The vibrational frequencies for the 1-methylallyl radical correlate with experimental values obtained for the allyl radical, , the 2-methylallyl radical, methyl formate, and propenal . The vibrational frequencies are compared with the eclipsed and gauche conformations of 1-butene, trans -1,3-butadiene, and the two isomeric forms of butene in Table 1 Vibrational Assignments for the 1-Methylallyl Radical assignmentab-initio 6-31G* (90% corr)1-methylallyl radical, this work2-methylallyl radical a allyl radical b methyl formate c propenal c A‘ ν 1 CH 2 asym stretch 3092 3107 3103 ν 2 CH asym stretch 3015 3028 ν 3 CH 2 sym stretch 3013 3051 3000 ν 4 CH sym stretch 3003 2943 2800 ν 5 CH 3 asym stretch 2949 3045 ν 6 CH 3 sym stretch 2873 2969ν 7 CH 3 deform (asym) 1482 1454 ν 8 CH 2 scissor (sym) 1478 1492 1492 1488 1420 ν 9 CH asym bend 1449 ν 10 CH 3 deform (sym) 1403 1392 1445 ν 11 CH ip sym, bend 1305 1265 1275 ν 12 CCC asym stretch 1219 1184 ν 13 CCC sym stretch 1132 1037 1066 ν 14 CH 3 -C−C asym str 1077 ν 15 CH 2 ,CH 3 rock (sym) 960 912 …”

Section: Resultsmentioning

confidence: 78%

“…The C−H in plane bend of propenal (1275 cm -1 , C s point group) was used to assign the mode because the molecule has similar force constants and reduced mass as the 1-methylallyl radical (1265 cm -1 ) . The frequencies observed for the CH bend in eclipsed 1-butene (1306 cm -1 ), gauche 1-butene (1296 cm -1 ), cis -2-butene (1260 cm -1 ), trans -2-butene (1306 cm -1 ), and trans -1,3-butadiene (1280 cm -1 ) 31 are consistent with the C−H bending frequency observed for the 1-methylallyl radical.…”

Section: Discussionmentioning

confidence: 99%

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Resonance Raman Spectroscopy of the 1-Methylallyl Radical

et al. 1996

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The first vibrational spectrum of the 1-methylallyl radical is detected using resonance Raman spectroscopy with excitation from 237 to 232 nm. The vibrational frequencies of five symmetric fundamentals, the H 3 C-CCC bend, the CCC bend, the H 3 C-C stretch, the C-H in plane bend, and the CH 2 scissors, of the 1-methylallyl radical are reported. The even overtones of the CH 3 torsion, the C-H out of plane bend, the H 3 C-CCC bend, and the CCC bend are identified. The vibrational assignments of the resonance Raman spectra are based upon comparison with calculated vibrational frequencies generated by UHF method using a 6-31G* basis set and experimental values for the allyl radical, the β-methylallyl radical, and similar molecules. Excitation at 236.05 and 234.95 nm yields significant resonance enhancement of overtone and combination bands associated with the H 3 C-CCC bend and CCC bend, respectively. The variation of intensities in the Raman spectra with excitation wavelength yields excited state vibrational frequencies for the H 3 C-CCC bend and CCC symmetric bend of 305 and 502 cm -1 , respectively. Examination of the observed intensity patterns in the resonance Raman spectra indicates that the initial excited state dynamics of the 1-methylallyl radical are dominated by bending motions of the carbon chain.

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