UV Raman Spectrum of 1,3-Dimethylcyclopentenyl Cation Adsorbed in Zeolite H-MFI

Chua, Yek Tann; Stair, Peter C.; Nicholas, John B.; Song, Weiguo; Haw, James F.

doi:10.1021/ja028439+

Cited by 19 publications

(16 citation statements)

References 21 publications

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“…Only in a more recent and very elegant paper by the same group did they obtain the Raman signal of adsorbed 1,3-dimethylcyclopentenyl cation in H-MFI zeolite using the fluidized bed technique to minimize the 'coke' effect. 37 However, the spectra they obtained were apparently not SERS, but only normal surface Raman signals due to the significant increase in the surface adsorbed species in the zeolite similarly to that reported in Ref. 29.…”

Section: Uv-sers Of Pyridine On a Rh Electrodesupporting

confidence: 48%

Surface‐enhanced Raman spectroscopy with ultraviolet excitation

Lin

Ren

Yang

et al. 2005

J Raman Spectroscopy

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Surface-enhanced Raman scattering (SERS) spectroscopy excited with a UV laser was successfully developed and the UV-SER spectra of various adsorbates, including pyridine and SCN-, on different transition metal electrodes were obtained. The experimental requirements for obtaining UV-SERS in an electrochemical system are given. The surface enhancement factor of a roughened Rh electrode covered with thiocyanate as a model molecule was estimated to be about two orders of magnitude in the UV region, consistent with our preliminary theoretical calculation based on the electromagnetic model. The investigation of SERS in the UV region will improve the understanding of the SERS enhancement mechanism and broaden the research field of SERS in areas such as surface science and the life sciences. Copyright (c) 2005 John Wiley & Sons, Ltd

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Section: Uv-sers Of Pyridine On a Rh Electrodesupporting

confidence: 48%

Surface‐enhanced Raman spectroscopy with ultraviolet excitation

Lin

Ren

Yang

et al. 2005

J Raman Spectroscopy

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“…Chemie 13 C NMR [33] and low-resolution Raman spectroscopy. [34] Its structure combines carbocation-stabilizing features: fivemembered ring allyl resonance and optimally-placed methyl substituents. The intense C-C-C asymmetric allyl stretch at 1525 cm À1 is lower than the corresponding vibrations of the allyl cation (1581 cm À1 ) [35] or protonated benzene (1607 cm À1 ).…”

Section: Methodsmentioning

confidence: 99%

Structural Isomerization of the Gas‐Phase 2‐Norbornyl Cation Revealed with Infrared Spectroscopy and Computational Chemistry

et al. 2014

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In an attempt to produce the 2-norbornyl cation (2NB(+)) in the gas phase, protonation of norbornene was accomplished in a pulsed discharge ion source coupled with a supersonic molecular beam. The C7H11(+) cation was size-selected in a time-of-flight mass spectrometer and investigated with infrared laser photodissociation spectroscopy using the method of "tagging" with argon. The resulting vibrational spectrum, containing sharp bands in the C-H stretching and fingerprint regions, was compared to that predicted by computational chemistry. However, the measured spectrum did not match that of 2NB(+), prompting a detailed computational study of other possible isomers of C7H11(+). This study finds five isomers more stable than 2NB(+). The spectrum obtained corresponds to the 1,3-dimethylcyclopentenyl cation, the global minimum-energy structure for C7H11(+), which is produced through an unanticipated ring-opening rearrangement path.

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“…[34] Its structure combines carbocation-stabilizing features: fivemembered ring allyl resonance and optimally-placed methyl substituents. [34] Therefore, the assignment of the C 7 H 11 + ion in our experiment to DMCP + , the C 7 H 11 + global minimum, is unambiguous. [36] The prominent 2910 cm À1 absorption corresponds to the overlapping C À H stretches of the CH 3 and CH 2 groups.…”

mentioning

confidence: 99%

Structural Isomerization of the Gas‐Phase 2‐Norbornyl Cation Revealed with Infrared Spectroscopy and Computational Chemistry

et al. 2014

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In an attempt to produce the 2-norbornyl cation (2NB + ) in the gas phase, protonation of norbornene was accomplished in a pulsed discharge ion source coupled with a supersonic molecular beam. The C 7 H 11 + cation was sizeselected in a time-of-flight mass spectrometer and investigated with infrared laser photodissociation spectroscopy using the method of "tagging" with argon. The resulting vibrational spectrum, containing sharp bands in the CÀH stretching and fingerprint regions, was compared to that predicted by computational chemistry. However, the measured spectrum did not match that of 2NB + , prompting a detailed computational study of other possible isomers of C 7 H 11 + . This study finds five isomers more stable than 2NB + . The spectrum obtained corresponds to the 1,3-dimethylcyclopentenyl cation, the global minimum-energy structure for C 7 H 11 + , which is produced through an unanticipated ring-opening rearrangement path.The 2-norbornyl cation (C 7 H 11 + ; 2NB + ) is the most famous and controversial carbocation. [1,2] On the basis of unusual solvolysis reaction rates and products of 2-exo-and 2-endonorbornyl derivatives, [3][4][5][6][7][8] Winstein proposed a symmetrically bridged nonclassical structure for the ion intermediate. [5] In sharp disagreement, Brown favored rapidly equilibrating classical structures. [9] This dispute continued vehemently for decades. Experiments on 2NB + under "stable ion" conditions in "superacid" media supported the non-classical structure, as did theory at ever-more sophisticated levels. [10][11][12][13][14][15][16][17][18][19][20][21] Notably, Saunders demonstrated deuterium isotope effects on the 13 C NMR spectra showing no rapid equilibration, [14] and Yannonis cryogenic (5 K) 13 C NMR spectra showed a static symmetrically bridged structure. [15] However, proponents of the classical structure argued that these results were not definitive because of the long NMR time scale. Recently, the long-sought X-ray crystal structure of 2NB + was obtained, confirming its nonclassical structure in the condensed phase. [22] Nevertheless, questions remain about the nature of this ion in the gas phase. Is the isolated ion intrinsically stable, or is it stabilized by the counter ions and solvation in the superacid media? Although aspects of its chemistry have been studied by mass spectrometry, [23][24][25][26][27] no gas-phase spectroscopy of 2NB + has been reported. Our objective was to measure the infrared spectrum of the mass-selected C 7 H 11 + ion and to determine its structure from the vibrational patterns by comparison to the predictions of theory. To our surprise, the structure of C 7 H 11 + obtained under our conditions is not that of 2NB + , but instead corresponds to a much more stable rearranged ion. This rearrangement and the unexpected C 7 H 11 + isomer are the subjects of this paper. Previous mass spectrometry of 2NB + explored its reactions and collisional dissociation behavior. [23][24][25][26][27] Fragmentation patterns of C 7 H 11 + produced by different methods ...

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UV Raman Spectrum of 1,3-Dimethylcyclopentenyl Cation Adsorbed in Zeolite H-MFI

Cited by 19 publications

References 21 publications

Surface‐enhanced Raman spectroscopy with ultraviolet excitation

Surface‐enhanced Raman spectroscopy with ultraviolet excitation

Structural Isomerization of the Gas‐Phase 2‐Norbornyl Cation Revealed with Infrared Spectroscopy and Computational Chemistry

Structural Isomerization of the Gas‐Phase 2‐Norbornyl Cation Revealed with Infrared Spectroscopy and Computational Chemistry

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