Robert S. Sheridan

University of Nevada, Reno, Reno, Nevada, United States

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Publications (50)395.66 Total impact

  • Robert S. Sheridan
    ChemInform 11/2013; 44(45). DOI:10.1002/chin.201345228
  • Robert S Sheridan
    Chemical Reviews 06/2013; 113(9). DOI:10.1021/cr400150a · 45.66 Impact Factor
  • Myoung-Geun Song, Robert S Sheridan
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    ABSTRACT: Although aryl(trifluoromethyl)diazirines have achieved great popularity in photoaffinity labeling applications, the properties of the corresponding carbenes have not been as widely explored. Here, low-temperature matrix-isolation spectroscopy and reactivity studies indicate that in contrast to m-methoxyphenyl(trifluoromethyl)carbene and most known aryl(CF(3))carbenes, the para isomer is a ground-state singlet rather than triplet. DFT calculations support these results as well as the notion that the p-CH(3)O group stabilizes the singlet carbene via resonance. These results may have relevance to the wide range of substituted aryl(CF(3))diazirines in photoaffinity applications.
    Journal of the American Chemical Society 11/2011; 133(49):19688-90. DOI:10.1021/ja209613u · 11.44 Impact Factor
  • Myoung‐Geun Song, Robert S. Sheridan
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    ABSTRACT: B3LYP calculations indicate that substitution of a trifluoromethyl group for hydrogen stabilizes singlet versus triplet carbene states by a small, but systematic amount. Geometry and natural bond orbital analysis suggests that this energy lowering is due to rehybridization at the carbenic centers induced by the strong inductive electron-withdrawing effect of a CF3 group. The trifluoromethyl group also increases the electron affinity of the carbenes, consistent with the observed increased reactivity. Calculations also indicate that more strongly electron-withdrawing ammonium cationic ligands have an even more profound singlet stabilizing effect, suggesting a new type of ground-state singlet carbene. Copyright © 2011 John Wiley & Sons, Ltd.
    Journal of Physical Organic Chemistry 10/2011; 24(10):889 - 893. DOI:10.1002/poc.1913 · 1.23 Impact Factor
  • Robert S. Sheridan
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 07/2010; 41(30). DOI:10.1002/chin.201030278
  • [Show abstract] [Hide abstract]
    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 02/2010; 25(7). DOI:10.1002/chin.199407087
  • Robert S. Sheridan
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    ABSTRACT: Singlet carbenes exhibit very informative electronic spectra, which vary as a sensitive function of substituents and geometries. In particular, the lowest energy σ–p type excitations for singlet carbenes range broadly from the short wavelength UV to the near IR. Substituent effects on the energy of this key electronic transition can be rationalized by very simple orbital mixing arguments, and parallel similar influences on singlet–triplet energies. Besides providing valuable electronic information on singlet carbenes and bis-carbenes which have been studied by low temperature matrix isolation methods, UV/Vis spectroscopy has often guided investigations of conformation-dependent photochemistry of these species. Insights learned from experimental and calculated UV/visible spectra of a broad range of matrix isolated singlet carbenes and bis-carbenes are described. Copyright © 2010 John Wiley & Sons, Ltd.
    Journal of Physical Organic Chemistry 01/2010; 23(4):326 - 332. DOI:10.1002/poc.1649 · 1.23 Impact Factor
  • Jian Wang, Robert S Sheridan
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    ABSTRACT: Matrix-isolated 2-benzothienyl(trifluoromethyl)carbene was generated by irradiation of the corresponding diazirine, and characterized by IR and UV/vis spectroscopy, in situ trapping, and DFT modeling. Experiments and calculations indicate that the carbene is a ground-state singlet, in contrast to previously characterized aryl(trifluoromethyl)carbenes. The carbene could be interconverted photochemically with a ring-opened thioquinomethide and a highly strained cyclic allene.
    Organic Letters 09/2007; 9(16):3177-80. DOI:10.1021/ol071290s · 6.32 Impact Factor
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    ABSTRACT: [reaction: see text] Different conformers of two fused-ring cyclopropylchlorocarbenes are shown to undergo distinct, wavelength-selectable, photochemistry in low-temperature matrixes. Conformers with H and Cl syn give ring expansion predominantly, whereas those with H and Cl anti mainly fragment.
    Organic Letters 11/2006; 8(21):4963-6. DOI:10.1021/ol0620601 · 6.32 Impact Factor
  • Robert S. Sheridan
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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.
    Reviews of Reactive Intermediate Chemistry, 09/2006: pages 415 - 463; , ISBN: 9780470120828
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    ABSTRACT: [reaction: see text] Vinylchlorocarbenes (R = Me or Cl) cyclize to cyclopropenes with k = (2.4-5.1) x 10(7) s(-1) or (3.1-4.5) x 10(6) s(-1), respectively, in solution at room temperature. The corresponding E(a) values are 6.6 and 5.7 kcal/mol. Excited diazirines are also likely precursors of the cyclopropenes.
    Organic Letters 11/2005; 7(21):4645-8. DOI:10.1021/ol051743y · 6.32 Impact Factor
  • Asya F Nikitina, Robert S Sheridan
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    ABSTRACT: [reaction: see text] The highly strained cyclic allene 2,3-didehydro-2H-thiopyran was generated by irradiation of matrix-isolated 2-benzothienylchlorocarbene and characterized by IR and UV/vis spectroscopy, in situ trapping, and DFT modeling. Calculations indicate that the allenic moiety in this system, although less aromatic in character, is relatively more stable than in the corresponding oxa system. It is suggested that the thio ring system can more readily accommodate the allenic geometry.
    Organic Letters 10/2005; 7(20):4467-70. DOI:10.1021/ol051733x · 6.32 Impact Factor
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    ABSTRACT: Fused-ring cyclopropylchlorocarbenes 2 and 3 ring expand to fused-ring chlorocyclobutenes 10 and 11, respectively, with activation energies of 3–4 kcal/mol and activation entropies of ∼−20 e.u. Carbon tunneling appears to be unimportant at low temperatures.Graphical abstract
    Tetrahedron Letters 06/2005; 46(23):4137-4141. DOI:10.1016/j.tetlet.2005.03.209 · 2.39 Impact Factor
  • Peter S Zuev, Robert S Sheridan
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    ABSTRACT: The first direct spectroscopic characterization of singlet vinylcarbenes is reported. Several vinyl amidines were converted to the corresponding vinylchlorodiazirines through straightforward Graham oxidation. Irradiation of the diazirines at 8 K in N2 matrices gave the corresponding singlet vinylchlorocarbenes, which could be characterized by IR, UV/vis, and calculational modeling. Hence, vinylchlorocarbene, 1-methylvinylchlorocarbene, and 1-cyclopentenylchlorocarbene were all generated and investigated. The spectra are consistent with localized carbene structures compared to the very delocalized triplet vinylcarbenes. In all cases, the carbenes readily cyclize to the corresponding cyclopropenes on visible irradiation, together with H-shift in the parent vinylchlorocarbene. In the cyclopentenyl system, cyclization leads to a highly strained bicyclo[3.1.0]hexene.
    Journal of the American Chemical Society 11/2004; 126(39):12220-1. DOI:10.1021/ja046309q · 11.44 Impact Factor
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    ABSTRACT: Irradiation of 3-(3-noradamantyl)-3-chlorodiazirine produced the corresponding noradamantylchlorocarbene, which could be detected in solution with laser flash photolysis via its pyridinium ylide, and in N2 or Ar matrixes at 9 K with IR and UV/vis spectroscopy. At ambient temperatures, or on irradiation in the cryogenic matrixes, the carbene rearranged to 2-chloro-1-adamantene, which could be trapped in solution and which was characterized by IR and UV/vis at low temperatures. In the dark at 9 K, the carbene also slowly ring-expanded to the chloroadamantene, at a rate ca. 10111 times faster than predicted by its B3LYP-calculated activation barrier. It is proposed that the low-temperature rearrangement occurs through carbon quantum mechanical tunneling.
    Journal of the American Chemical Society 09/2004; 126(33):10196-7. DOI:10.1021/ja0488939 · 11.44 Impact Factor
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    ABSTRACT: We observed ring expansion of 1-methylcyclobutylfluorocarbene at 8 kelvin, a reaction that involves carbon tunneling. The measured rate constants were 4.0 x 10(-6) per second in nitrogen and 4 x 10(-5) per second in argon. Calculations indicated that at this temperature the reaction proceeds from a single quantum state of the reactant so that the computed rate constant has achieved a temperature-independent limit. According to calculations, the tunneling contribution to the rate is 152 orders of magnitude greater than the contribution from passage over the barrier. We discuss environmental effects of the solid-state inert-gas matrix on the reaction rate.
    Science 03/2003; 299(5608):867-70. DOI:10.1126/science.1079294 · 31.48 Impact Factor
  • Asya Nikitina, Robert S Sheridan
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    ABSTRACT: Irradiation of N(2) matrix-isolated 3-chloro-3-(2-benzoxazolyl)diazirine gives a mixture of syn- and anti-benzoxazolylchlorocarbenes which could be characterized by IR, UV/vis, and B3LYP modeling. Subsequent irradiation of the carbene caused ring opening to the corresponding quinoimine, which was similarly characterized. In turn, the quinoimine photochemically underwent ring-closure to a novel, highly strained cyclic ketenimine. Unrestricted singlet DFT calculations were required to fit the IR spectrum of the ketenimine, suggesting significant diradical character. Photolysis of the ketenimine led to ring cleavage in yet another fashion, to give an isonitrile-phenoxychlorocarbene, whose spectra were similar to those of the previously characterized phenoxychlorocarbene. Finally, at shorter wavelengths, the phenoxycarbene underwent the expected rearrangement to the corresponding benzoyl chloride.
    Journal of the American Chemical Society 08/2002; 124(26):7670-1. DOI:10.1021/ja026300t · 11.44 Impact Factor
  • Brian F. LeBlanc, Robert S. Sheridan
    Journal of the American Chemical Society 04/2002; 110(21). DOI:10.1021/ja00229a070 · 11.44 Impact Factor
  • Peter S. Zuev, Robert S. Sheridan
    Journal of the American Chemical Society 04/2002; 116(20). DOI:10.1021/ja00099a086 · 11.44 Impact Factor
  • Peter Zuev, Robert S. Sheridan
    [Show abstract] [Hide abstract]
    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 04/2002; 116(9). DOI:10.1021/ja00088a076

Publication Stats

657 Citations
395.66 Total Impact Points

Institutions

  • 1988–2013
    • University of Nevada, Reno
      • Department of Chemistry
      Reno, Nevada, United States
  • 2004–2005
    • Rutgers, The State University of New Jersey
      • Department of Chemical Biology
      New Brunswick, NJ, United States
  • 2002
    • University of Wisconsin–Madison
      • Department of Chemistry
      Madison, Wisconsin, United States
    • University of Rochester
      • Department of Chemistry
      Rochester, New York, United States