Department of Chemistry

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End date: 2009Subject: search.filters.subject.Hydrocarbons

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Now showing 1 - 8 of 8
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    Protonated Benzene Dimer: An Experimental and Ab Initio Study
    (ACS, 2009-07-21) Chakraborty, Shamik
    The excitation spectrum of the protonated benzene dimer has been recorded in the 415−600 nm wavelength range. In contrast to the neutral iso-electronic benzene dimer, its absorption spectrum extends in the visible spectral region. This huge spectral shift has been interpreted with ab initio calculations, which indicate that the first excited states should be charge transfer states.
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    Cyclization of Oxa-Bicyclic Alkenes with β-Iodo-(Z)-propenoates and o-Iodobenzoate Catalyzed by Nickel Complexes:  A Simple Efficient Route to Annulated Coumarins
    (ACS, 2003) Shukla, Paritosh
    In the presence of Ni(dppe)Br2 and Zn powder in acetonitrile at 80 °C, oxa-bicyclic olefins undergo cyclization with o-iodobenzoate and with β-iodo-(Z)-propenoates to give the benzocoumarin derivatives in moderate to good yields. This methodology offers a simple efficient way for the synthesis of structurally complicate coumarins in one pot.
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    Facile β-Alkyl and β-Hydride Elimination in the Nickel-Catalyzed Annulation of o-Iodophenyl Ketones and Aldehydes with Bicyclic Alkenes
    (ACS, 2006-05-26) Shukla, Paritosh
    o-Iodoaryl aldehydes react with bicyclic alkenes in the presence of NiBr2(dppe) and Zn powder in acetonitrile at 80 °C undergoing annulation to give polycyclic ketone derivatives. Surprisingly, o-iodoaryl alkyl ketones also react with bicyclic alkenes to form polycyclic ketones with structures the same as those from the corresponding o-iodoaryl aldehydes.
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    Diazapentacene Derivatives as Thin-Film Transistor Materials: Morphology Control in Realizing High-Field-Effect Mobility
    (ACS, 2009) Shukla, Paritosh
    5,7,12,14-Tetrachloro-6,13-diaza-6,13-dihydropentacene (TCDAHP) and 5,7,12,14-tetrachloro-6,13-diazapentacene (TCDAP) were synthesized and assessed as the active channel materials for thin-film transistor applications. Analyses of the crystal structures of these molecules revealed that both exhibited slipped π−π stacking of the long and fused aromatic moiety. Although the packing features of the two compounds are basically identical, their highest occupied molecular orbitals, which are relevant to hole transport, are very different. Better mobility was predicted for TCDAHP over TCDAP based on the dimeric structure in the X-ray coordinates. The morphologies of thin films of TCDAHP and TCDAP prepared by thermal evaporation depend critically on the substrate on which the molecules were deposited: from the amorphous state on a SiO2/Si surface to the crystalline state on a pentacene buffer layer surface. The performance of thin-film transistors prepared on various substrate surfaces was studied. While no field-effect mobility was observed for these films deposited on SiO2/Si, a high mobility of 1.4 cm2/(V s) for the TCDAHP film was achieved when deposited on a pentacene buffer layer prepared on a rubbed monolayer of n-nonyltrichlorosilane on a SiO2/Si surface. A similar device prepared from TCDAP gave a mobility of 0.13 cm2/(V s).
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    Microwave-Accelerated Solvent-Free Synthesis of Thioketones, Thiolactones, Thioamides, Thionoesters, and Thioflavonoids
    (RSC, 1999-07-29) Kumar, Dalip
    An expeditious, solvent-free, and high yield conversion of ketones, flavones, isoflavones, lactones, amides, and esters to the corresponding thio analogues is described utilizing Lawesson's reagent in a process that circumvents the use of dry solvents and excess of the reagent.
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    Synthesis and Thermolysis of Heterocyclic 3-Aza-3-ene-1,5-diynes
    (ACS, 2002-11-12) Kumar, Dalip
    Simple, acyclic 3-aza-3-ene-1,5-diynes undergo an aza-Bergman rearrangement to a fleeting 2,5-didehydropyridine (2,5-ddp) intermediate that rapidly ring-opens to β-alkynylacrylonitrile products. In an effort to access longer-lived 2,5-ddp intermediates, we have prepared heterocyclic 3-aza-3-ene-1,5-diynes. The thermolysis of one such heterocyclic aza-enediyne does not afford products derived from trapping a 2,5-ddp intermediate but rather cyclopropanes that appear to arise from a carbene intermediate and a product that appears to be a trapping product from a 2,3-ddp intermediate.
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    An Extremely Facile Aza-Bergman Rearrangement of Sterically Unencumbered Acyclic 3-Aza-3-ene-1,5-diynes
    (ACS, 2003-02) Kumar, Dalip
    The factors that affect the kinetics of the aza-Bergman cyclization of aza-enediynes (C,N-dialkynyl imines) have not previously been elucidated. Here we report our kinetic studies of the aza-Bergman reactions of a series of 6-triisopropylsilyl and 6-unsubstituted 1-phenyl-4-aryl-3-aza-3-ene-1,4-diynes in which the aryl group is phenyl, o-(methoxy)phenyl, or p-(methoxy)phenyl. These aza-enediynes are prepared as single isomers in modest yield from the corresponding 1-aryl-3-(triisopropylsilyl)propynone oximes. These aza-enediynes undergo aza-Bergman reaction followed by a rapid retro-aza-Bergman cyclization to afford β-alkynyl acrylonitrile products. In no case are products corresponding to trapping the intermediate 2,5-didehydropyridine diradical isolated. While the rate of aza-Bergman cyclization is not greatly affected by the nature of the 4-aryl substituent, the rate is very dependent on the nature of the 6-substituent. 1-Phenyl-4-aryl-3-aza-3-ene-1,5-diynes that lack a 6-substituent undergo aza-Bergman cyclization spontaneously at 20 °C with first-order half-lives of 36−78 min. The effect of solvent on the kinetics of aza-Bergman cyclization of 1,4-diphenyl-3-aza-3-ene-1,5-diyne was investigated. The rate of this cyclization is solvent dependent, proceeding more rapidly in less polar solvents.
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    Anchored Pd Complex in MCM-41 and MCM-48:  Novel Heterogeneous Catalysts for Hydrocarboxylation of Aryl Olefins and Alcohols
    (ACS, 2002) Sarkar, Bibhas R.
    We report here, for the first time, synthesis of anchored Pd complexes in mesoporous supports such as MCM-41 and MCM-48 as true heterogeneous catalysts for hydrocarboxylation of aryl olefins and alcohols to give excellent conversion (∼100%) and regioselectivity (∼99%) for 2-arylpropionic acids. The catalysts were characterized by powder-XRD, 31P CP-MAS NMR, FT-IR, TEM, XPS and ICP-AES. Recycle studies with these anchored Pd mesoporous catalysts were performed to confirm true heterogeneity.