Electrochemical unzipping of multi-walled carbon nanotubes for facile synthesis of high-quality graphene nanoribbons

Here we report a remarkable transformation of carbon nanotubes (CNTs) to nanoribbons composed of a few layers of graphene by a two-step electrochemical approach. This consists of the oxidation of CNTs at controlled potential, followed by reduction to form graphene nanoribbons (GNRs) having smooth edges and fewer defects, as evidenced by multiple characterization techniques, including Raman spectroscopy, atomic force microscopy, and transmission electron microscopy. This type of "unzipping" of CNTs (single-walled, multi-walled) in the presence of an interfacial electric field provides unique advantages with respect to the orientation of CNTs, which might make possible the production of GNRs with controlled widths and fewer defects.     

Kinetics of perborate oxidation of quinol

The perborate oxidation of quinol in aqueous acetic acid is first order with respect to perborate, zero order with respect to quinol, and first order with respect to H⁺. The oxidation is faster than H₂O₂ oxidation. Breakdown of protonated perboric acid is suggested as the rate-limiting step.

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Characterization of covalent linkages in organically functionalized MCM-41 mesoporous materials by solid-state NMR and theoretical calculations

The covalent linkages formed during functionalization of MCM-41 mesoporous molecular sieves with five chloroalkylsilanes ((EtO)3Si(CH2Cl), (MeO)3Si(CH2CH2CH2Cl), Cl3Si(CH2CH2CH3), Cl2Si(CH3)(CH2Cl) and Cl2Si(CH3)2) have been investigated using high-resolution solid-state NMR spectroscopy and DFT calculations. Structural information was obtained from 1H-13C and 1H-29Si heteronuclear (HETCOR) NMR spectra, in which high resolution in the 1H dimension was obtained by using fast MAS. The 1H-13C HETCOR results provided the assignments of 1H and 13C resonances associated with the surface functional groups. Sensitivity-enhanced 1H-29Si HETCOR spectra, acquired using Carr-Purcell-Meiboom-Gill refocusing during data acquisition, revealed the identity of 29Si sites (Qn, Tn, and Dn) and the location of functional groups relative to these sites. Optimal geometries of local environments representing the Qn, Tn and Dn resonances were calculated using molecular mechanics and ab initio methods. Subsequently, DFT calculations of 29Si, 13C, and 1H chemical shifts were performed using Gaussian 03 at the B3LYP/6-311++G(2d,2p) level. The theoretical calculations are in excellent accord with the experimental chemical shifts. This work illustrates that state-of-the-art spectroscopic and theoretical tools can be used jointly to refine the complex structures of inorganic-organic hybrid materials.     

Conformational and configurational studies on 3-azabicyclo[3.3.1]nonane (3-abn) derivatives and related systems employing carbon-13 NMR spectroscopy

The ¹³C nmr spectra of 4 cis-2,4-diphenyl-3-azabicyclo[3.3.1]nonanes, 11 cis-2,4-diaryl-3-azabicyclo[3.3.1]-nonan-9-ones, 26 cis-2,4-diaryl-3-azabicyclo[3.3.1]-nonan-9-ols or acetates thereof, 5 cis-2,4-diaryl-3-azabi-cyclo[4.3.1]decan-10-ones or -10-ols and 5 cis-2,4-diphenyl-3-aza-7-thiabicyclo[3.3.1]nonan-9-ones, -9-ols or 9-yl acetates have been recorded. Except for the 7-thia compounds, which appear to exist mainly in the configuration and conformation with the nitrogen-containing ring in the boat form, these compounds seem to exist overwhelmingly in chair-chair conformations. The configuration of the 9-ols and their acetates (syn or anti to the nitrogen-containing ring) has been deduced from the spectra. In a number of cases, the structures assigned differ from those earlier postulated. Broadening of one set of aryl signals (probably those due to the ortho carbons) in the case of N-methyl (but not N-H) compounds without ortho substituents is ascribed to restricted phenyl rotation.     

New methods for obtaining the matrix of direction cosines in three-dimensional structures

In this work four new methods of obtaining the matrix of direction cosines, which are needed in the static or dynamic analysis of three-dimensional structures, are discussed. Their applications in two different fields are illustrated by suitable examples.     

Kinetics of oxidation of some meta- and para-substituted phenyl methyl sulfoxides by chloramine-T in buffered ethanol–water

The kinetics of oxidation of methyl phenyl sulfoxide by chloramine-T (CAT) has been studied in buffered ethanol–water (1:1 v/v) of pH 7.0. The reaction was found to follow no simple-order kinetics. A possible mechanism is suggested involving three rate-controlling steps: (1) the reaction between RNHCl (R = CH₃C₆H₄SO₂) and the sulfoxide, (2) the disproportionation of RNHCl, and (3) the reaction between RNCl₂ and the sulfoxide. A mixed-order rate law is derived as rate/[C][SO] = k₁ + K_dk₂[C]/[SA]. The rate law is found to be obeyed for the meta- and para-substituted phenyl methyl sulfoxides also. The ρ value is obtained using Hammett's σ constants. The ρ values obtained for the attack of both RNHCl and RNCl₂ with the sulfoxides are almost the same, showing that both are converting the sulfoxide to the same intermediate. A chlorinium ion transfer is suggested.     

Triple-quantum magic angle spinning (27)Al NMR of aluminum hydroxides

We show that (27)Al triple-quantum magic angle spinning (3Q-MAS) experiments alleviate the second-order quadrupolar broadening to reveal the structure-building units of nonequivalent aluminum octahedra in the most extensively studied aluminum hydroxides, namely, gibbsite, bayerite, and boehmite. Further, aided by ab initio calculations of the electric field gradient tensors, the 3Q-MAS/MAS results are shown to lead to the assignment of (27)Al isotropic resonances to the aluminum positions in their X-ray-determined structures. The present work paves the way for future studies on various structurally transformed materials derived from these basic aluminum hydroxides.     

A formal convergent synthesis of (+)-trans-solamin

A formal convergent synthesis of solamin is disclosed. The synthetic strategy exploits the potential of the sulfinyl group as an auxiliary, nucleophile and in C-C bond formation. The synthetic route can be adapted to the synthesis of stereoisomers of solamin, analogs with variable carbon side chains, and other members of mono-THF acetogenins.     

Highly Efficient Direct Synthesis of Scaffold 9a,10,12,12a‐Tetrahydrobenzo[b]cyclopenta[f]pyrrolo[1,2‐d][1,4]diazepinone by Using Active Phoshomolybdic Acid

Domino coupling of furan‐2‐yl (phenyl) methanol and 2‐(1H‐pyrrol‐1‐yl) aniline has been achieved in the presence of 10 mol% phosphomolybdic acid in CH₃CN under reflux to afford the corresponding biologically active 10‐aryl‐9a,10,12,12a‐tetrahydrobenzo[b]cyclopenta[f]pyrrolo[1,2‐d][1,4]diazepin‐11(9H)‐ones in good yields. Broad substrate scope, short reaction times, environmentally benign, and operational simplicity makes this method more attractive.     

Enantioselective Total Synthesis of Chromanone Lactone Homo‐ and Heterodimers

A one pot borylation/Suzuki–Miyaura reaction of the 4‐bromochromanone lactones 21 and 23 , respectively, followed by cleavage of the methyl ether moieties gave the homodimeric chromanone lactones 10 and 11 . Reaction of a 1:1 mixture of 21 and 23 under otherwise identical conditions gave a 1:1:2‐mixture of the two homodimers 10 and 11 and the heterodimer 12 . This is the first example of the preparation of a heterodimeric chromanone lactone. For the enantioselective synthesis of the starting material, phenol 17 was transformed into the chromane 18 using a Wacker‐type cyclisation with 99 % ee and 80 % yield.