Ravi Pratap Singh

An efficient method for aromatic Friedel–Crafts alkylation, acylation, benzoylation, and sulfonylation reactions

Abstract Aromatic electrophilic substitution reactions such as alkylation, acylation, benzoylation, and sulfonylation were studied in the presence of a catalytic amount of Cu(OTf) 2 and Sn(OTf) 2 . Cu(OTf) 2 was very efficient for alkylation, acylation, and benzoylation reactions. However, in case of sulfonylation reactions, Sn(OTf) 2 gave better results.

Colliding plasma plume dynamics and ZnO thin film deposition

Dynamics of single and two collinearly colliding laser ablated plumes studied using fast imaging and the spectroscopic measurement is reported. The two expanding plumes colliding with each other resulting in the formation of a stagnation layer at the interface region which depend on mean free path and distance between the two plumes. The overlapping region lasts for several microseconds with significant concentration of nanoparticles/ cluster in gaseous phase. The dynamical growth of ZnO nanoparticles is ascertained using Rayleigh scattered second harmonic radiation at 532 nm of Nd:YAG laser. Intensity variation in the Rayleigh scattered signal and blue shift in photoluminescence peak position at different temporal delays with respect to the ablation pulse corroborates the presence and size variation of nano-particles/clusters formed in the vapor phase of ablated ZnO. The thin films of ZnO deposited on glass (polycrystalline) substrate are observed to have preference for single orientation. The presence of low ionic species in the overlap region seems to play a role in getting singly oriented thin films.

DBU-Mediated Diastereoselective Aldol-Type Cyanomethylation of Isatins

An efficient, metal-free approach to 3-substituted 3-hydroxyoxindole by DBU-mediated highly diastereoselective addition of aryl acetonitrile to N-protected isatin under mild conditions has been developed. The reaction proceeds smoothly to produce respective cyanomethylated adducts in good yield and excellent diastereoselectivity. Further transformation of the cyanide group allowed the synthesis of an advance intermediate of corresponding (±) CPC analogue. The mechanistic insight toward the aldol-type cyanomethylation of N-tritylisatin with benzyl cyanide was obtained by DFT calculations.

Intramolecular Dehydrogenative Coupling of 2,3-Diaryl Acrylic Compounds: Access to Substituted Phenanthrenes

A simple, facile, and environmentally benign intramolecular dehydrogenative coupling of various 1,2-diarylethylenes for the synthesis of phenanthrenes in excellent yield has been described. This new methodology uses ceric ammonium nitrate (CAN) as a promoter at room temperature and has been extended to intermolecular synthesis of biaryl compounds. The electron transfer from methoxyarene to cerium leads to cationic radical formation, which further proceeds to intramolecular coupling. Preliminary mechanistic investigation by EPR spectroscopy and density functional theory calculation suggested a similar view.

Optical probe investigation of laser ablated carbon plasma plume in nitrogen ambient

We report the study of carbon plasma produced using 1064u2009nm laser in nitrogen ambient at atmospheric pressure using 2-dimensional fast imaging of ablated plume, optical emission spectroscopy, and optical probe at 532u2009nm for interferometry and shadowgraphy. The dominance of C2 and CN molecules over ionic species at later stages of expanding carbon plasma plume is reported. The observed ring structure in shadowgrams and change in the direction of fringe shift from positive to negative in recorded interferograms are correlated with the relative abundance of different species in the plasma plume as function of time delay with respect to ablating pulse. An agreement in observed onset time of formation of clusters/atomic species or low ionic species using different diagnostic techniques has been reported.

Time resolved diagnostics of ions in colliding carbon plasmas

We report a comparative study of the dynamic behaviour of ions at different pressures in laser ablated colliding and single plasma plumes using 2D imaging, optical emission spectroscopy (OES) and a retarding field analyser (RFA). 2D imaging shows the splitting of plasma plumes due to different velocities of various plasma species. OES shows enhancement in abundance of ionic species with their presence for a longer time in colliding plume. C2 molecular formation is seen at later time in colliding plume compared to single plume and is attributed to dominating collisional processes in the colliding region of the plumes. The time of flight distribution of ions traced by the RFA shows the variation with change in fluence as well as ambient pressure for both colliding and single plume. Time of flight analysis of ions also shows the appearance of a fast peak in ion signal due to acceleration of ions at larger fluence.

Vibrational properties of NiPd and NiCr alloys

The augmented space cluster coherent potential approximation is applied to the study of the vibrational properties of NiPd and NiCr alloys. Together with the earlier work on NiPt, this forms a systematic study of effects of large mass and force-constant disorders and clustering effects. The AS-CCPA represents a significant improvement over the earlier MCPA calculations in comparison with experimental data.

Third harmonic generation in air ambient and laser ablated carbon plasma

We report the third harmonic generation of a nanosecond laser pulse (1.06u2009μm) in air ambient and in the presence of nanoparticles from laser ablated carbon plasma. Significant decrease in the threshold of third harmonic generation and multi-fold increment in the intensity of generated third harmonic is observed in presence of carbon plasma. The third harmonic in air is due to the quasi-resonant four photon process involving vibrationally excited states of molecular ion of nitrogen due to electron impact ionization and laser pulse. Following optical emission spectroscopic observations we conclude that the presence of C2 and CN in the ablated plume play a vital role in the observed third harmonic signals.

Time resolved optical diagnostics of ZnO plasma plumes in air

We report dynamical evolution of laser ablated ZnO plasma plumes using interferometry and shadowgraphy; 2-D fast imaging and optical emission spectroscopy in air ambient at atmospheric pressure. Recorded interferograms using Nomarski interferometer and shadowgram images at various time delays show the presence of electrons and neutrals in the ablated plumes. The inference drawn from sign change of fringe shifts is consistent with two dimensional images of the plume and optical emission spectra at varying time delays with respect to ablating pulse. Zinc oxide plasma plumes are created by focusing 1.06 μm radiation on to ZnO target in air and 532u2009nm is used as probe beam.