Comparison of experimental and ab initio HF and DFT vibrational spectra of benzimidazole

In this work, we will report a combined experimental and theoretical study on molecular and vibrational structure of benzimidazole. The laser Raman and Fourier transform infrared spectra of benzimidazole were recorded in the solid phase. The equilibrium geometry, harmonic vibrational frequencies, infrared intensities, Raman scattering activities, depolarization ratios and reduced masses were calculated by HF and density functional B3LYP method with the 6-311G(d,p) basis set. The scaled theoretical wavenumbers showed very good agreement with the experimental values. The thermodynamic functions of the title compound were also performed at HF/6-31G(d,p)/6-311G(d,p) and B3LYP/6-31G(d,p)/6-311G(d,p) levels of theory. A detailed interpretations of the infrared and Raman spectra of benzimidazole is reported. The theoretical spectrograms for FT-IR spectra of the title molecule have been constructed.     

Cyanuric chloride catalyzed metal-free mild protocol for the synthesis of highly functionalized tetrahydropyridines

An environmentally benign, facile and elegant synthetic approach for the convenient access of a series of diverse 2,6-diaryl-tetrahydropyridine-3-carboxylates via a one-pot, pseudo five-component condensation of ethyl acetoacetate, anilines and aromatic aldehydes under mild reaction conditions has been described. This domino strategy allows rapid cyclization in the presence of 10 mol% of cyanuric chloride as a source of hydrochloric acid to afford the desired target skeletons in excellent yields. The present protocol offers prominent advantages of simple operational procedure, metal-free organocatalyst, practically robust and extensive substrate scope.     

Reversal of Regioselectivity in Asymmetric C−H Bond Annulation with Bromoalkynes under Cobalt Catalysis**

Metal-catalyzed asymmetric C−H bond annulation strategy offers a versatile platform, allowing the construction of complex P-chiral molecules through atom- and step-economical fashion. However, regioselective insertion of π-coupling partner between M−C bond with high enantio-induction remain elusive. Using commercially available Co(II) salt and chiral-Salox ligands, we demonstrate an unusual protocol for the regio-reversal, enantioselective C−H bond annulation of phosphinamide with bromoalkyne through desymmetrization. The reaction proceeds through ligand-assisted enantiodetermining cyclocobaltation followed by regioselective insertion of bromoalkyne between Co−C, subsequent reductive elimination, and halogen exchange with carboxylate resulted in P-stereogenic compounds in excellent ee (up to >99 %). The isolation of cobaltacycle involved in the catalytic cycle and the outcome of control experiments provide support for a plausible mechanism.     

Adsorption of H2 molecules on B/N-doped defected graphene sheets—a DFT study

Structural Chemistry - Adsorption of hydrogen molecules on the surface of two-dimensional sheets is extremely challenging due to the non-polar nature of the molecules. Though the adsorption occurs...     

Drug encapsulation within self-assembled microglobules formed by thermoresponsive supramolecules

An 8-(phenyl)-2'-deoxyguanosine derivative self-assembles in aqueous media into discrete hexadecamers that further self-assemble above 32 °C into microglobules that encapsulate the drug doxorubicin.     

Non-Wieferich primes in number fields and <Emphasis Type="Italic">abc</Emphasis>-conjecture

Let K/Q be an algebraic number field of class number one and let O _K be its ring of integers. We show that there are infinitely many non-Wieferich primes with respect to certain units in O _K under the assumption of the abc-conjecture for number fields.     

Space-time tradeoffs in negative cycle detection - An empirical analysis of the Stressing Algorithm

This paper discusses space-time tradeoffs associated with algorithms for the problem of detecting negative cost cycles in networks (NCCD). NCCD is one of the more ubiquitous problems in computer science and operations research, with applications ranging from program verification and real-time scheduling to image segmentation and shortest path identification. Typical algorithmic analysis, whether theoretical or empirical, focuses almost exclusively on the running time of the algorithm. However, there exist applications in which space is just as important a parameter as time is. This is especially true when the problem instances are very large, as is the case in program verification. Consequently, an algorithm that minimizes running time while ignoring the space overhead may be impractical. In this paper, we analyze a number of the more common algorithms for NCCD from the perspectives of both time and space, with a view towards providing a space-time tradeoff for the practitioner. All the algorithms discussed in this paper (with the exception of Network Simplex) run in O(m·n) time on a network with m arcs and n vertices; however, their space requirements range from O(1) (Stressing Algorithm) to Ω(n) (all the Bellman-Ford and Network Simplex variants). Our empirical results demonstrate that in the cases where space is paramount, the Stressing Algorithm is a useful alternative to the Bellman-Ford variants.     

Chiral Phosphoric Acid Catalyzed Kinetic Resolution of 2-Amido Benzyl Alcohols: Asymmetric Synthesis of 4H-3,1-Benzoxazines

An efficient method for the asymmetric synthesis of 4H-3,1-benzoxazines was developed by kinetic resolution of 2-amido benzyl alcohols using chiral phosphoric acid catalyzed intramolecular cyclizations. A broad range of benzyl alcohols (both secondary and tertiary alcohols) were kinetically resolved with high selectivities, with an s factor of up to 94. Mechanistic studies were performed to elucidate the mechanism of these reactions, wherein the amide moieties reacted as the electrophiles. Gram-scale reaction and facile transformations of the chiral products demonstrate the potential of this method in asymmetric synthesis of biologically active chiral heterocycles.     

Regioselective and Enantioselective Synthesis of β‐Indolyl Cyclopentenamides by Chiral Anion Catalysis

The regioselective and enantioselective synthesis of β‐indolyl cyclopentenamides, a versatile chiral building block, by asymmetric addition of indoles to α,β‐unsaturated iminium intermediates has been achieved through chiral anion catalysis. Key to the success of this methodology is the generation of a chiral anion‐paired ketone‐type α,β‐unsaturated iminium intermediate from α‐hydroxy enamides. Preliminary mechanistic studies and DFT calculations are consistent with a mechanism involving multiple, concurrent pathways for isomerization of the initially formed azaallylcation into the key α,β‐unsaturated iminium intermediate, all mediated by the phosphoric acid catalyst.