Quantum Chemical Computations (quantum + chemical_computation)

Distribution by Scientific Domains


Selected Abstracts


Ab initio energy calculations and macroscopic rate modeling of hydroformylation of higher alkenes by Rh-based catalyst

AICHE JOURNAL, Issue 12 2009
Maizatul S. Shaharun
Abstract Ab initio quantum chemical computations have been done to determine the energetics and reaction pathways of hydroformylation of higher alkenes using a rhodium complex homogeneous catalyst. Calculation of fragments of the potential energy surfaces of the HRh(CO)(PPh3)3 -catalyzed hydroformylation of 1-decene, 1-dodecene, and styrene were performed by the restricted Hartree-Fock method at the second-order MØller-Plesset (MP2) level of perturbation theory and basis set of 6-31++G(d,p). Geometrically optimized structures of the intermediates and transition states were identified. Three generalized rate models were developed on the basis of above reaction path analysis as well as experimental findings reported in the literature. The kinetic and equilibrium parameters of the models were estimated by nonlinear least square regression of available literature data. The model based on H2 -oxidative addition fitted the data best; it predicts the conversion of all the alkenes quite satisfactorily with an average deviation of 7.6% and a maximum deviation of 13%. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]


Surface enhanced Raman scattering of trans-p-coumaric and syringic acids

JOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009
R. E. Clavijo
Abstract The vibrational spectra of trans-p-coumaric acid (pCA) and syringic acid (SA) are discussed. The spectral fingerprints of the organic acids observed in the infrared and Raman spectra are assigned to fundamental vibrational wavenumbers supported by quantum chemical computations. The average surface-enhanced Raman scattering spectra of both acids have been obtained on silver colloidal solutions and the interpretation of the spectra is presented based on complementary Raman spectra and computational results for the silver salts. Copyright © 2009 John Wiley & Sons, Ltd. [source]


The structural elucidation of a novel iridoid derivative from Tachiadenus longiflorus (Gentianaceae) using the LSD programme and quantum chemical computations

PHYTOCHEMICAL ANALYSIS, Issue 2 2006
D. A. Mulholland
Abstract Oleanolic acid, scoparone, scopoletin and a novel iridoid derivative, angelone, were isolated from Tachiadenus longiflorus (Gentianaceae). The structure of angelone was determined from NMR data, given as input to the Logic for Structure Determination Programme, and was finally confirmed by comparison of experimental 13C-NMR chemical shifts with those obtained by quantum mechanical calculations. Copyright © 2005 John Wiley & Sons, Ltd. [source]


Calculation of the Detonation Velocities and Detonation Pressures of Dinitrobiuret (DNB) and Diaminotetrazolium Nitrate (HDAT-NO3)

PROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 1 2004
Janna Geith
Abstract The enthalpies of combustion (,combH) of dinitrobiuret (DNB) and diaminotetrazolium nitrate (HDAT-NO3) were determined experimentally using oxygen bomb calorimetry: ,combH(DNB)=5195±200,kJ kg,1, ,combH(HDAT-NO3)=7900±300,kJ kg,1. The standard enthalpies of formation (,fH°) of DNB and HDAT-NO3 were obtained on the basis of quantum chemical computations at the electron-correlated ab initio MP2 (second order Møller-Plesset perturbation theory) level of theory using a correlation consistent double-zeta basis set (cc-pVTZ): ,fH°(DNB)=,353,kJ mol,1, ,1,829,kJ kg,1; ,fH°(HDAT-NO3)=+254,kJ mol,1, +1,558,kJ kg,1. The detonation velocities (D) and detonation pressures (P) of DNB and HDAT-NO3 were calculated using the empirical equations by Kamlet and Jacobs: D(DNB)=8.66,mm,,s,1, P(DNB)=33.9,GPa, D(HDAT-NO3)=8.77,mm,,s,1, P(HDAT-NO3)=33.3,GPa. [source]


Enhanced Fluorescence of Remote Functionalized Diaminodicyanoquinodimethanes in the Solid State and Fluorescence Switching in a Doped Polymer by Solvent Vapors

CHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2004
S. Jayanty
Abstract Remote functionalized zwitterionic diaminodicyanoquinodimethanes are found to exhibit a dramatic enhancement of light emission in the solid state and when doped in polymer films, as compared to the solution state. Crystal structure analysis of prototypical molecules reveals the role of the remote functionality in the solid state molecular organization. Semiempirical quantum chemical computations provide a viable model to explain the interesting phenomenon of fluorescence enhancement as arising from the inhibition of geometry relaxation of the vertical excited state to a nonemitting state. The reversible switching of a doped polymer film fluorescence triggered by solvent vapors is demonstrated. [source]