nowadays nmr spectroscopy becomes a powerful tool in chemistry because of the nmr chemical shifts. hartree–fock theory and the gauge-including atomic orbital (giao) methods are used in the calculation of 29si nmr chemical shifts of various silicate species in the silicate solution as initial components for zeolite synthesis both in gas and solution phase. calculations have been performed at geo...

nowadays nmr spectroscopy becomes a powerful tool in chemistry because of the nmr chemical shifts. hartree–fock theory and the gauge-including atomic orbital (giao) methods are used in the calculation of 29si nmr chemical shifts of various silicate species in the silicate solution as initial components for zeolite synthesis both in gas and solution phase. calculations have been performed at geo...

Molecular orbital calculations at the HF/6-31G(d) level were carried out for polyboric acids and polyborate anions up to a pentamer to estimate their B-to-B isotopic reduced partition function ratios (RPFRs) and examine the additivity of logarithms of RPFRs. Approximate RPFR-values calculated by the use of the additivity agreed with exact RPFR-values within a margin of 1% error. This error was ...

A set of chemical reactions is proposed to account for the formation of pantothenic acid derivatives from a primeval atmosphere composed of ammonia, formaldehyde, propyne, ethyne, hydrogen sulfide, hydrogen and water. Three precursor molecules are initially formed; a di-adduct of propyne and the catalyst Mg.porphin, azetidine2one, and 2-amino ethyl mercaptan. These then react sequentially to fo...

The structure of single walled armchair and zig-zag carbon nanotubes having 70 atoms and two carbons replaced by boron or nitrogen is obtained at minium energy using HF/6-31G* molecular orbital theory. The calculations show that the ground state of the zig-zag tubes is a triplet state while for the armchair tubes it is a singlet. In the zig-zag tubes the density of states at the Fermi level is ...

The vibrational frequencies of N-benzoyl glycine in the ground state have been calculated using density functional method (B3LYP) by using 6-311++G(d,p) basis set. Theoretical vibrational spectra have been interpreted by means of potential energy distribution (PEDs) using MOLVIB program. The equilibrium geometry and the thermodynamic functions of the title compound have been performed at HF/6-3...

The reactants, clusters, transition structures, and products for thevarious channels for the thermal decomposition of SiHkCl,, were optimized at the HF/6-31G(d) and MP2/6-31G(d,p) levels. The electron correlation contributions were calculated at the MP4/6-3 lG(d,p), MP4/6-31+G(Zdf,p), MP2/6-31 ++G(3df,3pd), and G-2 levels of theory. In the decomposition of SiH4, SiH2 + H2 is favored over SiH3 +...

Ab initio and DFT methods have been used to study the seven tautomeric forms of 5-methylcytosine molecule.The related tautomer in gas phase have been studied at HF/6-31G, HF/6-31G* and B3LYP/6-31G* levels oftheory. The structures,enthalpies,entropies,Gibbs free energies,relative tautomerization energies of tautomersand tautomeric equilibrium constants were compared and analyzed along with full ...

Ab initio HF/6-3 lG(d. p) and density functional theory B3LYP/6-31G (d, p) calculations were carried out to investigate the conformations of pyrrolidinium ion. Two conformations, corresponding to twisted (C2) and envelope (Cs) forms were optimized. Vibrational analysis showed that the twisted form is at a local minimum point and the envelope form at a saddle point. The energy difference between...

The internal strain in cyclic amides are explained as a factor of resonance that are effected on the bond length C-N  and are a major factor of rates of hydrolysis. The cyclic amides in this study are optimized by Gaussian program and the bond length of C-N in the rings are studied by HF/6-31G*.