Reactions of a-Oxo Ketenes with Amides: Experimental Data and Semiempirical AM1 Molecular Orbital Calculations

Heterocycles ◽  
2002 ◽  
Vol 57 (8) ◽  
pp. 1445 ◽  
Author(s):  
Emin Saripinar ◽  
Ilhan Ozer Ilhan ◽  
Yunus Akçamur
Keyword(s):  
Experimental Data ◽  
Molecular Orbital ◽  
Molecular Orbital Calculations

Nitrosyl cyanide and related aspects of the ONCN potential surface

1978 ◽  
Vol 31 (11) ◽  
pp. 2349 ◽  
Author(s):  
BG Gowenlock ◽  
L Radom
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Related Species ◽  
Potential Surface ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Hartree Fock ◽  
Split Valence ◽  
Good Agreement

Ab initio molecular orbital calculations using the restricted Hartree-Fock approach have been carried out for nitrosyl cyanide and related species on the ONCN potential surface. Full geometry optimizations have been performed with the minimal STO-3G and split-valence 4-31G basis sets. Calculated (4-31G) geometries are in good agreement with available experimental data as are the energy changes in the reactions ONCN → NO + CN and NO + CN → N2 + CO. Possible mechanisms are discussed.

CHEMICAL EFFECT ON X-RAY FLUORESCENCE YIELDS FOR CARBON

1996 ◽  
Vol 06 (03n04) ◽  
pp. 447-452
Author(s):  
TAKESHI MUKOYAMA ◽  
HIROHIDE NAKAMATSU ◽  
HIROHIKO ADACHI
Keyword(s):  
Experimental Data ◽  
Simple Model ◽  
Molecular Orbital ◽  
Fluorescence Yield ◽  
Chemical Effect ◽  
Molecular Orbital Calculations ◽  
Effective Number ◽  
Scaling Method ◽  
X Ray ◽  
Carbon Compounds

The chemical effect on K-shell fluorescence yields for carbon compounds has been estimated in a simple model based on the discrete-variational Xα molecular orbital calculations and the statistical scaling method. The calculated results show that there is a relation between the fluorescence yield and the effective number of 2p electrons in carbon, n2p. The behavior of the fluorescence yield as a function of n2p is in qualitatively agreement with the experimental data by proton impact. The present values for fluorescence yields of carbon oxides agree with other theoretical values.

Applications of Molecular Dynamics Simulations to Sol-Gel Processing

1986 ◽  
Vol 73 ◽  
Author(s):  
S. H. Carofalini ◽  
H. Melman
Keyword(s):  
Experimental Data ◽  
Molecular Dynamics ◽  
Computer Simulation ◽  
Molecular Dynamics Simulations ◽  
Molecular Orbital ◽  
Sol Gel ◽  
Molecular Orbital Calculations ◽  
Computer Simulation Technique ◽  
Dynamics Simulations ◽  
Gel Processing

ABSTRACTThe molecular dynamics computer simulation technique has been used to study silicic acid and pyrosilicic acid molecules (H4 SiO4 and H6 Si 2 O7, respectively). The structure of the simulated molecules are compared to those found by molecular orbital calculations as well as structures inferred from silicate hydrates. The potentials used to simulate the molecules were also used in simulations of bulk silicates and compared with experimental data. Results indicate good correlation.

The Perlin Effect: bond lengths, bond strengths, and the origins of stereoelectronic effects upon one-bond C–H coupling constants

1990 ◽  
Vol 68 (7) ◽  
pp. 1051-1062 ◽  
Author(s):  
Saul Wolfe ◽  
B. Mario Pinto ◽  
Vikram Varma ◽  
Ronald Y. N. Leung
Keyword(s):  
Experimental Data ◽  
Bond Length ◽  
Molecular Orbital ◽  
Global Analysis ◽  
Coupling Constants ◽  
Molecular Orbital Calculations ◽  
Anomeric Effect ◽  
Coupling Constant ◽  
Electron Pairs ◽  
Bond Lengths

The magnitude of a one-bond C–H coupling constant depends upon the chemical environment of the hydrogen atom and, especially, upon its stereochemical relationship to vicinal lone electron pairs. However, a lone electron pair is not essential for the observation of a stereoelectronic effect, since even cyclohexane exhibits different axial and equatorial C–H coupling constants. We propose the name "Perlin Effect" to describe such observations. An analysis of the extensive experimental data regarding the Perlin Effect reveals that, in cyclohexane and in six-membered rings having one or more heteroatoms of the first row attached to the carbon of interest, 1JC–H is always larger for an equatorial hydrogen than for an axial hydrogen. The magnitude of the Perlin Effect is reduced when the carbon carrying the hydrogen of interest is attached to first row and second row atoms or heteroatoms, and it reverses when the carbon atom carries two heteroatoms from below the first row.The existence of the Perlin Effect in nuclear magnetic resonance spectra is reminiscent of an infrared effect known as the Bohlmann bands, whose origin has previously been explained by quantitative perturbational molecular orbital (PMO) theory in terms of the effects of lone electron pairs upon the lengths and strengths and, therefore, the chemical reactivities of vicinal C—H bonds. Since the magnitude of a one-bond C–H coupling constant is expected to vary inversely with bond length, the origins of the Perlin Effect and of the Bohlmann bands would seem to be the same, i.e., the longer (weaker) C—H bond has the smaller one-bond coupling constant. This expectation has now been confirmed: for 25 molecules, representing a total of 35 different kinds of C—H bonds, the bond lengths, stretching force constants, and charge distributions have been determined from fully optimized 6-31G* molecular orbital calculations. In nine of ten cases for which experimental data exist for pairs of diastereomeric or diastereotopic hydrogens, the shorter C—H bond of the pair has the larger coupling constant; in the tenth case, the experimental difference is only 1–2 Hz. Moreover, a global analysis of the data in terms of the equation J = A + BqCqH + C/r, where J is an experimental coupling constant, q is a total atomic charge, and r is a C—H bond length, correlates 23 different types of C—H bonds linearly with a correlation coefficient of 0.915. The C parameter is the leading term of the correlation. Among the systems studied theoretically are eight molecules of the type CH3CHXY (Y = OH, SH; X = F, Cl, OH, SH), which are representative of systems containing both endocyclic and exocyclic first row and second row anomeric effects. The exocyclic effect is found to be very similar for first row and second row substituents, but the endocyclic effect is larger for the first row substituent. Both findings agree with experimental data in solution. Finally, quantitative PMO analysis has been employed to analyse the origins of the different C—H bond lengths in the various molecules of the study. Keywords: anomeric effect, PMO analysis, NMR, stereochemistry, molecular orbital calculations.

Interactions between Methylene Blue and Pullulan According to Molecular Orbital Calculations

2020 ◽  
Vol 140 (11) ◽  
pp. 529-533
Author(s):  
Pasika Temeepresertkij ◽  
Saranya Yenchit ◽  
Michio Iwaoka ◽  
Satoru Iwamori
Keyword(s):  
Methylene Blue ◽  
Molecular Orbital ◽  
Molecular Orbital Calculations

A pairwise additivity scheme for conformational energies of substituted ethanes

1975 ◽  
Vol 343 (1632) ◽  
pp. 1-10 ◽  
Keyword(s):  
Large Deviations ◽  
Ab Initio ◽  
Dihedral Angle ◽  
Molecular Orbital ◽  
Methyl Groups ◽  
Molecular Orbital Calculations ◽  
Linear Combinations ◽  
Strongly Interacting ◽  
Conformational Energies

Ab initio molecular orbital calculations are used to explore additivity in the conformational energies of poly-substituted ethanes in terms of conformational energies of ethane and appropriate mono- and 1,2-di-substituted derivatives. Such relations would allow complex calculations for poly-substituted ethanes to be replaced by much simpler ones on a small number of parent molecules. General expressions for the linear combinations are derived from the assumption that interactions between vicinal substituents are pairwise additive and depend only on the vicinal dihedral angle. The additivity scheme is tested for 15 ethanes, di-, tri- or tetrasubstituted by cyano and methyl groups and for a smaller number of fluoroethanes. Additivity applies to within 0.1- 0.3 k J mol -1 in the methylethanes and mostly to within about 0.7- 0.8 kJ mol -1 in cyanoethanes. Large deviations are found among the geminally substituted fluoroethanes. It is suggested that the additivity approximation is most successful in the absence of strongly interacting geminal groups. Predictions are made of conformational energies of ten hexa(cyano- and methyl-) substituted ethanes.

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