Substituent effects in carbocations CX+, CHX+•, and CH2X+, and in singlet and triplet carbenes CHX. Proton affinities of singlet carbenes

1985 ◽  
Vol 63 (12) ◽  
pp. 3582-3586 ◽  
Author(s):  
A. C. Hopkinson ◽  
M. H. Lien
Keyword(s):  
Energy Gap ◽  
Single Point ◽  
Substituent Effects ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Proton Affinities ◽  
Interaction Method ◽  
Triplet Energy ◽  
Configuration Interaction Method ◽  
Singlet Carbenes

Abinitio molecular orbital calculations with a 6-31G* basis set have been used to optimise structures for CX+, CHX+•, CHX (both singlets and triplets), H2CX+ and H3CX (X = H, CH3, NH2, OH, F, CN, and NC). Single point calculations were then performed on the 6-31G* optimised structures using a configuration interaction method involving all single and double excitations from the valence shell. Stabilisation energies for the carbocations are compared with those already reported for H2CX+. For the carbenes the single-triplet energy gap is examined as a function of substituent and the stabilisation energies of the singlet carbenes are compared with those of the isoelectronic carbocations H2CX+. Proton affinities are reported for the singlet carbenes and are compared with the proton affinities of similarly substituted ethylenes, H2C=CHX.

Theoretical investigation on tautomerism and NLO properties of Salicylideneaniline derivatives

2021 ◽  
Author(s):  
N. Daho ◽  
N. Benhalima ◽  
F. KHELFAOUI ◽  
O. SADOUKI ◽  
M. Elkeurti ◽  
...  
Keyword(s):  
Optical Properties ◽  
Density Functional ◽  
Energy Gap ◽  
Intramolecular Proton Transfer ◽  
Basis Set ◽  
Frontier Molecular Orbital ◽  
Molecular Orbital Calculations ◽  
Visible Absorption ◽  
Charge Delocalization ◽  
Intramolecular Hydrogen

In this work, a comprehensive investigation of the salicylideneaniline derivatives is carried out using density functional theory to determine their linear and non-linear optical properties. Geometry optimizations, for gas and solvent phases, of the tautomers (enol and keto forms) are calculated using B3LYP levels with 6–31G (d,p) basis set . An intramolecular proton transfer, for 1SA-E and 2SA-E, is performed by a PES scan process at the B3LYP/6-31G (d,p) level. The optical properties are determined and show that they have extremely high nonlinear optical properties. In addition, the RDG analysis, MEP, and gap energy are calculated. The low energy gap value indicates the possibility of intramolecular charge transfer. The frontier molecular orbital calculations clearly show the inverse relationship of HOMO–LUMO gap with the first-order hyperpolarizability (β = 59.6471 × 10-30 esu), confirming that the salicylideneaniline derivatives can be used as attractive future NLO materials. Therefore, the reactive sites are predicted using MEP and the visible absorption maxima are analyzed using a theoretical UV–Vis spectrum. Natural bond orbitals are used to investigate the stability, charge delocalization, and intramolecular hydrogen bond.

1H nuclear magnetic resonance and molecular orbital studies of the conformations of 3-fluoroanisole

1989 ◽  
Vol 67 (6) ◽  
pp. 1027-1031 ◽  
Author(s):  
Ted Schaefer ◽  
Rudy Sebastian
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Orbital ◽  
Substituent Effects ◽  
Spin Coupling ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Minimal Basis ◽  
Parent Molecule ◽  
Nuclear Magnetic

The proximate spin–spin coupling constant between the methyl protons and the ring protons, 5J(H,OCH3), is extracted from a full analysis of the 1H and 19F nuclear magnetic resonance spectra of 3-fluoroanisole in CS2 and acetone-d6 solutions. The values of 5J(H,OCH3) imply that the less polar cis conformer is slightly more stable at 300 K than the more polar trans conformer in both solvents, in agreement with geometry-optimized STO-3G MO computations for the free molecule. The latter also find a higher barrier to internal rotation of the methoxy group for 3-fluoroanisole than for the parent molecule. The present results are compared with other measurements of the conformer ratio for the vapor and for solutions. The STO-3G and 6-31G structures of the cis and trans conformers are compared. The C—F bond length is computed more reliably with the minimal basis set, as is the COC bond angle. The internal angles of the benzene moiety are, of course, found more accurately with the 6-31G basis. The computations indicate additivity of the substituent effects on the internal angle, as found experimentally for a variety of benzene derivatives. Keywords: 1H NMR of fluoroanisole, conformations of fluoroanisole, molecular orbital calculations for fluoroanisole.

Substituent effects at silicon in cations SiX+, HSiX+•, and H2SiX+, and in radicals H2SiX+•

1989 ◽  
Vol 67 (6) ◽  
pp. 991-997 ◽  
Author(s):  
A. C. Hopkinson ◽  
M. H. Lien
Keyword(s):  
Linear Relationship ◽  
Molecular Orbital ◽  
Single Point ◽  
Substituent Effects ◽  
Molecular Orbital Calculations ◽  
Amino Group ◽  
Ionisation Potential ◽  
Silyl Radicals

Abinitio molecular orbital calculations at the 6-31G* level have been used to optimise structures for ions SiX+, HSiX+•, and H2SiX+, and for neutrals HSiX (singlets), H2SiX•, and H3SiX, where X is H, CH3, NH2, OH, F, CN, and NC. Single point calculations at the MP4(SDTQ)/6-31G* level were used to calculate substituent stabilisation energies.The amino group is the strongest π-donor and also is the most stabilising group in the cations, the silylenes, and the silyl radicals. Stabilisation is greatest in ions SiX+. Ions HSiX+• and H2SiX+ are stabilised by similar but smaller amounts, although CN and NC are destabilising in these ions. Substituent stabilisation energies in radicals H2SiX• are almost zero. There is a linear relationship between the stabilisation energies of ions H2SiX+ and the ionisation potentials of radicals H2SiX•, but a similar plot correlating stabilisation energies for ions HSiX+۟• with the ionisation potential of HSiX (singlet) shows considerable scatter. Keywords: silications, silyl radicals, stabilisation energies.

scholarly journals (E)-1-(Benzo[d][1,3]dioxol-5-yl)-3-([2,2′-bithiophen]-5-yl)prop-2-en-1-one: crystal structure, UV–Vis analysis and theoretical studies of a new π-conjugated chalcone

2019 ◽  
Vol 75 (5) ◽  
pp. 632-637
Author(s):  
Ainizatul Husna Anizaim ◽  
Muhamad Fikri Zaini ◽  
Muhammad Adlan Laruna ◽  
Ibrahim Abdul Razak ◽  
Suhana Arshad
Keyword(s):  
Density Functional ◽  
Energy Gap ◽  
Weak Interactions ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Functional Theory ◽  
Compound C ◽  
Homo And Lumo ◽  
Experimental Values ◽  
Homo Lumo

In the title compound, C18H12O3S2, synthesized by the Claisen–Schmidt condensation method, the essentially planar chalcone unit adopts an s-cis configuration with respect to the carbonyl group within the ethylenic bridge. In the crystal, weak C—H...π interactions connect the molecules into zigzag chains along the b-axis direction. The molecular structure was optimized geometrically using Density Functional Theory (DFT) calculations at the B3LYP/6–311 G++(d,p) basis set level and compared with the experimental values. Molecular orbital calculations providing electron-density plots of HOMO and LUMO molecular orbitals and molecular electrostatic potentials (MEP) were also computed both with the DFT/B3LYP/6–311 G++(d,p) basis set. The experimental energy gap is 3.18 eV, whereas the theoretical HOMO–LUMO energy gap value is 2.73 eV. Hirshfeld surface analysis was used to further investigate the weak interactions present.

scholarly journals Exchange Functionals and Basis Set Comparisons for Theoretical Studies of ZnO Nonoclusters

2021 ◽  
Author(s):  
Duwage Perera ◽  
jayendran Rasaiah
Keyword(s):  
Water Splitting ◽  
Density Functional ◽  
Energy Gap ◽  
Wide Band ◽  
Theoretical Method ◽  
Basis Set ◽  
Basis Sets ◽  
Triplet Energy ◽  
Energy Gaps ◽  
Zno Clusters

Catalysts made of nano-scaled metal oxide clusters can push the limits of chemical reactions in the manufacture of paints, cosmetics, and pharmaceuticals. The ZnO clusters can also act as semiconductors with a wide band gap of 3.4 eV at 300 K, and are prospective phoocatalysts in many reactions including H2 production in water splitting reactions. In this project, we studied the structural (geometry) and electronic properties (vertical detachment energy and electron affinity) of ZnO monomers and dimers that form model ZnO clusters, using density functional theory (DFT) with many different exchange functionals and 29 basis sets to optimize their choice. We compared the singlet-triplet energy gaps of small ZnO clusters to find the optimal ZnO cluster size and the best theoretical method to investigate their photocatalytic water splitting activity. Our results show that B3LYP/DGDZVP2 level of exchange functional/basis set theory is the most efficient and fastest of the ones considered. Comparison of the singlet-triplet energy gaps shows that the trimer (ZnO)3, with an energy gap of 58.66 k cal/mol, is approximately equal to the energy of a visible photon at 555 nm and a HOMO-LUMO gap of 4.4 eV, and is the best choice amongst the (ZnO)n clusters of different sizes when the number of monomers n in the clusters ranges from 1 to 6. We used the Gaussian16 software package for all the calculations.

scholarly journals Exchange Functionals and Basis Set Comparisons for Theoretical Studies of ZnO Nonoclusters

2021 ◽  
Author(s):  
Duwage Perera ◽  
jayendran Rasaiah
Keyword(s):  
Water Splitting ◽  
Density Functional ◽  
Energy Gap ◽  
Wide Band ◽  
Theoretical Method ◽  
Basis Set ◽  
Basis Sets ◽  
Triplet Energy ◽  
Energy Gaps ◽  
Zno Clusters

Catalysts made of nano-scaled metal oxide clusters can push the limits of chemical reactions in the manufacture of paints, cosmetics, and pharmaceuticals. The ZnO clusters can also act as semiconductors with a wide band gap of 3.4 eV at 300 K, and are prospective phoocatalysts in many reactions including H2 production in water splitting reactions. In this project, we studied the structural (geometry) and electronic properties (vertical detachment energy and electron affinity) of ZnO monomers and dimers that form model ZnO clusters, using density functional theory (DFT) with many different exchange functionals and 29 basis sets to optimize their choice. We compared the singlet-triplet energy gaps of small ZnO clusters to find the optimal ZnO cluster size and the best theoretical method to investigate their photocatalytic water splitting activity. Our results show that B3LYP/DGDZVP2 level of exchange functional/basis set theory is the most efficient and fastest of the ones considered. Comparison of the singlet-triplet energy gaps shows that the trimer (ZnO)3, with an energy gap of 58.66 k cal/mol, is approximately equal to the energy of a visible photon at 555 nm and a HOMO-LUMO gap of 4.4 eV, and is the best choice amongst the (ZnO)n clusters of different sizes when the number of monomers n in the clusters ranges from 1 to 6. We used the Gaussian16 software package for all the calculations.

Are Polarized Cyclobutadienes Non-Aromatic?

2000 ◽  
Vol 53 (6) ◽  
pp. 443 ◽  
Author(s):  
Mathias Ugelstad Frederiksen ◽  
Richard Francis Langler ◽  
Keith Jeffery Watson ◽  
Andrea Penwell ◽  
Katherine Valenta Darvesh
Keyword(s):  
Molecular Orbital ◽  
Energy Gap ◽  
Molecular Orbital Calculations ◽  
Triplet Energy ◽  
Mp2 Calculations ◽  
Antiaromatic Character ◽  
Semiempirical Molecular Orbital

A series of non-alternant cyclobutadienes, both hydrocarbon and heteroatom-substituted, are examined by means of PM3 semiempirical molecular orbital calculations. The results show that even very substantial polarization has no simply predictable effect on antiaromatic character as measured by the singlet–triplet energy gap. MP2 calculations on selected hydrocarbons lead to the same conclusion.

Potential Energy Curves and Spectroscopic Properties of C-2 Studied by Configuration Interaction Method

2015 ◽  
Vol 737 ◽  
pp. 105-109
Author(s):  
Wei Xin Shi ◽  
Fei Long Wu ◽  
Chuan Liang Li ◽  
Qing Shi Wang ◽  
Ji Lin Wei
Keyword(s):  
Excited State ◽  
Configuration Interaction ◽  
Single Point ◽  
Spectroscopic Properties ◽  
Basis Sets ◽  
Spectroscopic Constants ◽  
Interaction Method ◽  
Configuration Interaction Method ◽  
Point Energy ◽  
Experimental Values

Using multi reference configuration interaction (MRCI) method, with aug-cc-pV5Z, aug-cc-pv6z, aug-cc-pcv5z, aug-cc-pcv6z basis sets etc., the single point energy of the ground state and the first excited state and second excited state of C-2are calculated. Then LEVEL program is used to fit out the spectroscopic constants of three states. Results obtained by MRCI/aug-cc-pcv5z-dk method are close to the experimental values.

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