Conformational equilibria in some cyclic imines: NH and CH stretching vibrations and the axial lone pair

1970 ◽  
Vol 48 (20) ◽  
pp. 3236-3248 ◽  
Author(s):  
P. J. Krueger ◽  
J. Jan
Keyword(s):  
Lone Pair ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Trans Orientation ◽  
Methyl Substitution ◽  
Lone Pair Orbital ◽  
Conformational Equilibria ◽  
Solvent Environment ◽  
Stretching Vibrations ◽  
Lone Pair Electrons

The fundamental NH and CH stretching vibrations of a number of cyclic imines have been examined in dilute CC14 solution. A trans orientation of the N lone pair orbital and one or more hydrogen atoms on adjacent carbons lowers the relevant vCH ("Bohlmann" bands) and raises vNH reflecting an increase in the s-character of the CH bond(s), consistent with a partial delocalization of the lone pair electrons into the CN bond. Conformations in which this interaction occurs are thermodynamically favored, and the ΔH values for the lone pair axial–equatorial equilibrium in piperidine, pyrrolidine, and indolene are estimated to be 0.4, 0.2, and 0.1 kcal/mole, respectively, in dilute CCl4 solution.The effects of hetero ring size, N-substitution, α-methyl substitution, and the solvent environment are investigated.

The molecular orbital theory of chemical valency. V. The structure of water and similar molecules

1950 ◽  
Vol 202 (1070) ◽  
pp. 323-336 ◽  
Keyword(s):  
Spatial Distribution ◽  
Equilibrium Configuration ◽  
Bond Angle ◽  
Lone Pair ◽  
Orbital Theory ◽  
Hydrogen Atoms ◽  
Molecular Formation ◽  
Major Factors ◽  
Lone Pair Electrons ◽  
Electrostatic Repulsions

The theory of molecular and equivalent orbitals developed in previous papers of this series is used to discuss the spatial distribution of lone-pair electrons in molecules such as H 2 O and NH 3 and the part they play in determining the equilibrium configuration. Previous treatments of H 2 O have assumed that the lone pairs are essentially unaltered by molecular formation. It is shown here, on the other hand, that they will be displaced so as to be mainly concentrated on the side of the O-nucleus remote from the hydrogen atoms. An important consequence of this is that the lone-pair electrons will make a contribution to the total dipole moment. Comparison of the experimentally observed moment with an approximate quantitative treatment suggests that, as a result of this, transfer of electrons from the hydrogen atoms to the oxygen does not occur to the extent that has previously been believed. The variation of the spatial distribution of the orbitals of H 2 O with changes of nuclear configuration is examined and it is shown that, in the equilibrium position, the electronic structure can be described approximately by two sets of two equivalent orbitals pointing in nearly tetrahedral directions. The dependence of total energy on bond angle is discussed and it is shown that electrostatic repulsions between the equivalent orbitals are major factors in determining the equilibrium configuration. Similar considerations apply to NH 3 .

Amino group stretching vibrations in primary aliphatic amines

1967 ◽  
Vol 45 (14) ◽  
pp. 1605-1610 ◽  
Author(s):  
P. J. Krueger ◽  
D. W. Smith
Keyword(s):  
Alkyl Chain ◽  
Inductive Effect ◽  
Lone Pair ◽  
Aliphatic Amines ◽  
Lone Pair Orbital ◽  
First Approximation ◽  
Symmetric Band ◽  
Integrated Intensity ◽  
Stretching Vibrations ◽  
Primary Aliphatic Amines

Primary aliphatic amines can be characterized by infrared spectroscopy as to the nature and degree of branching of the alkyl chain, using the fundamental antisymmetric and symmetric NH2 stretching frequencies measured in dilute C2Cl4 solution. Where steric and direct conjugation effects are absent both frequencies and the integrated intensity of the antisymmetric band increase linearly with decreasing inductive electron-donating power of the alkyl chain. The integrated intensity of the symmetric band, which is smaller than that for the antisymmetric band in all the 26 compounds studied, is independent of the inductive nature of the alkyl chain as a first approximation. These results indicate that the N-atom lone-pair orbital in RNH2 plays a negligibly small role in modifying the inductive effect of R on NH2 frequencies and intensities as long as the N-atom hybridization remains sp3.

The surface chemistry of kaolinite. II. Catalysis of n-butane decomposition

1972 ◽  
Vol 25 (9) ◽  
pp. 1843 ◽  
Author(s):  
AS Buchanan ◽  
RC Oppenheim
Keyword(s):  
Catalytic Activity ◽  
Lone Pair ◽  
Acid Leaching ◽  
Hydroxyl Groups ◽  
Surface Oxygen ◽  
Hydrogen Atoms ◽  
Before And After ◽  
Hydrocarbon Reactions ◽  
Lone Pair Electrons ◽  
Oxygen Atoms

The catalytic activity of kaolinite before and after acid leaching for the decomposition of n-butane between 669 and 727 K has been compared with that of alumina natural and precipitated, and silica. The catalysis of hydrocarbon reactions on oxide surfaces appears to involve oxygen atoms which may be attached to the solid surface either physically adsorbed as the gas, as part of the lattice, or possibly as attached hydroxyl groups. Dehydrogenation of the hydrocarbon appears to be the first important step, suggesting that adsorption of the reactant involves interaction of the hydrogen atoms with lone pair electrons of surface oxygen atoms.

Effect of delocalization of nonbonding electron density on the stability of the M–Ccarbene bond in main group metal-imidazol-2-ylidene complexes: a computational and structural database study

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Samuel Tetteh ◽  
Albert Ofori
Keyword(s):  
Electron Density ◽  
Lone Pair ◽  
Main Group ◽  
Binding Energies ◽  
Electrostatic Model ◽  
Group Metal ◽  
Main Group Metal ◽  
Structural Database ◽  
The Stability ◽  
Lone Pair Electrons

Abstract The M–Ccarbene bond in metal (M) complexes involving the imidazol-2-ylidene (Im) ligand has largely been described using the σ-donor only model with donation of σ electrons from the sp-hybridized orbital of the carbene carbon into vacant orbitals on the metal centre. Analyses of the M–Ccarbene bond in a series of group IA, IIA and IIIA main group metal complexes show that the M-Im interactions are mostly electrostatic with the M–Ccarbene bond distances greater than the sum of the respective covalent radii. Estimation of the binding energies of a series of metal hydride/fluoride/chloride imidazol-2-ylidene complexes revealed that the stability of the M–Ccarbene bond in these complexes is not always commensurate with the σ-only electrostatic model. Further natural bond orbital (NBO) analyses at the DFT/B3LYP level of theory revealed substantial covalency in the M–Ccarbene bond with minor delocalization of electron density from the lone pair electrons on the halide ligands into antibonding molecular orbitals on the Im ligand. Calculation of the thermodynamic stability of the M–Ccarbene bond showed that these interactions are mostly endothermic in the gas phase with reduced entropies giving an overall ΔG > 0.

scholarly journals Long-term stability in γ-CsPbI3 perovskite via an ultraviolet-curable polymer network

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Nam-Kwang Cho ◽  
Hyun-Jae Na ◽  
Jeeyoung Yoo ◽  
Youn Sang Kim
Keyword(s):  
Polymer Network ◽  
Lone Pair ◽  
Ambient Conditions ◽  
Absorption Properties ◽  
Term Stability ◽  
Long Term Stability ◽  
Ultraviolet Curable ◽  
Oxygen Lone Pair ◽  
Lone Pair Electrons

AbstractBlack-colored (α, γ-phase) CsPbI3 perovskites have a small bandgap and excellent absorption properties in the visible light regime, making them attractive for solar cells. However, their long-term stability in ambient conditions is limited. Here, we demonstrate a strategy to improve structural and electrical long-term stability in γ-CsPbI3 by the use of an ultraviolet-curable polyethylene glycol dimethacrylate (PEGDMA) polymer network. Oxygen lone pair electrons from the PEGDMA are found to capture Cs+ and Pb2+ cations, improving crystal growth of γ-CsPbI3 around PEGDMA. In addition, the PEGDMA polymer network strongly contributes to maintaining the black phase of γ-CsPbI3 for more than 35 days in air, and an optimized perovskite film retained ~90% of its initial electrical properties under red, green, and blue light irradiation.

VUV FRAGMENTATION OF SOME HYDROFLUOROCARBON CATIONS STUDIED USING COINCIDENCE TECHNIQUES

2002 ◽  
Vol 09 (01) ◽  
pp. 153-158 ◽  
Author(s):  
WEIDONG ZHOU ◽  
D. P. SECCOMBE ◽  
R. Y. L. CHIM ◽  
R. P. TUCKETT
Keyword(s):  
Kinetic Energy ◽  
Ab Initio ◽  
Ground State ◽  
Lower Energy ◽  
Lone Pair ◽  
Electronic States ◽  
Photoelectron Spectra ◽  
Highest Occupied Molecular Orbital ◽  
Impulsive Model ◽  
Lone Pair Electrons

Threshold photoelectron–photoion coincidence (TPEPICO) spectroscopy has been used to investigate the decay dynamics of the valence electronic states of the parent cation of several hydrofluorocarbons (HFC), based on fluorine-substituted ethane, in the energy range 11–25 eV. We present data for CF 3– CHF 2, CF 3– CH 2 F , CF 3– CH 3 and CHF 2– CH 3. The threshold photoelectron spectra (TPES) of these molecules show a common feature of a broad, relatively weak ground state, associated with electron removal from the highest-occupied molecular orbital (HOMO) having mainly C–C σ-bonding character. Adiabatic and vertical ionisation energies for the HOMO of the four HFCs are presented, together with corresponding values from ab initio calculations. For those lower-energy molecular orbitals associated with non-bonding fluorine 2pπ lone pair electrons, these electronic states of the HFC cation decay impulsively by C–F bond fission with considerable release of translational kinetic energy. Appearance energies are presented for formation of the daughter cation formed by such a process (e.g. CF 3– CHF +), together with ab initio energies of the corresponding dissociation channel (e.g. CF 3– CHF + + F ). Values for the translational kinetic energy released are compared with the predictions of a pure-impulsive model.

p-Type conductivity of GeTe: The role of lone-pair electrons

2012 ◽  
Vol 249 (10) ◽  
pp. 1902-1906 ◽  
Author(s):  
Alexander V. Kolobov ◽  
Paul Fons ◽  
Junji Tominaga
Keyword(s):  
Lone Pair ◽  
Type Conductivity ◽  
P Type ◽  
Lone Pair Electrons

The photochemical and thermal decompositions of hydrogen sulphide

1953 ◽  
Vol 216 (1126) ◽  
pp. 344-361 ◽  
Keyword(s):  
Thermal Decomposition ◽  
Quantum Yield ◽  
Hydrogen Sulphide ◽  
Low Temperatures ◽  
Room Temperature ◽  
Large Fraction ◽  
Kcal Mole ◽  
Hydrogen Atoms ◽  
Photochemical Decomposition ◽  
Bimolecular Mechanism

The photochemical decomposition of hydrogen sulphide has been investigated at pressures between 8 and 550 mm of mercury and at temperatures between 27 and 650° C, using the narrow cadmium line ( λ 2288) and the broad mercury band (about λ 2550). At room temperature the quantum yield increases with pressure from 1.09 at 30 mm to 1.26 at 200 mm. Above 200 mm pressure there was no further increase in the quantum yield. Temperature had little effect on the quantum yield at λ 2550, but there was a marked increase in the rate of hydrogen production between 500 and 650° C with 2288 Å radiation. This may have been caused by the decomposition of excited hydrosulphide radicals. The results are consistent with a mechanism involving hydrogen atoms and hydrosulphide radicals. The mercury-photosensitized reaction is less efficient than the photochemical decomposition, the quantum yield being only about 0.45. The efficiency increased with temperature and approached unity at high temperatures and pressures. This agrees with the suggestion that a large fraction of the quenching collisions lead to the formation of Hg ( 3 P 0 ) atoms. The thermal decomposition is heterogeneous at low temperatures and becomes homogeneous and of the second order at 650° C. The experimental evidence suggests the bimolecular mechanism 2H 2 S → 2H 2 + S 2 . The activation energies are 25 kcal/mole (heterogeneous) and 50 kcal/mole (homogeneous).

Synergistic optimization of carrier transport and thermal conductivity in Sn-doped Cu2Te

2018 ◽  
Vol 6 (39) ◽  
pp. 18928-18937 ◽  
Author(s):  
Yuchong Qiu ◽  
Ying Liu ◽  
Jinwen Ye ◽  
Jun Li ◽  
Lixian Lian
Keyword(s):  
Thermal Conductivity ◽  
Fermi Level ◽  
Carrier Concentration ◽  
Power Factor ◽  
Carrier Transport ◽  
Lone Pair ◽  
Thermoelectric Performance ◽  
Degenerate Semiconductors ◽  
Lone Pair Electrons

Doping Sn into the Cu2Te lattice can synergistically enhance the power factor and decrease thermal conductivity, leading to remarkably optimized zTs. The lone pair electrons from the 5s orbital of Sn can increase the DOS near the Fermi level of Cu2Te to promote PF and reduce κe by decreasing the carrier concentration. This study explores a scalable strategy to optimize the thermoelectric performance for intrinsically highly degenerate semiconductors.

Dipole Moment as a Possible Diagnostic Descriptor of the Conformational Isomerism of the Ammonia Molecule

2012 ◽  
pp. 58-75
Author(s):  
Dulal C. Ghosh ◽  
Sandip Kumar Rajak
Keyword(s):  
Dipole Moment ◽  
Equilibrium Shape ◽  
Lone Pair ◽  
Molecular Orbitals ◽  
Energy Curve ◽  
Conformational Isomerism ◽  
Localized Molecular Orbitals ◽  
Time Symmetry ◽  
Quantum Mechanical Study ◽  
Lone Pair Electrons

In this report, Ghosh and Rajak have made a detailed quantum mechanical study of the variation of the dipole moment of ammonia as a function of its conformations evolving during the process of its umbrella inversion by invoking their method of dipole correlation of electronic structure as basis. Ghosh et al discover a surprising result that the variation of dipole moment mimics the total energy curve as a function of reaction coordinates revealing the fact that the dipole moment is one possible diagnostic descriptor of the conformational isomerism of molecules containing lone pair electrons. The dipole is calculated and partitioned into bond and lone pair components for a large number of conformations between the equilibrium shape and the transition state of inversion and the results are interpreted and correlated in terms of the localized molecular orbitals, LMOs generated from the canonical molecular orbitals, CMO’s of each conformation. Anderson, from the concept of space time symmetry, postulated that ammonia has zero dipole moment. Present study reveals that Anderson’s correlation relied upon the bond moment only while the major component of dipole of ammonia originates from the lone pair of nitrogen.

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