Explicit representation of lone‐pair orbitals in molecular orbital calculations for NH3, H2O, N2H4, and H2O2

1977 ◽  
Vol 67 (11) ◽  
pp. 4787-4793 ◽  
Author(s):  
P. Barry Ryan ◽  
H. David Todd
Keyword(s):  
Molecular Orbital ◽  
Lone Pair ◽  
Explicit Representation ◽  
Molecular Orbital Calculations

INDO Molecular Orbital Calculations of Nitrogen–Proton Spin–Spin Coupling Constants Over Two and Three Bonds. Effects of Lone-pair Orientation, of Dihedral Angles, and of Protonation

1972 ◽  
Vol 50 (18) ◽  
pp. 2989-3008 ◽  
Author(s):  
R. Wasylishen ◽  
T. Schaffer
Keyword(s):  
Molecular Orbital ◽  
Lone Pair ◽  
Proton Spin ◽  
Coupling Constants ◽  
Spin Coupling ◽  
Phosphorus Compounds ◽  
Molecular Orbital Calculations ◽  
Orbital Theory ◽  
Proton Coupling ◽  
Nitrogen Lone Pair

Molecular orbital theory at the INDO level of approximation is used to calculate the Fermi contact contribution to two-bond and three-bond nitrogen–proton coupling constants for a wide variety of compounds. The dependence of calculated N,H coupling constants upon the spatial orientation of the nitrogen lone-pair is examined for selected molecules. For both saturated and unsaturated compounds the calculated 2J(15N,H) is large and negative when the lone-pair is oriented cis to the proton, and is small and of either sign when the lone-pair lies trans to the proton. Calculated 3J(N,H) depends both on the orientation of the nitrogen lone-pair and on the HCCN dihedral angle. Computed 2J(N,H) and 3J(N,H) generally follow the experimentally known substituent and structural effects. It is suggested that observed phosphorus–proton coupling constants in tervalent phosphorus compounds are dependent on lone-pair orientation in a manner analogous to the corresponding nitrogen–proton coupling constants. The influence of the nitrogen lone-pair orientation on geminal proton–proton coupling constants in methylamine is computed and compared with experiment. Calculated barriers to pyramidal inversion and methyl group rotation are in reasonable agreement with available experimental data.

The Photoelectron Spectra of the N-Chloro and N-Bromo Derivatives of Dimethylamine

1979 ◽  
Vol 32 (4) ◽  
pp. 719 ◽  
Author(s):  
F Carnovale ◽  
T Gan ◽  
JB Peel
Keyword(s):  
Energy Range ◽  
Molecular Orbital ◽  
Ionization Energy ◽  
Lone Pair ◽  
Photoelectron Spectra ◽  
Molecular Orbital Calculations ◽  
Ionization Energies ◽  
Resonance Effects ◽  
Derivatives Of ◽  
Lone Pair Interactions

The He I and He II spectra obtained for chlorodimethylamine (CH3)2NCl, and bromodimethylamine (CH3)2NBr, complete the study of the N-chloro and N-bromo derivatives of the small amines. The valence photoelectron spectra are interpreted with the aid of SPINDO molecular orbital calculations. Trends in the observed ionization energies for both series of small halo amines are described in terms of variations in inductive and resonance effects, the latter particularly concerning the nN/nx lone-pair interactions observed in the low ionization energy range.

Amino and cyano N atoms in competitive situations: which is the best hydrogen-bond acceptor? A crystallographic database investigation

2001 ◽  
Vol 57 (6) ◽  
pp. 850-858 ◽  
Author(s):  
Nahossé Ziao ◽  
Jérôme Graton ◽  
Christian Laurence ◽  
Jean-Yves Le Questel
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonding ◽  
Hydrogen Bonds ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Amino Nitrogen ◽  
Lone Pair ◽  
Molecular Surface ◽  
Molecular Orbital Calculations ◽  
Hydrogen Bond Acceptor

The relative hydrogen-bond acceptor abilities of amino and cyano N atoms have been investigated using data retrieved from the Cambridge Structural Database and via ab initio molecular orbital calculations. Surveys of the CSD for hydrogen bonds between HX (X = N, O) donors, N—T—C≡N (push–pull nitriles) and N—(Csp 3) n —C≡N molecular fragments  show that the hydrogen bonds are more abundant on the nitrile than on the amino nitrogen. In the push–pull family, in which T is a transmitter of resonance effects, the hydrogen-bonding ability of the cyano nitrogen is increased by conjugative interactions between the lone pair of the amino substituent and the C≡N group: a clear example of resonance-assisted hydrogen bonding. The strength of the hydrogen-bonds on the cyano nitrogen in this family follows the experimental order of hydrogen-bond basicity, as observed in solution through the pK HB scale. The number of hydrogen bonds established on the amino nitrogen is greater for aliphatic aminonitriles N—(Csp 3) n —C≡N, but remains low. This behaviour reflects the greater sensitivity of the amino nitrogen to steric hindrance and the electron-withdrawing inductive effect compared with the cyano nitrogen. Ab initio molecular orbital calculations (B3LYP/6-31+G** level) of electrostatic potentials on the molecular surface around each nitrogen confirm the experimental observations.

Hydrogen-Bond Acceptor Properties of Nitro-O Atoms: A Combined Crystallographic Database and Ab Initio Molecular Orbital Study

1997 ◽  
Vol 53 (6) ◽  
pp. 1017-1024 ◽  
Author(s):  
F. H. Allen ◽  
C. A. Baalham ◽  
J. P. M. Lommerse ◽  
P. R. Raithby ◽  
E. Sparr
Keyword(s):  
Hydrogen Bond ◽  
Hydrogen Bonds ◽  
Ab Initio ◽  
Molecular Orbital ◽  
Lone Pair ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Hydrogen Bond Energy ◽  
Hydrogen Bond Acceptor ◽  
Model Dimer

Crystallographic data for 620 C—nitro-O...H—N,O hydrogen bonds, involving 560 unique H atoms, have been investigated to the van der Waals limit of 2.62 Å. The overall mean nitro-O...H bond length is 2.30 (1) Å, which is much longer (weaker) than comparable hydrogen bonds involving >C=O acceptors in ketones, carboxylic acids and amides. The donor hydrogen prefers to approach the nitro-O atoms in the C—NO2 plane and there is an approximate 3:2 preference for hydrogen approach between the two nitro-O atoms, rather than between the C and O substituents. However, hydrogen approach between the two O acceptors is usually strongly asymmetric, the H atom being more closely associated with one of the O atoms: only 60 H atoms have both O...H distances \leq 2.62 Å. The approach of hydrogen along putative O-atom lone-pair directions is clearly observed. Ab-initio-based molecular orbital calculations (6-31G** basis set level), using intermolecular perturbation theory (IMPT) applied to the nitromethane–methanol model dimer, agree with the experimental observations. IMPT calculations yield an attractive hydrogen-bond energy of ca −15 kJ mol−1, about half as strong as the >C=O...H bonds noted above.

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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