Molecular Orbital Studies of Hydrogen Bonds: Dimeric H2O with the Slater Minimal Basis Set

1970 ◽  
Vol 52 (3) ◽  
pp. 1301-1306 ◽  
Author(s):  
Keiji Morokuma ◽  
Jeremy R. Winick
Keyword(s):  
Hydrogen Bonds ◽  
Molecular Orbital ◽  
Basis Set ◽  
Minimal Basis

scholarly journals Crystal Structure, Hirshfeld Surface and Frontier Molecular Orbital Analyses of N-[2-(trifluoromethyl)phenyl]succinamic Acid

2020 ◽  
Vol 32 (12) ◽  
pp. 3179-3185
Author(s):  
P.A. Suchetan ◽  
S. Naveen ◽  
N.K. Lokanath ◽  
P. Krishna Murthy ◽  
M.V. Deepa Urs
Keyword(s):  
Hydrogen Bonds ◽  
Molecular Orbital ◽  
Density Functional ◽  
Hirshfeld Surface ◽  
Basis Set ◽  
Frontier Molecular Orbital ◽  
Reactivity Descriptors ◽  
Succinamic Acid ◽  
Highest Occupied Molecular Orbital ◽  
Lowest Unoccupied Molecular Orbital

The ortho-CF3 substituent and the N-H bond are in syn-conformation in N-[2-(trifluoromethyl)phenyl]succinamic acid. In amide and acid functionalities, the carbonyl groups are directed in opposite directions to each other and their related-CH2 groups. syn-Conformation is observed for the acid functionality, where the carbonyl C=O and hydroxyl O-H bonds are directed in the same direction. Three planar fragments comprise of the molecule: aromatic ring (A), core portion -Carm-N(H)-C(=O)-C(H2)-C(H2)(B) and -C(H2)-C(=O)-OH(C). The dihedral angle between a pair of fragments being 48.6(4)º (A and B), 81.6 (4)º (B and C) and 70.5 (5)º (A and C). N-H•••O hydrogen bonds bind the molecules forming C(4) chains in the crystal, and the neighbouring anti-parallel chains are bound by O-H•••O hydrogen bonds resulting in a chair shaped ribbon of one-dimensional nature. The Hirshfeld surface study was carried out, including fingerprint plots. Studies have shown that the interactions with O•••H/H•••O (27.4%), H•••H (27.3%) and H•••F/F•••H (20.2%) substantially added to the surface. Theoretically, the highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO) and various global reactivity descriptors were also computed by the density functional theory (DFT/B3LYP) approach with a 6-311G(d, p) basis set in the ground state on the geometrically optimized structure in the gas phase.

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.

An ab initio Molecular Orbital Study of Bonding in Fluorocarbonium Ions

1971 ◽  
Vol 49 (22) ◽  
pp. 3708-3713 ◽  
Author(s):  
N. C. Baird ◽  
R. K. Datta
Keyword(s):  
Ab Initio ◽  
Molecular Orbital ◽  
Basis Set ◽  
Molecular Orbital Calculations ◽  
Minimal Basis ◽  
Fluorine Substitution ◽  
Abstraction Reaction ◽  
Carbonium Ions ◽  
Hydride Abstraction ◽  
Resonance Stabilization

Ab initio molecular orbital calculations are reported for the series of carbonium ions (CH3)+, (FCH2)+, and (F2CH)+ and for their neutral molecule counterparts CH4, CH3F, and CH2F2. The energies and wavefunctions for the carbonium ions have been calculated both with and without including the carbon 2pπ orbital in the minimal basis set in order to unravel the inductive destabilization and resonance stabilization due to fluorine substitution. The increase in bonding energy with multiple fluorine substitution is less than linear, due primarily to nonadditivity in the dative carbon–fluorine π bonding. The "saturation" effect noted previously for the hydride abstraction reaction enthalpies is shown to be due primarily to stability effects in the neutral molecules themselves rather than to energetic effects of the carbonium ions.

Single-centre molecular orbital calculations on third row hydrides - SeH2 and HBr

1975 ◽  
Vol 28 (5) ◽  
pp. 927 ◽  
Author(s):  
RGAR Maclagan
Keyword(s):  
Molecular Orbital ◽  
Photoelectron Spectroscopy ◽  
Basis Set ◽  
Basis Sets ◽  
Molecular Orbital Calculations ◽  
Single Centre ◽  
Minimal Basis ◽  
Heavy Atoms ◽  
Orbital Energies ◽  
Orbital Exponents

Single-centre molecular orbital calculations are reported for SeH2, and HBr using basis sets extending up to 5d orbitals centred on the heavy atoms. The choice of orbitals to be used in extending the basis set and the optimum values for orbital exponents are discussed. Orbital energies comparable with minimal basis set multicentre calculations are obtained for SeH2. The orbital energies are compared with those obtained experimentally by photoelectron spectroscopy. The results suggest that the single-centre method is worthy of consideration when studying the hydrides of the heavier elements.

Structures of four o-nitrobenzonitriles

1996 ◽  
Vol 52 (2) ◽  
pp. 344-351 ◽  
Author(s):  
D. Britton ◽  
C. J. Cramer
Keyword(s):  
Hydrogen Bonds ◽  
Molecular Orbital ◽  
Natural Bond Orbital ◽  
Basis Set ◽  
Nucleophilic Attack ◽  
Molecular Orbital Calculations ◽  
Hartree Fock ◽  
Intramolecular Distance ◽  
Delocalization Energy ◽  
Orbital Analysis

The crystal structures of 6-methyl- (I), 6-chloro- (II) and 5-chloro-2-nitrobenzonitrile (III), as well as 2,6-dinitrobenzonitrile (IV), have been determined. (I), orthorhombic, Pbca, a = 9.969 (2), b = 14.728 (4), c = 10.179 (3) Å, T = 180 K; (II), orthorhombic, Pbca, a = 9.469 (5), b = 14.752 (7), c = 10.859 (5) Å, T = 297 K; (III), monoclinic, P21/n, a = 7.889 (2), b = 15.064 (12), c = 7.311 (4) Å, β = 118.22 (3)°, T = 189 K; (IV), orthorhombic, Pbcn, a = 13.081 (6), b = 9.027 (4), c = 6.545 (3) Å, T = 297 K. In (I)–(III) there is a short intramolecular distance [I 2.552 (4), II 2.579 (3), III 2.599 (2) Å] between one of the nitro O atoms and the adjacent nitrile C atom. These short distances plus the accompanying molecular distortions are taken as indications of incipient nucleophilic attack of the O atoms on the electrophilic nitrile C atom. Molecular orbital calculations at the Hartree–Fock level using the 6-31G* basis set support this interpretation; natural bond-orbital analysis indicates an n O1 → π*CN delocalization energy of 10–15 kJ mol−1 for (I), (II) and (III). In (III) and (IV) the molecules pack in sheets, apparently driven by two C—H...O hydrogen bonds and a CN...Cl interaction in (III) and two C—H...O and one C—H...N hydrogen bonds in (IV).

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.

scholarly journals Pentagon functions for scattering of five massless particles

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
D. Chicherin ◽  
V. Sotnikov
Keyword(s):  
Phase Space ◽  
Numerical Evaluation ◽  
Public Library ◽  
Basis Set ◽  
Particle Scattering ◽  
Minimal Basis ◽  
Feynman Integrals ◽  
Analytic Expressions ◽  
Transcendental Functions ◽  
Branch Cuts

Abstract We complete the analytic calculation of the full set of two-loop Feynman integrals required for computation of massless five-particle scattering amplitudes. We employ the method of canonical differential equations to construct a minimal basis set of transcendental functions, pentagon functions, which is sufficient to express all planar and nonplanar massless five-point two-loop Feynman integrals in the whole physical phase space. We find analytic expressions for pentagon functions which are manifestly free of unphysical branch cuts. We present a public library for numerical evaluation of pentagon functions suitable for immediate phenomenological applications.

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