Conformationally induced and conjugatively amplified doubly degenerate uneven sulfuranes

1994 ◽  
Vol 72 (10) ◽  
pp. 2153-2158
Author(s):  
Elizabeth A. Innes ◽  
Imre G. Csizmadia ◽  
Jean-Louis Rivail ◽  
Michel Loos ◽  
Árpád Kucsman
Keyword(s):  
Potential Energy Surfaces ◽  
Valence Electron ◽  
Lone Pair ◽  
Equatorial Position ◽  
Electron Pairs ◽  
Bond Lengths ◽  
The Difference ◽  
Torsional Angles ◽  
Energy Surfaces ◽  
The Ideal

Sulfuranes, containing hypervalent or 10 valence electron central sulfur atoms of the type CH3(H)SCl2 (I), H2N(H)SCl2 (II), HO(H)SCl2 (III), (H2N)2SCl2 (IV), and (HO)2SCl2 (V) have been studied by ab initio MO computations. All sulfuranes exhibited pseudo trigonal bipyramide structure as appropriate 5 valence electron pairs. The two chlorine atoms were in apical positions and the other two ligands were in equatorial position. The fifth electron pair was a lone pair, also located in an equatorial position. The lone pair "pushed away" the S—Cl bonds from the ideal axis of the trigonal bipyramide and therefore the ClSCl bond angle was always less than 180°. With the changing conformations of the equatorial groups the axial bond lengths are varied. Even though the compounds had constitutionally identical S—Cl bonds at certain torsional angles of the equatory ligands the two S—Cl bond lengths became unequal. The difference between the two bond lengths was used as a measure of the extent of unevenness of the sulfurane structures. This led to the creation and annihilation of certain critical points on the conformational Potential Energy Surfaces.

BOND LENGTHS AND BOND ANGLES IN OCTAHEDRAL, TRIGONAL- BIPYRAMIDAL, AND RELATED MOLECULES OF THE NON-TRANSITION ELEMENTS

1961 ◽  
Vol 39 (2) ◽  
pp. 318-323 ◽  
Author(s):  
R. J. Gillespie
Keyword(s):  
Central Atom ◽  
Lone Pair ◽  
Pauli Exclusion Principle ◽  
Exclusion Principle ◽  
Transition Elements ◽  
Electron Pairs ◽  
Bond Angles ◽  
Bond Lengths ◽  
Trigonal Bipyramidal ◽  
The Difference

The stereochemistry of molecules in which there are five or six pairs of electrons in the valency shell of a central atom is discussed in terms of the repulsions that exist between pairs of electrons in the valency shell as a consequence of the operation of the Pauli exclusion principle. An explanation is given for the difference in lengths of the axial and equatorial bonds in molecules such as PCl5 and ClF3 whose structures are based on the trigonal-bipyramidal arrangement of five valency-shell electron pairs. The fact that in molecules with a central atom with a valency shell of six electron pairs, one of which is a lone pair and which have the structure of a square pyramid, the central atom always lies below rather than in, or above, the base of the square pyramid, is also accounted for.

THEORETICAL STUDIES ON THE FORMATION MECHANISM AND STRUCTURE OF PENTAFULVENONE AND AZAFULVENONE

2008 ◽  
Vol 07 (02) ◽  
pp. 233-246 ◽  
Author(s):  
XIU-MEI PAN ◽  
XIU-JUAN JIA ◽  
YING LIU ◽  
HAO SUN ◽  
ZHONG-MIN SU ◽  
...  
Keyword(s):  
Nitrogen Atom ◽  
Potential Energy Surfaces ◽  
Vibrational Mode ◽  
Formation Mechanisms ◽  
Ortho Position ◽  
Elimination Reaction ◽  
Diazo Ketone ◽  
The Difference ◽  
Energy Surfaces ◽  
Mode Assignment

The formation mechanisms of pentafulvenone and azafulvenone were extensively investigated at the B3LYP/6-311++G** level and the potential energy surfaces were drawn out. Ketene pentafulvenone (A) and 3-carbonyl-3H-pyrrole (C) can be formed by eliminating N 2 from the diazo ketone via α elimination reaction and ketene 2-carbonyl-2H-pyrrole (B), 4-carbonyl-4H-imidazole (D), and 2-carbonyl-2H-imidazole (E) were formed by the elimination of water or methanol from pyrrole-2-carboxylic acid (rB) and carboxylate (rD and rE) via β elimination reaction. The structures of these monomers were compared and showed some information about the bond changed characters. The structure investigation indicated that the C = C bond is activated when the nitrogen atom locates in the ortho position of the C = C = O part, and therefore ortho-monomers are more facile to react. The difference of the amount and stability of the corresponding dimers are caused by differing the position and number of nitrogen atom and the variety of the ortho-dimer is complicated. In addition, the infrared spectra of the title species were also analyzed including the vibrational frequencies, IR relative intensities, and vibrational mode assignment.

STEREOCHEMISTRY OF ARSENIC: PART VI. TRI-p-TOLYLARSINE

1963 ◽  
Vol 41 (1) ◽  
pp. 14-17 ◽  
Author(s):  
J. Trotter
Keyword(s):  
Van Der Waals ◽  
Lone Pair ◽  
Unit Cell ◽  
Van Der Waals Interactions ◽  
Ideal Model ◽  
Cell Axis ◽  
Bond Lengths ◽  
Cell Dimensions ◽  
Intermolecular Contacts ◽  
The Ideal

Crystals of tri-p-tolylarsine are rhombohedral, with cell dimensions a = 9.84 Å, α = 80° 2′, and space group [Formula: see text]. There are two molecules in the unit cell, and hence the molecule has symmetry C3. The structure has been determined from a projection along the rhombohedral cell axis, and the bond lengths and valency angles are given. In comparison with an ideal model having maximum interaction between the arsenic lone pair and the aromatic π-electrons, each ring is rotated about its As—C bond by 36°, the three rotations being in the same sense. These displacements increase overcrowded distances in the ideal model to about the normal van der Waals separations, the closest intramolecular contacts between p-tolyl groups being [Formula: see text] and [Formula: see text]. All the intermolecular contacts correspond to van der Waals interactions.

Photoelektronenspektren und Moleküleigenschaften, LXIV. Dimethyldiselenid — ein Beispiel für die Wechselwirkung zwischen benachbarten Elektronenpaaren / Photoelectron Spectra and Molecular Properties, LXIV. Dimethyldiselenide - an Example for the Interaction between Adjacent Electron Pairs

1976 ◽  
Vol 31 (12) ◽  
pp. 1616-1620 ◽  
Author(s):  
Galina Tschmutowa ◽  
Hans Bock
Keyword(s):  
General Model ◽  
Photoelectron Spectrum ◽  
Valence Electron ◽  
Lone Pair ◽  
Dimethyl Disulfide ◽  
Molecular Properties ◽  
Photoelectron Spectra ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Electron Pairs

The well-resolved helium(I) photoelectron spectrum of H3C-Se—Se-CH3 exhibits distinct bands corresponding to 11 of the total 13 valence electron ionizations. The unequivocal assignment is supported by EHMO calculations including spin/orbit coupling. The two selenium lone pair ionizations differ by 0.23 eV; a split observed also for dimethyl disulfide and discussed within a general model for interactions between adjacent lone pairs.

INVESTIGATION OF THE CONTRIBUTION FOR THE NONCOLLINEAR CHANNEL OF THE F(2P3/2,2P1/2) + H2/D2 REACTIONS ON FOUR DIABATIC POTENTIAL ENERGY SURFACES

2012 ◽  
Vol 11 (03) ◽  
pp. 561-571 ◽  
Author(s):  
TING-XIAN XIE
Keyword(s):  
Potential Energy ◽  
Barrier Height ◽  
Cross Sections ◽  
Rate Constants ◽  
Potential Energy Surfaces ◽  
Collision Energy ◽  
Higher Temperature ◽  
The Difference ◽  
Lower Temperature ◽  
Energy Surfaces

We performed the nonadiabatic time-dependent wave packet calculation on the four diabatic potential energy surfaces, which have the different barrier height, to investigate the contribution of the noncollinear channel for the F (2P) + H2/D2 (v = j = 0) reactions. The reaction probabilities, integral cross-sections, and rate constants are presented. The results indicate that the probabilities as the function of the collision energy have an obvious translation. The reactive activity of the reactions comes from the noncollinear reactive channel. The bent barrier height would decrease the reactive activity. The integral cross-sections are in the order of AWS < LWA-5 < LWA-78 ≈ MASW, which is opposite to that of the bent barrier height. At the lower temperature, the difference of the rate constants is unambiguous. As the temperature increases, the difference reduces. At the higher temperature, the rate constants computed on the four potential energy surfaces are close.

Ab initio 3-21 G Calculations of Push-Pull Interactions of Substituents at Imino-Nitrogen in Formamidines. Non-Equivalence of NO-Bonds of the Nitro-Substituent

1992 ◽  
Vol 47 (10) ◽  
pp. 1480-1490 ◽  
Author(s):  
Günter Häfelinger ◽  
Tadeusz Marek Krygowski ◽  
Frank K. H. Kuske
Keyword(s):  
Charge Density ◽  
Ab Initio ◽  
Amino Nitrogen ◽  
Lone Pair ◽  
Molecular Structures ◽  
Electron Charge Density ◽  
Imino Nitrogen ◽  
Bond Lengths ◽  
Mechanism Of Interaction ◽  
The Difference

Full ab initio 3-21 G optimization of molecular structures of twelve planar formamidines substituted by X in Ε-configuration at imino nitrogen (N2) (X = H, CH3, NH2, C6H5, OH, F, CHO, CN, BH2, NO (four isomers), NO2 (planar and perpendicular conformations), and CH2+) yielded the following conclusions: (1) as was found earlier experimentally, an increase of the shorter CN2 bond lengths is associated linearly with a decrease of the longer CN1 bond; (2) the difference of both CN distances (Δ CN) is related linearly to the Mulliken π-electron charge density at amino nitrogen (N1); (3) a decrease of Mulliken π-charge density (Δ qπ) at N1 is linearly related to a corresponding increase of Δ qπ at N2. The scatter and a slope of –0.54 indicate a mixed mechanism of interaction between NH2 and the substituents at amino nitrogen composed of n-π-conjugation and through conjugation; (4) an increase of σ-charge density at H2 is correlated with an increase of N1 – H2 bond lengths. As a result of interaction between the lone pair at N2 and the cis-bond of the nitro substituent this bond is calculated to be significantly shorter than the other one by 0.042 A. The same effect is calculated for the E-isomer of C-nitro substituted formamidine (Δ = 0.037 A) in contrast to the corresponding Z-isomer (Δ = 0.004 Å). A selection of experimental X-ray determinations of nitro-substituted compounds confirm this effect.

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