Correlations of chemical shifts of saturated carbon atoms that have a directly bonded substituent

The dependence of the chemical shifts, δ, of saturated carbon atoms upon the nature of the directly bonded substituent is attributed to three factors (1) electronegativity E, (2) field effect, W, and (3) heavy atom ettect, Q. Ten series of compounds (five aliphatic and five cyclic) have been correlated with the equation δ = aE + W + Q+ c where a and c are constants.     

On the splitting of ν(OH) k = 0 phonons and band-width in hydrogen bonded organic solids: α-naphthol

α-naphthol crystallizes with the same type of hydrogen bonded chain like planar zig-zag structure as other XH…X systems (X = F, Cl, Br, and sometimes O). The intramolecular k = 0 splitting for ν(OH) motions of α-naphthol has been clearly observed in the infrared spectrum with polarized light on iso-oriented small single crystals. It is found that the observed intramolecular ν(XH) splitting or the corresponding f_XH/XH nearest neighbour quadratic force constants across the hydrogen bond can be correlated with the electronegativity of the X atom.     

Electronegativity through the energy function

The modern idea of electronegativity based on the E(q) function and the traditional chemical electronegativity are brought together in one self-contained expression. The electronegativity of a molecule is confronted with the in situ electronegativities of the component atoms.     

Functionally substituted arylcopper compounds; crystal structure of the copper bromide complex of [2-(4,4-dimethyl-2-oxazoline)-4-methylphenylcopper]

Arylcopper compounds containing a reactive oxazoline substituent in the ortho position to the CuC bond were synthesized. They react with CuBr to form complexes, and the structure of one of these, [Cu₆(oxl)₄Br₂] (oxl = 4,4-dimethyl-2-oxazoline-4-methylphenyl) was determined by X-ray diffraction. The six copper atoms form a distorded octahedron with four two-electron, three-center bonded bridging aryl groups and two bridging bromine atoms. The aryloxazoline substituent is coordinated via the ipso carbon to two copper atoms, and the imine-N atom is bonded to a third copper atom.     

Electronegativities of elements in covalent crystals

A new electronegativity table of elements in covalent crystals with different bonding electrons and the most common coordination numbers is suggested on the basis of covalent potentials of atoms in crystals. For a given element, the electronegativity increases with increasing number of bonding electrons and decreases with increasing coordination number. Particularly, the ionicity of a covalent bond in different environments can be well-reflected by current electronegativity values; that is, the ionicity of chemical bonds increases as the coordination number of the bonded atoms increases. We show that this electronegativity scale can be successfully applied to predict the hardness of covalent and polar covalent crystals, which will be very useful for studying various chemical and physical properties of covalent materials.     

Crystal and molecular structure of bis[tetracarbonyldiphenylphosphidomanganese(0)]

The crystal structure of bis[tetracarbonyldiphenylphosphidomanganese(0)] has been determined by an X-ray diffraction study. The complex crystallizes in the monoclinic space group P2₁/n with four molecules in a unit cell of dimensions, a 15.714(4), b 16.446(5), c 12.016(4) Å, and β 101.25(2)°. The molecule has approximately centrosymmetric bi-octahedral D_2h structure. Each manganese atom is bonded to two phosphorus atoms of μ-diphenylphosphide groups and four carbonyl carbon atoms. The separation of the manganese atoms is 3.690(1) Å.     

Chemistry and electronegativity

This article addresses the chemical aspects of electronegativity: (1) What is its present status in the chemical community? (2) What are the necessary chemical criteria for a quantitative definition? (3) To what extent do contemporary proposals satisfy these criteria? (4) What connection can be made between the traditional free-atom scales and an in situ electronegativity appropriate for a particular atom in a specific molecule or solid? A longstanding special feature of electronegativity has been the seeming inability to measure it in the laboratory and this aspect proves to be a key to its definition. © 1994 John Wiley & Sons, Inc.     

Ab initio calculations, electronegativity equalisation and group electronegativity

A correspondence betweenab initio calculations, the principle of electronegativity equalisation and group electronegativity has been established within the framework of Mulliken population analysis. Using this we have calculated electronegativities of some 37 groups/atoms. These electronegativities show excellent linear correlation with¹ J _CC coupling constants in monosubstituted benzenes and Inamoto’si scale and a satisfactory one with Wells’ group electronegativity data. The correspondence however required a scaling of charge (obtained byab initio calculations) and a proportionality between the electronegativity of the neutral group and its hardness. It is shown that using these electronegativity values it is possible to calculate group charges in molecules where groups under consideration interact with each other through σ bond only.     

Electronegativity estimator built on QTAIM‐based domains of the bond electron density

The electron localization function, natural localized molecular orbitals, and the quantum theory of atoms in molecules have been used all together to analyze the bond electron density (BED) distribution of different hydrogen‐containing compounds through the definition of atomic contributions to the bonding regions. A function, g_AH, obtained from those contributions is analyzed along the second and third periods of the periodic table. It exhibits periodic trends typically assigned to the electronegativity (χ), and it is also sensitive to hybridization variations. This function also shows an interesting S shape with different χ‐scales, Allred–Rochow's being the one exhibiting the best monotonical increase with regard to the BED taken by each atom of the bond. Therefore, we think this χ can be actually related to the BED distribution. © 2014 Wiley Periodicals, Inc.     

A simple model of hydrogen bonding with particular application to trends in hydrogen‐bonded dimers

A simple model has been proposed to explain trends in the computed interaction energy, bond length changes, frequency shifts and infrared intensities for the chlorofluoromethanes CF_nCl_mH, FH and FArH on complexation with the isoelectronic diatomics BF, CO, N₂ and the rare gas atoms Kr, Ar, Ne to form a series of linear or nearly linear hydrogen‐bonded complexes. The dipole moment derivative of the proton donor (with respect to the stretching coordinate) and the chemical hardness of the hydrogen‐bonded atom of the proton acceptor are identified as two useful parameters for rationalizing the changes in some of the molecular properties of the proton donor when the hydrogen bond is formed. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

How the Chalcogen Atom Size Dictates the Hydrogen-Bond Donor Capability of Carboxamides,Thioamides, and Selenoamides

The amino groups of thio- and selenoamides can act as stronger hydrogen-bond donors than of carboxamides, despite the lower electronegativity of S and Se. This phenomenon has been experimentally explored, particularly in organocatalysis, but a sound electronic explanation is lacking. Our quantum chemical investigations show that the NH₂ groups in thio- and selenoamides are more positively charged than in carboxamides. This originates from the larger electronic density flow from the nitrogen lone pair of the NH₂ group towards the lower-lying π*_C=S and π*_C=Se orbitals than to the high-lying π*_C=O orbital. The relative energies of the π* orbitals result from the overlap between the chalcogen np and carbon 2p atomic orbitals, which is set by the carbon-chalcogen equilibrium distance, a consequence of the Pauli repulsion between the two bonded atoms. Thus, neither the electronegativity nor the often-suggested polarizability but the steric size of the chalcogen atom determines the amide's hydrogen-bond donor capability.     

Thiacyclobutadiene and thiabenzene: A comparative theoretical analysis

The two title compounds have been investigated theoretically using an ab initio SCF-MO treatment at the minimal STO-3G level. It has been found that in the most stable conformation thiacyclobutadiene has all atoms approximately in the same plane except for the H atom bonded to sulphur (i.e. a pyramidal sulphur). On the other hand, in the most stable conformation of thiabenzene, the sulphur atom not only is pyramidal, but also ~10° out of the plane containing the carbon system. The barriers to pyramidal inversion at the sulphur centres are ~48 and ~56 $\text{kcal}\text{mol}$ for thiacyclobutadiene and thiabenzene, respectively. The properties of these molecules are rationalized by means of Perturbation Molecular Orbital (PMO) theory.     

Electronegativity and chemical hardness of organoelement groups

The experimental approaches to estimation of comparative electronegativity and chemical hardness of organometallic groups have been proposed. Qualitative data on the electronegativity of L _nM groups were obtained from ¹⁹F NMR study of model systems 4‐FC₆H₄QML_n (Q = CC, N(R), O, C(O)O, S), (4‐FC₆H₄)₃ SnML _n and (4‐FC₆H₄)₃SnQML _n (Q = O, S), containing a great variety of different organometallic groups containing transition or heavy main‐group metals. The data on chemical hardness of L _nM groups were obtained from NMR study of distribution of different L _nM groups between hard and soft anions. The following basic results have been obtained. (1) The relative electronegativity and chemical hardness of L _nM groups can change in parallel or not with the electronegativity and hardness of the central metal atom. (2) The substituents in Ar can substantially modify electronegativity and hardness of Ar _nM groups; the influence of Ar groups has an inductive nature; the increase in electron‐donating ability of aryl ligands enhances the hardness of Ar _nM cations. (3) The relative electronegativity and hardness of L _nM groups in L _nMX are invariant and do not depend on X.     

Are the hydrogen bonds involving sulfur bases inverse or anomalous?

The hydrogen‐bonded complexes (HBCs) of H₂S, CH₂S, and CH₄S with H–F (hydrogen fluoride) were studied within the framework of the quantum theory of atoms in molecules at several theoretical levels (HF, B3LYP, MP2, and QCISD) with a wide range of basis sets. According to the integrated atomic populations obtained at correlated levels, the interacting hydrogen of the acid gains charge upon complexation, in sharp contrast to the conventional picture of hydrogen bonding, whereas the HF method yields a small loss of charge. The study of several H_nA…H_mD HBCs of hydrides, where A is the hydrogen‐acceptor atom and D is the atom bonded to the hydrogen donor, reveals this behavior is followed when the electronegativity of D significantly exceeds that of A. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

A molecular orbital study comparing the effects of heteroatom substitution in trans-1,3-butadiene,all-trans-1,3,5-hexatriene,and benzene

To gain more understanding of the nature of the perturbation that results from heteroatom substitution in conjugated polyenes and in an aromatic ring environment, we have carried out calculations ontrans-H₂C=X(H)-CH=CH₂, all-trans-H₂C=CH-X(H)=CH-CH=CH₂, and with X = C, N, Si, and P, using the 6-31G^*(5D) basis set with full geometry optimization. Linear relationships are found between (a) the C-X and C-C bond lengths, (b) the total overlap population in the C-C, C-N, C-Si, and C-P bonds and the bond length, and (c) the total atomic charge on the N, Si, and P atoms and the corresponding C atom in the various structures, and the electronegativity of N, Si, P and C. Whereas Si is more strongly bonded in the diene and triene compared to the aromatic ring, P, like N, appears to be bonded equally well in all three structural environments.     

The molecular structure of chlorothiomethoxymethyl-bis(triphenylphosphine)palladium(II) methylenechloride solvate at −160°C

The precise molecular structure of [PdCl(CH₂SCH₃)(PPh₃)₂] has been determined from three-dimensional X-ray diffraction data collected at ?160°C. The CH₂Cl₂ solvated crystal ([PdCl(CH₂SCH₃)(PPh₃)₂ · CH₂Cl₂]) belongs to the monoclinic system, space group P2₁/n, with four formula units in a cell of dimensions: a 14.973(3), b 15.333(3), c 17.377(3) Å and β 115.77(1)° at ?160°C. The structure was solved by the conventional heavy atom method and refined by the least-squares procedure to R = 0.035 for observed reflections. The geometry around the palladium atom is square-planar. The phosphorus atoms of the two triphenylphosphine ligands are mutually trans. The CH₂SCH₃ group is bonded to the palladium atom only through the PdC σ-bond and the sulfur atom is not bonded to the metal atom (PdC(1) 2.061(3), SC(1) 1.796(3), SC(2) 1.817(5), Pd?S 2.973(1) Å, PdC(1)S 100.64(14)° and C(1)SC(2) 101.28(18)°). The structure is in contrast to that of [PdCl(CH₂SCH₃)(PPh₃)], in which both the carbon and sulfur atoms of the CH₂SCH₃ group are bonded to the palladium atom.