# Peter Politzer's research while affiliated with University of New Orleans and other places

## Publications (556)

Article
We have shown in the past that the electrostatic potential at the nucleus of a given atom A is relatively insensitive to that atom’s molecular environment. However, the separate nuclear and electronic contributions to it can be quite different. For a free atom, the electrostatic potential at the nucleus is due entirely to its electrons. If this wer...
Article
There continues to be confusion concerning the concept of electronegativity. Pauling's original approach, focusing upon an atom in a molecule, continues to be widely invoked. There has also been a more recent tendency to view electronegativity as the negative of the chemical potential and to extend it to molecules. However this leads to results tha...
Article
Full-text available
The power of the Hellmann–Feynman theorem is primarily conceptual. It provides insight and understanding of molecular properties and behavior. In this overview, we discuss several examples of concepts coming out of the theorem. (1) It shows that the forces exerted upon the nuclei in a molecule, which hold the molecule together, are purely Coulombic...
Article
We address the long-standing controversy as to the physical origin of covalent bonding, whether it involves a lowering of the potential energy or a lowering of the kinetic energy. We conclude that both of these do occur and contribute to the formation of the bond. The analysis is in terms of the virial theorem and the variations in the potential en...
Chapter
A major problem in the area of explosives is combining a high level of detonation performance with an acceptably low level of sensitivity to accidental detonation. We discuss three molecular and crystalline factors that are believed to be fundamentally related to impact sensitivity. We emphasize that these factors are not claimed to correlate with...
Article
A high priority in designing and evaluating proposed explosives is to minimize sensitivity, i.e., vulnerability to unintended detonation due to an accidental stimulus, such as impact. In order to establish a capability for predicting impact sensitivity, there have been numerous attempts to correlate it with some molecular or crystal property or pro...
Chapter
The most extensive use of computed molecular electrostatic potentials has been in relation to reactive behavior. Nucleophilic portions of each molecule would interact favorably with the regions of most positive electrostatic potential on the other, especially the surface local maxima. Molecular electrostatic potentials have been extensively used in...
Article
It follows from the Schrödinger equation that the forces operating within molecules and molecular complexes are Coulombic, which necessarily entails both electrostatics and polarization. A common and important class of molecular complexes is due to π-holes. These are molecular regions of low electronic density that are perpendicular to planar porti...
Article
Full-text available
Since the nuclei in a molecule are treated as stationary, it is perhaps natural that interpretations of molecular properties and reactivity have focused primarily upon the electronic density distribution. The role of the nuclei has generally received little explicit consideration. Our objective has been to at least partially redress this imbalance...
Article
We use the term "counter‐intuitive" to describe an intermolecular interaction in which the electrostatic potentials of the interacting regions of the ground‐state molecules have the same sign, both positive or both negative. In the present work, we consider counter‐intuitive halogen bonding with nitrogen bases, in which both the halogen σ‐hole and...
Article
Full-text available
A widely used criterion for the existence of a noncovalent interaction is that the interatomic separation be less than the sum of the van der Waals radii of the respective atoms. However, this criterion should not be applied rigidly, but rather with considerable caution and flexibility, for several reasons. First, there is considerable uncertainty...
Article
The site of the greatest electronic density of the highest-occupied molecular orbital (HOMO) is often taken to be the location of the most energetic electrons in a molecule, and thus the most likely site for reaction with an electrophile. However we show, by reference to the average local ionization energy on a molecular surface, that the HOMO alon...
Article
Fourteen oxatriazoles have been investigated computationally as potential energetic compounds. They include the two isomeric parent compounds, their amino and nitro derivatives, four N‐oxides and four amino‐N‐oxides. Densities and solid state heats of formation were calculated for all of these compounds, and used to determine their detonation veloc...
Article
Full-text available
The electrostatic potential at the nucleus of an atom, whether in the free state or in a molecule, is qualitatively a characteristic property of the atom. It changes remarkably little from one molecular environment to another. The energies of atoms and molecules can be expressed both rigorously and approximately in terms of the electrostatic potent...
Article
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Experimental and theoretical studies of fluoro-, chloro-, and bromo-substituted derivatives of barbituric acid and indandione show that imide protons form short hydrogen bonds and bromine or, to a lesser extent, chlorine atoms form halogen bonds. The imide nitrogen atoms act as effective pnictogen bond donors, while C(sp²) and C(sp³) atoms act as t...
Article
Following a brief survey of some anomalous properties of fluorine, both as an atom and as a constituent of molecules, we computed electrostatic potentials on molecular surfaces to examine some noncovalent interactions of fluorinated compounds. We demonstrate that the relative rarity and weakness of organic fluorine acting as a hydrogen bond accepto...
Article
The solubility of a compound is one of its most important properties. Here, regression relationships are presented for solubilities of a series of gases in water and in four organic solvents, treating each solvent separately. The solubilities are related to the Coulombic intermolecular interactions arising from the intrinsic polarities of the solut...
Article
Molecular electrostatic potentials, in conjunction with polarization, provide the key to understanding hydrogen bonding. As required by the Hellmann–Feynman theorem, hydrogen bonding is a Coulombic interaction between (a) a positive electrostatic potential associated with a region of lower electronic density on the hydrogen (a σ-hole), and (b) a ne...
Article
The energetics of σ‐ and π‐hole interactions can be described very well in terms of electrostatics and polarization, consistent with their Coulombic natures. When both of these components are taken into account, very good correlations with quantum‐chemically computed interaction energies are obtained. If polarization is only minor, as when the inte...
Article
The interactions between a wide variety of molecules having σ-holes or π-holes and several nitrogen bases have been analyzed computationally. The σ- and π-hole atoms span Groups III-VII of the periodic table. The interaction energies range from quite weak, typical of noncovalent bonding, to unusually strong: from -4.6 to -22.0 kcal/mol for the σ-ho...
Article
Full-text available
Even after roughly a century of quantum theory, there is still debate, sometimes rather contentious, as to the nature of the chemical bond—or is it bonds, or is it bonding? In this brief overview, we summarize some of the prominent approaches to this and related issues. A key focus in any interpretation must be satisfying the two requirements that...
Article
Full-text available
Our discussion focuses upon three possible features that a bonded halogen atom may exhibit on its outer side, on the extension of the bond. These are (1) a region of lower electronic density (a σ-hole) accompanied by a positive electrostatic potential with a local maximum, (2) a region of lower electronic density (a σ-hole) accompanied by a negativ...
Article
It was shown by Kamlet and Jacobs that an explosive's detonation velocity D and detonation pressure PD are governed largely by (a) the loading density of the explosive, and (b) a factor ϕ that depends upon the number and masses of gaseous detonation products and the accompanying heat release. For a series of different explosives, we show that the d...
Article
We report a computational study of two series of molecules, one having the Si–O–N linkage and the other with the Si–(CH2)n–N linkage, where n = 1–4. The silicons have various substituents—combinations of H, CH3, F, Cl and CF3. Many of these compounds have been prepared and characterized experimentally. The Si···N distances were found to be relative...
Article
Full-text available
Quantum mechanics, through the Hellmann–Feynman theorem and the Schrödinger equation, show that noncovalent interactions are classically Coulombic in nature, which includes polarization as well as electrostatics. In the great majority of these interactions, the positive electrostatic potentials result from regions of low electronic density. These r...
Chapter
The N‐oxide bond, which will be written as N→O, is formally coordinate covalent, with both electrons being provided by a covalently bonded nitrogen. A more realistic description is that the nitrogen lone pair is polarized toward the oxygen by the electric field of the latter. Our present focus is upon the N‐oxides of polyazoles and polyazines, part...
Article
The term “chemical hardness” refers to the resistance to deformation of the electronic density of a system; the greater this resistance, the “harder” the system. Polarizability, a physical property, is an inverse measure of resistance to deformation and thus should be inversely related to hardness. This is indeed generally accepted. Hardness has be...
Article
Since quantum mechanical calculations do not typically lend themselves to chemical interpretation, analyses of bonding interactions depend largely upon models (the octet rule, resonance theory, charge transfer, etc.). This sometimes leads to a blurring of the distinction between mathematical modelling and physical reality. The issue of polarization...
Article
Our focus is upon a noncovalent molecular complex after its formation. In earlier work, we determined the ‘impenetrable’ volumes of the molecules A and B in a series of bimolecular complexes. In this paper, we investigate the amount and distribution of electronic charge that is excluded from these impenetrable volumes in each complex. We show that...
Article
The Hellmann-Feynman theorem has, with a few exceptions, not been exploited to the degree that it merits. This is due, at least in part, to a widespread failure to recognize that its greatest value may be conceptual rather than numerical, i.e., in achieving insight into molecular properties and behavior. In this brief overview, we shall discuss thr...
Article
It is shown that the interactions of dihalogen molecules XY with halide anions Z‒ to form trihalide anions (XYZ)‒ can be satisfactorily described as Coulombic, involving the σ‐holes on the atoms Y, but only if polarization is taken into account. We have approximated the polarizing effect of the halide anion Z‒ by means of a unit negative point char...
Article
Electronegativity is a very useful concept but it is not a physical observable; it cannot be determined experimentally. Most practicing chemists view it as the electron-attracting power of an atom in a molecule. Various formulations of electronegativity have been proposed on this basis, and predictions made using different formulations generally ag...
Article
In crystals of a benzoselenazole dye, a network of hydrogen bonds with the dye cations locks two iodide anions at a distance allowing for an iodine molecule to be pinned...
Article
Full-text available
Schneider has observed that [1]: “ . . . the chemistry of the last century was largely the chemistry of covalent bonding, whereas that of the present century is more likely to be the chemistry of noncovalent binding.”[...]
Chapter
Polyazoles and polyazines are, respectively, five- and six-membered nitrogen heterocycles. An interesting difference between their geometries is that it is possible in polyazoles (but not in polyazines) to distinguish between formal single and formal double bonds. Our particular focus in this chapter is on those polyazoles and polyazines that featu...
Article
A covalently-bonded atom typically has a region of lower electronic density, a “σ-hole,” on the side of the atom opposite to the bond, along its extension. There is frequently a positive electrostatic potential associated with this region, through which the atom can interact attractively but noncovalently with negative sites. This positive potentia...
Article
σ‐Holes and π‐holes are two types of regions of lower electronic density that are frequently found in molecules. There are often positive electrostatic potentials associated with them, through which the molecule can interact attractively with negative sites to form noncovalent bonds. The Hellmann–Feynman theorem shows that these interactions are Co...
Chapter
After mentioning methods for quantifying detonation performance and sensitivity, we proceed to discuss some factors that govern these properties. To enhance the likelihood of an explosive having high performance in conjunction with low or moderate sensitivity, it should have (a) a high density, and (b) a large number of moles of gaseous detonation...
Article
σ-Holes and π-holes are regions of molecules with electronic densities lower than their surroundings. There are often positive electrostatic potentials associated with them. Through these potentials, the molecule can interact attractively with negative sites, such as lone pairs, π electrons, and anions. Such noncovalent interactions, "σ-hole bondin...
Article
Full-text available
The polyazoles have five-membered heterocyclic rings with N/C ratios of at least 2/3. Their high nitrogen contents result in relatively high crystal densities and large positive heats of formation, features that make them attractive as frameworks for energetic materials. However the presence of linked nitrogens (catenation) is accompanied by reduce...
Article
We propose to characterise the “impenetrable” volumes of molecules A and B in a complex A---B by finding that contour of its electronic density that separates the molecular surfaces of A and B but leaves them almost touching. The volume of the complex within that contour is always less than within the 0.001 au contour. The percent difference measur...
Article
Close contacts, defined as interatomic separations less than the sum of the respective van der Waals radii, are commonly invoked to identify attractive nonbonded interactions in crystal lattices. While this is often effective, it can also be misleading because (a) there are significant uncertainties associated with van der Waals radii, and (b) it m...
Article
Full-text available
After a brief discussion of the σ-hole concept and the significance of molecular electrostatic potentials in noncovalent interactions, we draw attention to some common misconceptions that are encountered in that context: (1) Since the electrostatic potential reflects the contributions of both the nuclei and the electrons, it cannot be assumed that...
Article
Single crystal X-ray analysis shows that intermolecular C–S∙∙∙F chalcogen bonds are by far the shortest contacts in the crystal structure of 2,2,4,4-tetrafluoro-1,3-dithietane. Analysis of the molecular surface electrostatic potentials indicates that these contatcs result from the attraction between the negative potentials of fluorines and the posi...
Article
Full-text available
Halogen bonds have been identified in a series of ionic compounds involving bromonium and iodonium cations and several different anions, some also containing hypervalent atoms. The hypervalent bromine and iodine atoms in the examined compounds are found to have positive σ-holes on the extensions of their covalent bonds, while the hypervalent atoms...
Article
Increasing the nitrogen/carbon ratios in the molecular frameworks of C,H,N,O explosives has attracted considerable attention because it tends to result in more positive heats of formation and often greater densities. In conjunction with this, there has been a growing interest in N-oxide linkages, N⁺ → O⁻, as another source of oxygen in these compou...
Article
We have investigated the relevance for ionic explosive sensitivity of three factors that have been demonstrated to be related to the sensitivities of molecular explosives. These are (1) the maximum available heat of detonation, (2) the amount of free space per molecule (or per formula unit) in the crystal lattice and (3) specific features of the el...
Article
Some general guidelines and specific molecular/crystalline features for promoting a high level of detonation performance in conjunction with low sensitivity are proposed. A key point is that a large detonation heat release should be avoided; it is undesirable with respect to sensitivity and it is not required in terms of performance.
Article
We have computed the most positive and most negative values of the electrostatic potentials on the surfaces of a series of molecules, some of which contain atoms from the second and third rows of Groups IV, VI and VII. Three different methods were used – Hartree-Fock and the density functional B3LYP and M06-2X – in conjunction with numerous basis s...
Article
The hydrogen bonding of non-coordinated water molecules to each other and to water molecules that are coordinated to metal ion complexes has been investigated by means of a search of the Cambridge Structural Database (CSD) and through quantum chemical calculations. Among the metal complexes were both tetrahedral and octahedral ones, charged and neu...
Article
Full-text available
We have investigated possible relationships between four crystal properties: experimental densities and computed intrinsic molecular volumes, packing coefficients and amounts of free space per molecule in the crystal lattices. Our focus was upon C-, H-, N-, O-containing explosive compounds. The objectives were to gain some insight into how densitie...
Article
Full-text available
The computed electrostatic potentials on C,H,N,O molecular solids and nitrogen-rich C,H,N,O salts are used in analyzing and comparing intralattice attractive forces and crystal densities in these two categories of compounds. Nitrogen-rich C,H,N,O salts are not an assured path to high densities. To increase the likelihood of high densities, small ca...
Article
We demonstrate that a large heat of detonation is undesirable from the standpoint of the impact sensitivity of an explosive and also unnecessary from the standpoints of its detonation velocity and detonation pressure. High values of the latter properties can be achieved even with a moderate heat of detonation, and this in turn enhances the likeliho...
Article
The important role that electrostatic potentials computed on molecular surfaces can have in designing new materials via co-crystallization is discussed and illustrated. The locally most positive and most negative values of the surface electrostatic potential identify and rank sites for hydrogen bonding (complementing Etter's rules), halogen bonding...
Article
The term “σ-hole” refers to a region of diminished electronic density along the extension of a covalent single bond to a hydrogen or an atom of Groups IV—VII. This region often has a positive electrostatic potential through which the atom can interact attractively with a negative site (such as a lone pair of a Lewis base, π electrons or an anion) t...
Article
The Hellmann-Feynman theorem provides a straightforward interpretation of noncovalent bonding in terms of Coulombic interactions, which encompass polarization (and accordingly include dispersion). Exchange, Pauli repulsion, orbitals, etc., are part of the mathematics of obtaining the system's wave function and subsequently its electronic density. T...
Article
We discuss three molecular/crystalline properties that we believe to be among the factors that influence the impact/shock sensitivities of energetic materials (i.e., their vulnerabilities to unintended detonation due to impact or shock). These properties are (a) the anomalously strong positive electrostatic potentials in the central regions of thei...
Chapter
In designing new explosives, a key goal is to achieve an optimum balance between two inherently contradictory objectives: a high level of detonation performance and low sensitivity to accidental initiation of detonation. There appears to be a reasonably good understanding of the determinants of detonation performance, and there are procedures avail...
Article
The anisotropic electronic densities of covalently-bonded Group IV-VII atoms frequently give rise to regions of positive electrostatic potential on the extensions of single covalent bonds to these atoms. Through such positive "σ-holes," the atoms can interact attractively and highly directionally with negative sites such as the lone pairs of Lewis...
Article
The Hellmann–Feynman theorem assures us that the forces felt by the nuclei in a molecule or complex are purely classically electrostatic. Nevertheless, it is often claimed (incorrectly) that electrostatic considerations are not sufficient to explain noncovalent interactions. Such assertions arise largely from neglecting the polarization that is inh...
Article
Full-text available
The reaction force F(ξ) is the negative gradient of the potential energy of a chemical process along the intrinsic reaction coordinate ξ. We extend the rigorous concept of F(ξ) to the “activation strain model” of Bickelhaupt et al., to formulate the “strain” force F str(ξ) that retards a reaction and the “interaction” force F int(ξ) that drives it....
Chapter
The average local ionization energy $${\bar{\text{I}}}(\mathbf{r})$$ has the very important practical advantage that its minimum values on molecular surfaces, the $${{{\bar{\text{I}}}}_{\text{S,min}}},$$ can generally identify the most reactive sites in a system in a single calculation, that encompasses all possible sites. The \({{{\bar{\text{I}}}}...
Article
A σ-hole is a region of diminished electronic density on the extension of a covalent bond to an atom. This region often exhibits a positive electrostatic potential, which allows attractive noncovalent interactions with negative sites. In this study, we have systematically examined the dependence of σ-hole potentials upon (a) the atom having the σ-h...
Article
There is considerable evidence, which we discuss, indicating that compressibility and available free space in the crystal lattice are among the factors that govern the sensitivity of an explosive compound. Expanding and extending earlier work, we demonstrate, for 25 explosives, that there is an overall general tendency for greater impact sensitivit...
Article
Full-text available
We have computationally compared three Diels-Alder cycloadditions involving cyclopentadiene and substituted ethylenes; one of the reactions is synchronous, while the others are slightly or highly asynchronous. Synchronicity and weak asynchronicity are characterized by the reaction force constant κ(ξ) having just a single minimum in the transition r...
Article
N-oxides feature a coordinate covalent N+→O− bond, in which both electrons formally come from the nitrogen. Such compounds are important in organic and biological chemistry, and increasingly in the area of energetic materials. The N+→O− linkage has the interesting property that it can be either a donor or an acceptor of electronic charge through re...
Article
Full-text available
Covalently-bonded atoms of Groups IV-VII tend to have anisotropic charge distributions, the electronic densities being less on the extensions of the bonds (sigma-holes) than in the intervening regions. These sigma-holes often give rise to positive electrostatic potentials through which the atom can interact attractively and highly directionally wit...
Chapter
The “sensitivity” of an explosive refers to its vulnerability to accidental detonation due to an unintended stimulus, such as impact, shock, and so on. The long-standing objective of diminishing the sensitivities of explosives coincides with one of the goals of green chemistry, that is minimizing the potential for chemical accidents. This involves...
Article
Four sets of rules for predicting the detonation product compositions of explosives have been investigated: the Kamlet-Jacobs, the Kistiakowsky-Wilson, the modified Kistiakowsky-Wilson and the Springall-Roberts. These can result, for a given compound, in significantly differing detonation products and amounts of heat release. However the resulting...
Article
A classical point-charge self-consistent polarization model has been used to investigate the role of polarization in the CF3Cl:OH2 complex. The polarised electron densities of the monomers component are shown to be a good representation of the electron densities of complexes, especially CF3Cl. The point-charge model overestimates the polarization o...
Article
There is considerable interest in polyazine N-oxides as potential frameworks for energetic compounds with relatively high enthalpies of formation and crystal densities. The N+→O− linkages, if appropriately located, may diminish the destabilization associated with nitrogen catenation. We have computationally characterized 40 N-oxides of the isomeric...
Article
Full-text available
Both HCN and HNC are prominent in the interstellar medium and may have significant roles in prebiotic chemistry. Considerable attention has, therefore, been accorded to the HCN ↔ CNH isomerisation, sometimes viewed as a prototypical unimolecular process. However, detailed analysis of the potential energy of the HCN/CNH system along its intrinsic re...
Article
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This recommendation proposes a definition for the term “halogen bond”, which designates a specific subset of the inter- and intramolecular interactions involving a halogen atom in a molecular entity.
Article
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A variety of experimental and computational analyses support the concept that a chemical reaction has a transition region, in which the system changes from distorted states of the reactants to distorted states of the products. The boundaries of this region along the intrinsic reaction coordinate ξ, which includes the traditional transition state, a...
Article
The interaction energies between an argon atom and the dihalogens Br2, BrCl, and BrF have been investigated using frozen core CCSD(T)(fc)/aug-cc-pVQZ calculations as reference values for other levels of theory. The potential-energy hypersurfaces show two types of minima: (1) collinear with the dihalogen bond and (2) in a bridging position. The form...
Article
Halogen bonding in the gas phase is often thermodynamically unstable, because of the loss of entropy incurred when the translational and rotational motions of the free molecules are constrained by the formation of the complex. This produces a large negative TΔS term, which can in many instances dominate ΔH and result in ΔG = ΔH − TΔS > 0. This redu...
Article
A σ-hole bond is a noncovalent interaction between a covalently-bonded atom of Groups IV-VII and a negative site, e.g. a lone pair of a Lewis base or an anion. It involves a region of positive electrostatic potential, labeled a σ-hole, on the extension of one of the covalent bonds to the atom. The σ-hole is due to the anisotropy of the atom's charg...
Article
Halogen bonding is a noncovalent interaction that is receiving rapidly increasing attention because of its significance in biological systems and its importance in the design of new materials in a variety of areas, for example, electronics, nonlinear optical activity, and pharmaceuticals. The interactions can be understood in terms of electrostatic...
Article
Full-text available
A synchronous, concerted chemical process is rigorously divided by the reaction force F(R), the negative gradient of V(R), into “reactant” and “product” regions which are dominated by structural changes and an intervening “transition” region which is electronically intensive. The reaction force constant κ(R), the second derivative of V(R), is negat...
Article
The isomeric di-1,2,3,4-tetrazine tetraoxides DTTO and iso-DTTO have aroused considerable interest in recent years as potential energetic compounds, due to their predicted high densities and heats of formation and superior detonation properties. While neither has yet been synthesized, it has been suggested that the N→O linkages on alternate nitroge...
Article
In designing proposed new explosives, we seek a balance between high detonation performance and low sensitivity. Accordingly we focus upon (1) planar molecules, for better packing efficiency and reduced shear strain upon impact/shock, (2) high nitrogen content, for greater density and enthalpy of formation, (3) N->O linkages rather than NO2 or ONO2...
Article
The reaction force. F(R) and the reaction force constant. κ(R) are intrinsic and universal properties of any process that can be represented by a potential energy profile. V(R), where. R is a reaction coordinate. F(R) is the negative gradient of. V(R) along. R;. κ(R) is the second derivative of. V(R). The minima and maxima of. F(R), which correspon...
Article
Many covalently-bonded atoms of Groups IV–VII have regions of positive electrostatic potential (σ-holes) opposite to the bonds, along their extensions. Through these positive regions, the atoms can interact highly directionally with negative sites. (Halogen bonding, in which the σ-hole is on a Group VII atom, is an example of this, and we suggest t...

## Citations

... [56] This is due to the molecules' increased ability to accept electrons more readily, which will most likely be reflected in their reactivity. [57,58] It should be noted, however, that while ICT and energy gap (E g ) correlate with a molecule's chemical reactivity in general, they do not always reflect its biological activity, as the latter is dependent on a variety of other parameters and effects. [59] The time dependent-DFT results show that, the ICT values of (3 a-j) is lower than that of (11 a-j), which makes (11 a-j) molecules have a greater potency towards the bacteria strains than (3 a-j). ...
... Several reviews have been published on noncovalent interactions such as halogen bonding, 23 chalcogen bonding, 24 pnictogen bonding, 25 and tetrel bonding; 26 most of them are based on their applications in crystallography, synthetic chemistry, and materials chemistry. [27][28][29] A paucity is felt concerning reports dealing with the NCIs apart from H-bonds and those involving pelectrons in proteins and nucleic acids. This review summarizes the efforts of several research groups, including our own, to use these NCIs in studying the structure and dynamics of biomolecules. ...
... Known non-covalent interactions have different bonding characteristics; some are called -hole interactions [24,25], others -hole interactions [24,[26][27][28][29], and van der Waals interactions [30][31][32][33][34]. The latter are generally dispersive, with a binding energy  -1.0 kcal mol -1 , and can be of the -hole or the -hole type. ...
Citing article
... 46 The MESP calculated from ab initio wave functions were used to interpret the protonation of formamide, to assess the difference in reactivity of some sites towards electrophilic reagents for five-membered heterocycles, and to compare different protonation sites in the nucleic acid bases such as adenine, thymine, and cytosine. 45,[47][48][49][50] Numerous MESP-based studies carried out by Politzer and Murray have contributed largely towards establishing MESP as a fundamental quantity 10,51 for the theoretical analysis of chemical reactivity, [51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67] such as analysis of nucleophilicity, crystal density, explosive nature of compounds, [68][69][70] noncovalent intermolecular interactions, etc. 71 Politzer et al. proposed the σ-hole interaction theory to describe noncovalent bonding scenarios arising from group 14 (tetrels), 15 (pnicogens), 16 (chalcogens), and 17 (halogens) elements. [72][73][74] Electrondeficient region that arises from the anisotropic distribution of electron density on the atom is described as σ-hole and such a site characterized by positive MESP interacts with negative MESP sites. ...
... A number of cases referred to above contained examples of Type-III interactions (sometimes called counter-intuitive interactions [78,183,184] in crystal lattices). In Fig. 24, another set of examples are given where covalently or coordinately bound Bi acts both as an acceptor and a donor of charge density when in close proximity. ...