Molecular electrostatics for probing lone pair-π interactions

Bovine carbonic anhydrase (bCA) inhibitors: Synthesis, molecular docking and theoretical studies of bisoxadiazole-substituted sulfonamide derivatives

This paper describes the in vitro inhibition potential of bisoxadiazole-substituted sulfonamide derivatives (6a-t) against bovine carbonic anhydrase (bCA) after they were designed through computational analyses and evaluated the predicted interaction via molecular docking. First, in silico ADMET predictions and physicochemical property analysis of the compounds provided insights into solubility and permeability, then density functional theory (DFT) calculations were performed to analyse their ionization energies, nucleophilicity, in vitro electron affinity, dipole moments and molecular interactions under vacuum and dimethyl sulfoxide (DMSO) conditions. After calculating the theoretical inhibition constants, IC50 values determined from enzymatic inhibition were found between 12.93 and 45.77 μM. Molecular docking evaluation revealed favorable hydrogen bonding and π-interactions of the compounds within the bCA active site. The experimentally most active compound, 6p, exhibited the strongest inhibitory activity with a theoretical inhibition constant value of 9.41 nM and H-bonds with Gln91, Thr198, and Trp4 residues and His63 Pi-cation interactions with His63 residues. Overall, the study reveals promising bCA blocking potential for the synthesized derivatives, similar to acetazolamide.

A Theoretical Investigation of Novel Sila- and Germa-Spirocyclic Imines and Their Relevance for Electron-Transporting Materials and Drug Discovery

A new class of spirocyclic imines (SCIs) has been theoretically investigated by applying a variety of quantum chemical methods and basis sets. The uniqueness of these compounds is depicted by various peculiarities, e.g., the incidence of planar six-membered rings each with two imine groups (two π bonds) and the incorporation of the isosteres carbon, silicon, or germanium spiro centers. Additional peculiarities of these novel SCIs are mirrored by their three-dimensionality, the simultaneous occurrence of nucleophilic and electrophilic centers, and the cross-hyperconjugative (spiro-conjugation) interactions, which provoke charge mobility along the spirocyclic scaffold. Substitution of SCIs with strong electron-withdrawing substituents, like the cyano group or fluorine, enhances their docking capability and impacts their reactivity and charge mobility. To gain thorough knowledge about the molecular properties of these SCIs, their structures have been optimized and various quantum chemical concepts and models were applied, e.g., full NBO analysis and the frontier molecular orbitals (FMOs) theory (HOMO-LUMO energy gap) and the chemical reactivity descriptors derived from them. For the assessment of the charge density distribution along the SCI framework, additional complementary quantum chemical methods were used, e.g., molecular electrostatic potential (MESP) and Bader's QTAIM. Additionally, using the aromaticity index NICS (nuclear independent chemical shift) and other criteria, it could be shown that the investigated cross-hyperconjugated sila and germa SCIs are spiro-aromatics of the Heilbronner Craig-type Möbius aromaticity.

Naphthoquinones biflorin and bis-biflorin (Capraria biflora) as possible inhibitors of the fungus Candida auris polymerase: molecular docking, molecular dynamics, MM/GBSA calculations and in silico drug-likeness study

A new worldwide concern has emerged with the recent emergence of infections caused by Candida auris. This reflects its comparative ease of transmission, substantial mortality, and the increasing level of resistance seen in the three major classes of antifungal drugs. Efforts to create a better design for structure-based drugs that described numerous modifications and the search for secondary metabolic structures derived from plant species are likely to reduce the virulence of several fungal pathogens. In this context, the present work aimed to evaluate in silico two naphthoquinones isolated from the roots of Capraria biflora, biflorin, and its dimmer, bis-biflorin, as potential inhibitors of Candida auris polymerase. Based on the simulation performed with the two naphthoquinones, biflorin and bis-biflorin, it can be stated that bis-biflorin showed the best interactions with Candida auris polymerase. Still, biflorin also demonstrated favorable coupling energy. Predictive pharmacokinetic assays suggest that biflorin has high oral bioavailability and more excellent metabolic stability compared to the bis-biflorin analogue. constituting a promising pharmacological tool.Communicated by Ramaswamy H. Sarma.

Probing the Directionality of S···O/N Chalcogen Bond and Its Interplay with Weak C-H···O/N/S Hydrogen Bond Using Molecular Electrostatic Potential

The directionality of the chalcogen bond (Ch-bond) formed by S and its interplay with other weak interactions have important chemical and biological implications. Here, dimers made of CH₃-S-X and O/N containing nucleophiles are studied and found to be stabilized by coexisting S···O/N and C-H···O/N interactions. Based on experimentally accessible electron density and molecular electrostatic potentials (MESPs), we showed that reciprocity between S···O/N and C-H···O/N interactions in the stability of cumulative molecular interaction (ΔE) was dependent on the strength of the σ-hole on S (V_s,max). Direct correlation between ΔE of dimers with V_s,max of S supports the electrostatic nature of the Ch-bond. Such interplay of the Ch-bond is necessary for its directionality in complex nucleophiles (carbonyl groups) with multiple electron-rich centers, which is explained using MESP. A correlation between the MESP minima in the π-region and the strength of the S-π interaction explains the directional selectivity of the Ch-bond.

A phenyl S-Te bond with unique redox activity in dilute electrolyte of a lithium battery

Phenyl tellurosulfide (PhS-TePh) was used to study the redox activity of the S-Te bond in lithium batteries. PhS-TePh formed a dynamic covalent network during lithiation, which provided a balance between responsiveness and stability to facilitate ion and electron transfer, enabling Li/PhS-TePh cells to achieve stable cycling and excellent rate performance in dilute electrolyte.

Finding critical points and reconstruction of electron densities on grids

The quantum theory of atoms in molecules (QTAIM), developed by Bader and co-workers, is one of the most popular ways of extracting chemical insight from the results of quantum mechanical calculations. One of the basic tasks in QTAIM is to locate the critical points of the electron density and calculate various quantities (density, Laplacian, etc.) on them since these have been found to correlate with molecular properties of interest. If the electron density is given analytically, this process is relatively straightforward. However, locating the critical points is more challenging if the density is known only on a three-dimensional uniform grid. A density grid is common in periodic solids because it is the natural expression for the electron density in plane-wave calculations. In this article, we explore the reconstruction of the electron density from a grid and its use in critical point localization. The proposed reconstruction method employs polyharmonic spline interpolation combined with a smoothing function based on the promolecular density. The critical point search based on this reconstruction is accurate, trivially parallelizable, works for periodic and non-periodic systems, does not present directional lattice bias when the grid is non-orthogonal, and locates all critical points of the underlying electron density in all tests studied. The proposed method also provides an accurate reconstruction of the electron density over the space spanned by the grid, which may be useful in other contexts besides critical point localization.

Combined study of docking and molecular dynamics against DNV-3 SN1 protein by bixinoids

Dengue (DENV), Zica virus (ZIKV), and Chikungunya fever (CHIK) are tropical diseases that have caused a lot of problems in general worldwide. Transmitted by mosquitoes of the species Aedes aegypti and albopictus, they have not been completely eradicated in the country, and their proliferation has only increased in the Northeast region. Within the structure of the virus, it is possible to verify the presence of glycoprotein SN1, which is responsible for its replication. If this macromolecule is inhibited using a specific or complex linker, it can interrupt its replication activity. An alternative to this problem has been using structures derived from natural products that have pharmacological properties. A dynamic and molecular docking combined study used computational simulation in the four isomeric forms of bixin against the SN1 protein. The Z,E-bixin and E,E-bixin isomers, both with affinity energy -6.7 and -6.5 Kcal/mol, presented the best results. Thus, bixin and its isomers, found in annatto seeds, maybe an initial proposal in the search for prototype compounds to study to fight this lethal virus in the future.Communicated by Ramaswamy H. Sarma.

Synthesis Characterization and X-ray Structure of 2-(2,6-Dichlorophenylamino)-2-imidazoline Tetraphenylborate: Computational Study

The title compound tetraphenylborate salt of clonidine (Catapres®), 2-(2,6-dichlorophenylamino)-2-imidazoline tetraphenylborate (3), was prepared in 76 % yield by the reaction of 2-(2,6-dichlorophenylamino)-2-imidazoline hydrochloride (clonidine hydrochloride) (1) with sodium tetraphenylborate (2) in deionized water through anion exchange reaction at ambient temperature. The structure of the title borate salt was characterized by UV, thermal analysis, mass and NMR analyses. White crystals of (3) suitable for an X-ray structural analysis were obtained by slow growing from acetonitrile. The molecular structure of the titled compound (3) was crystallized in the acetonitrile, P21/c, a = 9.151 (3) Å, b = 12.522 (3) Å, c = 25.493 (6) Å, β = 105.161 (13)° V = 2819.5 (13) Å3, Z = 4. A DFT quantum chemistry calculation method was employed to investigate the interaction mechanism of clonidine with tetraphenylborate. The stable configurations of the complexes of clonidine with tetraphenylborate with electrostatic interactions were obtained. Finally, the interaction strength and type of the complexes were studied through the reduced density gradient (RDG) function. This study provides new theoretical insight into the interaction mechanism and a guide for screening and designing the optimal clonidine and tetraphenylborate reacting to form the complex.

Hydration patterns of rings in drugs and relationship to lipophilicity: A DFT study

Rings are one of the major scaffold components of drugs in medicinal chemistry, due to their unique electronic distribution, scaffold rigidity, and three-dimensionality while lipophilicity is considered as a vital parameter of rings that can influence the reactivity, metabolic stability, and toxicity. We have analyzed the electronic features, hydration patterns, solvation effect and lipophilicity data for 51 most widely used ring systems in drugs. Molecular electrostatic potential (MESP) topology analysis has been used to assess the electronic distribution in rings which provided an easy interpretation of the most suitable hydration patterns of the ring with H₂ O molecule. Further, the global minimum of ring…H₂ O complex has been utilized to predict lipophilicity (logP) with the incorporation of implicit solvation effect. Classification of ring systems based on their molecular weight into four categories, viz. small ring 'sr', medium ring 'mr', large ring 'lr' and extra large ring 'xlr' systems has led to the finding of strong correlations between logP and hydration energy with R = 0.942, 0.933, 0.968 and 0.933, respectively. The micro solvation model is found to be useful for locating the hydrophobic-hydrophilic border for each category of rings in terms of hydration energy whereas the implicit solvation model used for two solvents, n-octanol and water on the most stable hydrated structure led to a global correlation between logP and solvation energy ratio. This correlation predicts a limiting logP value -7.03 for the most hydrophilic ring system and also suggests a clear partitioning of the ring molecules into hydrophobic and hydrophilic classes. The MESP topology-guided approach to understand the electronic features and hydration patterns of rings in drugs lead to powerful predictions on their lipophilicity behavior.

The use of electrostatic potential at nuclei in the analysis of halogen bonding

Molecular electrostatic potential data at interacting nuclei provide strong evidence of bond formation in many intermolecular halogen bonded complexes.

BF3 -Catalyzed Mukaiyama aldol reaction of acetaldehyde with 2-siloxy-1-propene

The Mukaiyama aldol reaction is a powerful tool for the construction of the carbon-carbon bond and the formation of β-hydroxycarbonyl compounds. In this work, the mechanism of acetaldehyde and 2-siloxy-1-propene both in the absence and presence of the catalyst BF₃ was investigated based on density functional theory. The mechanism includes two major steps: the formation of the carbon-carbon bond and the removal of SiH₃ /BF₂ by water. The energy barrier of the carbon-carbon bond formation process in the presence of BF₃ is obviously lower, indicating that BF₃ is a good catalyst for this reaction. In terms of molecular configuration, the different tensions between the five-membered-ring and six-membered-ring can be considered as the possible reason for the catalytic effect of BF₃ . In terms of charge transfer, the charges of natural population analysis in the carbon atom of the carbonyl group in acetaldehyde becomes more positive, which is easier to attack by nucleophiles and promote the nucleophilic process.

Macrolactonization Reactions Driven by a Pentafluorobenzoyl Group*

Macrolactones constitute a privileged class of natural and synthetic products with a broad range of applications in the fine chemicals and pharmaceutical industry. Despite all the progress made towards their synthesis, notably from seco-acids, a macrolactonization promoter system that is effective, selective, flexible, readily available, and, insofar as possible, compatible with manifold functional groups is still lacking. Herein, we describe a strategy that relies on the formation of a mixed anhydride incorporating a pentafluorophenyl group which, due to its high electronic activation enables a convenient access to macrolactones, macrodiolides and esters with a broad versatility. Kinetic studies and DFT computations were performed to rationalize the reactivity of the pentafluorophenyl group in macrolactonization reactions.

Electrostatic Potential Topology for Probing Molecular Structure, Bonding and Reactivity

Following the pioneering investigations of Bader on the topology of molecular electron density, the topology analysis of its sister field viz. molecular electrostatic potential (MESP) was taken up by the authors’ groups. Through these studies, MESP topology emerged as a powerful tool for exploring molecular bonding and reactivity patterns. The MESP topology features are mapped in terms of its critical points (CPs), such as bond critical points (BCPs), while the minima identify electron-rich locations, such as lone pairs and π-bonds. The gradient paths of MESP vividly bring out the atoms-in-molecule picture of neutral molecules and anions. The MESP-based characterization of a molecule in terms of electron-rich and -deficient regions provides a robust prediction about its interaction with other molecules. This leads to a clear picture of molecular aggregation, hydrogen bonding, lone pair–π interactions, π-conjugation, aromaticity and reaction mechanisms. This review summarizes the contributions of the authors’ groups over the last three decades and those of the other active groups towards understanding chemical bonding, molecular recognition, and reactivity through topology analysis of MESP.

Interaction of Cun, Agn and Aun (n = 1-4) nanoparticles with ChCl:Urea deep eutectic solvent

In this study, the interaction of noble metal nanoparticles (M_n, M = Cu, Ag, and Au; n = 1-4) with ChCl:Urea deep eutectic solvent was investigated using density functional theory (DFT) method. We find that ChCl:Urea mostly interact with the M_n nanoparticles through [Cl]^- anion ([Cl]^-…M_n) and nonconventional H-bonds of C-H⋯M_n and N-H⋯M_n. NBO, QTAIM, NCI and EDA analyses show that [Cl]^-…M_n interactions are stronger than the nonconventional H-bonds interactions. Our results indicate that the nature of [Cl]^-…M_n interactions is electrostatic, while the nonconventional H-bonds of C-H⋯M_n and N-H⋯M_n are van der Waals in nature. The negative values of enthalpy (ΔH) and free energy (ΔG) for the ChCl:Urea…M_n complexes reveal that the formation of ChCl:Urea…M_n complexes is exothermic and proceeds spontaneously. The calculation of binding energy (ΔE_b) of M_n nanoparticles with ChCl:Urea shows that the strength of interaction of Au_n nanoparticles with ChCl:Urea is more favorable than Cu_n and Ag_n, following the order ChCl:Urea…Au_n > ChCl:Urea…Cu_n > ChCl:Urea…Ag_n. Furthermore, the ΔE_b, ΔH and ΔG values enhance with increasing nanoparticle size from n = 1 to n = 4, ChCl:Urea…M₄> ChCl:Urea…M₃> ChCl:Urea…M₂> ChCl:Urea…M₁ (M = Cu, Ag, and Au).

Cospatial σ-Hole and Lone Pair Interactions of Square-Pyramidal Pentavalent Halogen Compounds with π-Systems: A Quantum Mechanical Study

In the spirit of the mounting interest in noncovalent interactions, the present study was conducted to scrutinize a special type that simultaneously involved both σ-hole and lone pair (lp) interactions with aromatic π-systems. Square-pyramidal pentavalent halogen-containing molecules, including X-Cl-F4, F-Y-F4, and F-I-X4 compounds (where X = F, Cl, Br, and I and Y = Cl, Br, and I) were employed as σ-hole/lp donors. On the other hand, benzene (BZN) and hexafluorobenzene (HFB) were chosen as electron-rich and electron-deficient aromatic π-systems, respectively. The investigation relied upon a variety of quantum chemical calculations that complement each other. The results showed that (i) the binding energy of the X-Y-F4···BZN complexes increased (i.e., more negative) as the Y atom had a larger magnitude of σ-hole, contrary to the pattern of X-Y-F4···HFB complexes; (ii) the interaction energies of X-Y-F4···BZN complexes were dominated by both dispersion and electrostatic contributions, while dispersive interactions dominated X-Y-F4···HFB complexes; and (iii) the X4 atoms in F-I-X4···π-system complexes governed the interaction energy pattern: the larger the X4 atoms were, the greater the interaction energies were, for the same π-system. The results had illuminating facets in regard to the rarely addressed cases of the σ-hole/lp contradictory scene.

Theoretical study of hydrogen bonding interactions in substituted nitroxide radicals

Interaction energy (E_int) of hydrogen bonded complexes of nitroxide radicals can be assessed in terms of the deepest minimum of molecular electrostatic potential (V_min).

The conformational change of Plukenetia conophora oil derivatives and their acidic resistance, intra-fragment interactions, stability in different solvent media

The synthesis of derivatives of bio-based lubricants from vegetable oil as an alternative to petroleum oil is significant due to the oil crisis, global warming, higher demand and serious environmental threat. In this study, the molecular properties of three derivatives of oil derived from Plukenetia conophora seeds, namely Plukenetia conophora oil (PK), rpoxidised Plukenetia conophora oil (EP) and poly(hydroxybutanethiol-ether) derivative of Plukenetia conophora oil (BP), were examined in acidic media and crystal form. The derivative BP has the highest resistance to acidic attack as evident from their poor interaction with acidic H₃O⁺ from both HCl and HNO₃. BP also has the best tendency of forming a crystal as evident from the lowest atomic diffusion in crystal model (L12). However, the result of the molecular electrostatic potential (MESP) analysis shows that BP has more electron-deficient surface compare to EP derivatives. The derivative BP is also found to have the lowest potential energy and higher root means square deviation (RMSD) of its atoms. Density clustering analysis further confirms that BP did not retain its most stable conformation for a longer period of simulation compared to PK and EP. The most visited conformation from the hierarchical and density clustering also corresponds to the minimum potential energy on the potential energy surface.Graphical abstract.

Multicomponent and multicatalytic asymmetric synthesis of furo[2,3-b]pyrrole derivatives: further insights into the mode of action of chiral phosphoric acid catalysts

Multicomponent and multicatalytic reactions are those processes that try to imitate the way the enzymatic machinery transforms simple building blocks into complex products. The development of asymmetric versions of these reactions is a step forward in our dream of mirroring the exquisite selectivity of biological processes. In this context, the present work describes a new reaction for the asymmetric synthesis of furo[2,3-b]pyrrole derivatives from simple 3-butynamines, glyoxylic acid and anilines in the presence of a dual catalytic system, formed from a gold complex and a chiral phosphoric acid. Computations, aimed to understand the exceptional performance of 9-anthracenyl-substituted BINOL-derived phosphoric acid catalyst, suggest a fundamental role of non-covalent interactions being established between the catalyst and the reagents for the outcome of the multicomponent process. The linear geometry of the anthracenyl substituent along with the presence of an electron-withdrawing group in the aniline and an aromatic substituent in the 3-butynamine derivative seem to be key structural factors to explain the experimental results and, particularly, the high stereoselectivity.

Microhydration of a Carbonyl Group: How does the Molecular Electrostatic Potential (MESP) Impact the Formation of (H2O)n:(R2C═O)Complexes?

The presence of a carbonyl group in a molecule usually leads to the identification of a π-hole on the molecular electrostatic potential (MESP) of the species. How does this electrophilic site influence the formation of microhydrated complexes? To address this point, a panel of R₂CO solutes with various MESPs was selected, and we identified the structures and properties of several complexes containing one, two, three and six water molecules. The following solutes were considered in the present study: H₂CO, F₂CO, Cl₂CO,(NC)₂CO and H₂C═CO. Geometry optimizations and frequency calculations were carried out at the LC-ωPBE/6-311++G(d,p) level, with the GD3BJ empirical correction for dispersion. For a number of n water molecules around the R₂CO solute, the structure and the features of the most stable (H₂O)_n:(R₂CO) complexes are highly dependent on the MESP of the isolated R₂CO solute. The formation of pi-hole bondings appears to play a decisive role in the initiation of a three-dimensional organization of water molecules around the solute.

Electrostatic Topographical Viewpoint of π-Conjugation and Aromaticity of Hydrocarbons

A molecular electrostatic potential (MESP) topographical study has been conducted for a variety of conjugated hydrocarbons at B3LYP/6-311+G(d,p) level of theory to understand their π-conjugation features and aromaticity. The value of MESP minimum (V_m) is related to the localized and delocalized distribution of π-electron density. The V_m values are located interior to the rings in polycyclic benzenoid hydrocarbons (PBHs), whereas they lie outside the boundary of the rings in antiaromatic and in fused systems consisting of aromatic and antiaromatic moieties. The V_m points lie on top and bottom of the π-regions in linear polyenes and annulenes, while a degenerate distribution of CPs around the midpoint region of triple bonds is observed in alkynes. The eigenvalues λ₁, λ₂, and λ₃ of the Hessian matrix at V_m(MESP minima) are used to define the aromatic character of the cyclic structures. The eigenvalues follow the trend λ₁ ≫ λ₂ > λ₃ ≅ 0 in PBHs, λ₁ > λ₂ > λ₃ ≅ 0 in linear polyenes, and λ₁ > λ₂ > λ₃ ≠ 0 in antiaromatic systems. The difference in the aromatic character of PBHs from that of benzene is related to the deviations Δλ₁, Δλ₂, and Δλ₃. The total deviation ∑_i=1³Δλ_i is found to be ≤ 0.011 au for all aromatic systems and lies between 0.011 and 0.035 au for all nonaromatic systems. For antiaromatic systems, its value is found to be above 0.035 au. Further, ∑_i=1³Δλ_i gives a direct interpretation of Clar's aromatic sextet structures for PBHs. In summary, MESP topography mapping is a powerful technique to quantify the localized and delocalized π-electron distribution in a variety of unsaturated hydrocarbon systems.

Hidden Dicarbene Nature of Acetylenes and Captodative Bonding on Carbon

DFT derived molecular electrostatic potential (MESP), ¹³C NMR chemical shift (δ), bond order and coordination reactions show that alkynes (RCCR) attain 1,2-dicarbene nature during CCR angle bending. Alkyne carbon atoms of bent structures exhibit MESP features unique to lone-pair bearing atoms, δ around 200 ppm typical for carbene centers and large reduction in CC triple bond character. Lone pair bearing atoms of R substituents enhance the carbene character. The bent alkynes can be trapped with Lewis acids (BH₃, BF₃, AlF₃ and AlCl₃) as the lone pairs developed on carbon centers provide strong donor type dative bonding. The dative bond gives a formal valence electron count six on carbon and suggests the for-mation of acceptor type dative bonding to carbon from Lewis base (NH₃). Reaction of alkynes with (Lewis acid-Lewis base) systems yield (Lewis acid)₂-Alkyne-Lewis base)₂ complexes which are exothermic and exergonic for many cases. These complexes are examples of captodative carbon(II) compounds.

Co-operativity in non-covalent interactions in ternary complexes: a comprehensive electronic structure theory based investigation

The structure and stability of various ternary complexes in which an extended aromatic system such as coronene interacts with ions/atoms/molecules on opposite faces of the π-electron cloud were investigated using ab initio calculations. By characterizing the nature of the intermolecular interactions using an energy decomposition analysis, it was shown that there is an interplay between various types of interactions and that there are co-operativity effects, particularly when different types of interactions coexist in the same system. Graphical abstract Weak OH-π, π-π and van der Waals-π ternary systems are stabilized through dispersion interactions. Cation-π ternary systems are stabilized by through-space electrostatic interactions.

Through bond and through space interactions in dehydro-diazine radicals: a case study of 3c-5e interactions

Owing to the 3c-5e (3-centred-5-electrons) interactions between two nitrogen lone pairs and a radical electron, the dehydrodiazine radical isomers are very interesting from the fundamental point of view. Among them, pyrimidine has three (1a-1c), pyridazine has two (2a and 2b) and pyrazine has only one (3a) radical isomer. Based on quantum chemical calculations at the (U)B3LYP, (U)M06-2X, (U)BLYP, CBS-QB3 and (U)CCSD(T) levels with cc-pVTZ as the basis set, we found the 4-dehydropyrimidine (1b) radical to be the most stable isomer among the three pyrimidine radicals, followed by the 2-dehydropyrimidine (1a) and 5-dehydropyrimidine (1c) radical isomers. In the case of pyridazine, 3-dehydro radical isomer (2a) is more stable than 4-dehydropyridazine (2b). Bond dissociation energy (BDE) calculations and estimation of radical stabilization energies (RSE) using isodesmic reactions revealed the stability order among the six isomeric diazine radicals as 1c < 2b < 2a < 1a < 3a < 1b. Spin densities at each radical centre and non-zero values at nitrogen centres provided information about the extent of delocalization of radical electrons, which was consistent with the relative stability order of all the isomers. The multiconfigurational CASSCF and natural bond orbital (NBO) calculations suggested the presence of direct through space interactions (between lone pairs and a radical, TS) that play a dominant role over the through bond (through intervening bonds, TB) interactions in deciding the stability order. To confirm these results, we have also estimated the proton affinities (PAs) for each nitrogen atom and compared them with their respective parent diazines, where lowering of the PA values convincingly envisaged the extent and strength of interactions between the nitrogen and radical centre. Atoms-in-molecules (AIM) analysis and estimation of hyperfine coupling constants have also been performed to verify these results. All these results showed that the through space interaction between the lone pair and the radical electron is very important for the electronic structural and stability aspects in dehydrodiazine radicals.