Hydroxy-substituted aromatic N-heterocycles, including hydroxy pyridine (py), dihydroxy naphthyridines (nt), and trihydroxy pyridonaphthyridines (pn), have been investigated for their potential as CO2 adsorbents using density functional theory (DFT) calculations. Building on the pioneering work of Luo et al., who demonstrated exceptional CO2 capture capacities in pyridine-containing anion-functionalized ionic liquids, this study extends the exploration to a broader range of N-heterocycles. These N-heterocycles exhibit exceptional CO2 capture capabilities, driven by cooperative interactions between nitrogen and oxygen centres with CO2. The adsorption capacity increases with the number of nitrogen centres and hydroxy groups, with py, nt, and pn systems binding one, two, and three CO2 molecules, respectively. Notably, anionic N-heterocycles exhibit dramatically improved CO2 adsorption compared to their neutral counterparts, forming covalent bonds with CO2. The presence of counter cations, such as lithium or tetramethylphosphonium ions, further stabilizes CO2 adsorption, resulting in shorter interaction distances and higher exergonic free energy values. Solvent effects modeled using monoethanolamine (MEA) indicate a modest reduction in interaction energies for neutral and anionic systems, while ion-paired systems exhibit enhanced CO2 affinity in solution. Additionally, molecular electrostatic potential (MESP) analysis highlights the key adsorption sites and charge delocalization mechanisms that facilitate CO2 capture. The study also finds that enol-keto transformations, which could lead to CO2 conversion into carboxylates, are energetically unfavorable due to the loss of aromatic stability. These findings underscore the potential of hydroxy-substituted N-heterocycles, particularly in their anionic and cation-stabilized forms, as promising candidates for efficient CO2 capture. The insights gained from this study provide valuable guidelines for the design of next-generation CO2 sequestration materials and highlight new directions for experimental validation and real-world applications.

The Hammett substituent parameter (σp) is fundamental to physical organic chemistry but often suffers from inconsistencies in experimental determination across diverse substituents. This study presents a quantum chemical approach for estimating σp values using 1H NMR chemical shift differences (Δδ) in hydrogen-bonded 2-pyridone heterodimers. Using density functional theory (M06L/6-311++G(d,p)), we examined four dimer topologies─da, db, dc, and dd─and found that the Δδ values in the db configuration, where the substituent is spatially remote from the hydrogen-bonding region, exhibit the strongest correlation with σp. This aligns with the sterically free nature of σp. Additional correlations are observed between σp and structural (Δr), energetic (ΔE), and electronic descriptors (MESP, QTAIM) of CO···HN hydrogen bonds. Among the topologies, db and dc systems provide the most reliable correlations, while deviations in da and dd dimers arise due to proximity-induced secondary interactions. The NMR-derived substituent constant, σp(NMR), was computed for a diverse set of 99 substituents, offering a unified, reliable, and computationally efficient framework for predicting and refining the Hammett constants. These findings underscore the potential of NMR chemical shifts as a powerful experimental and computational tool for quantifying substituent effects and enhance the theoretical foundation for structure-reactivity relationships in organic chemistry.

Ladderenes, unique polymers composed of fused cyclobutane rings, exhibit promising properties for energy storage applications, including reversible redox behavior and structural tunability. This density functional theory (DFT) study investigates the formation of ladderenes via gold(I)-catalyzed alkyne-alkene coupling reactions. Our calculations reveal a step-wise chain propagation mechanism where the alkene product of each step reacts with a ligand-gold-alkyne complex, leading to the sequential addition of cyclobutene units. We demonstrate that electron-withdrawing substituents on the alkynes, such as chlorine, facilitate the dissociation of the gold catalyst (PMe3Au+) from the cyclobutene adduct, enhancing catalytic efficiency. Solvent effects are also shown to significantly influence the reaction energetics. This finding highlights the significant impact of alkyne substitution on the catalytic cycle. The inherent exothermicity of ladderene formation, coupled with their unique structural features, suggests their potential for storing energy in the form of "covalently condensed acetylene".

A theoretical investigation on the cooperativity of a series of binary, ternary, and quaternary complexes interconnected by pnicogen bonds has been conducted using calculations at the M06-2X/aug-cc-pVTZ level of density functional theory. By measuring changes in the molecular electrostatic potential (MESP) at the nucleus of interacting atoms in all of the complexes, it is possible to quantify the substantial reorganization of the electron density triggered by the formation of pnicogen bonds. The positive change in MESP, indicating a loss of electron density from the donor molecule in a dimer, facilitates the acceptance of electron density from a third molecule, resulting in the formation of a ternary complex with a stronger pnicogen bond compared to the one present in the binary complex. Similarly, the acceptor molecule in a dimer with a negative change in MESP showed an enhanced tendency to donate electron density to an electron-deficient third molecule. The MESP analysis provided valuable insights into the donor/acceptor characteristics of pnicogen bonds within the quaternary complexes. The proposed MESP hypotheses are consistent with the positive cooperativity observed in the pnicogen-bonded clusters. To quantify the changes in MESP, both at the donor atom (Delta V-donor) and the acceptor atom (Delta V-acceptor), for all pnicogen bonds in the cluster, the total change in MESP (Delta Delta V-n) was measured as Delta Delta V-n = Sigma(Delta V-donor)-Sigma(Delta V-acceptor). Remarkably, Delta Delta V-n exhibited a strong linear relationship with the sum of the bond energies of the pnicogen bonds in the cluster. This establishes the MESP analysis as a robust approach for understanding the strength and cooperative behavior of pnicogen-bonded clusters. Additionally, the MESP features provided clear evidence of pnicogen bond formation, further supporting the reliability of this approach.

This study delves into the ring-opening reaction of two distinct diaryl-ring-pyran systems, referred to as dr(n)p(1) and dr(n)p(2), where the term 'ring' encompasses aromatic, nonaromatic, or antiaromatic motifs. These systems transform into the corresponding cis-ortho quinonoid systems, denoted as c-dr(n)q(1) and c-dr(n)q(2). Homodesmotic pairs (dr(n)p(1), dr(n)p(2)) and (c-dr(n)q(1), c-dr(n)q(2)) are categorized as (aromatic, nonaromatic), (aromatic, partially aromatic), (antiaromatic, nonaromatic), and (nonaromatic, nonaromatic), with their energy difference representing aromatization energy (E-aroma). Using reliable density functional theory, E-aroma is assessed for various aromatic and antiaromatic ring motifs, including borderline cases and nonaromatic structures. For example, benzene exhibits an E-aroma of 23.4 kcal/mol, indicating 3.9 kcal/mol aromatic stabilization per CC bond, while cyclobutadiene shows -29.9 kcal/mol, indicating a 7.5 kcal/mol destabilization of the CC bond. This approach extends to evaluating global and local aromatic stabilization effects in polycyclic hydrocarbons, nonbenzenoid systems, and heterocyclic compounds. Additionally, variation in H-1 NMR chemical shift (delta(avg)) correlates with E-aroma, suggesting that a -1.0 ppm shift corresponds to 24.2 kcal/mol aromatization energy. UV-vis absorption maxima difference (Delta lambda(avg)) correlates linearly with E-aroma, enabling direct assessment of aromatization energy from UV-vis spectra using suitable homodesmotic pairs. This comprehensive approach enhances our understanding of structural, energetic, and spectroscopic aspects of aromatic and antiaromatic systems.

We define Vn as the molecular electrostatic potential (MESP) at the nucleus of a free atom, calculated excluding the contribution of that nucleus charge. The Vn value at the nucleus of a free atom and that within the atom-in-molecule state show substantial difference (Delta Vn) due to alterations in the electronic configuration of the atom resulting from molecular bonding. Thus, variations in molecular structure and bonding lead to differing Delta Vn values for the same type of atoms in molecules. The Vn analysis focuses on frequently occurring ring structures in drugs and several drug molecules using density functional theory (DFT) at the M06L/6-311++G(d,p) level. The summation of Delta Vn for all heteroatoms acting as hydrogen bond acceptors (HBA) yields sigma Delta Vn(A), while sigma Delta Vn(H) represents the cumulative sum of Delta Vn for hydrogen atoms participating in hydrogen bond donors (HBD) and those in C-H bonds near heteroatoms. The total hydrogen bond propensity of a drug molecule (EHBP) is predicted by EHBP = 0.05 (sigma Delta Vn(A) - sigma Delta Vn(H)) - 7.68n. This equation is derived using interaction energy (sigma Eint) calculations for 'n' configurations of twenty ring moleculeMIDLINE HORIZONTAL ELLIPSISH2O complexes. The EHBP and sigma Eint showed a strong linear relationship with R = 0.974. Further, the EHBP equation is validated using the sigma Eint data of FDA-approved oral drugs. The EHBP prediction, solely based on MESP data, ranges from -2.3 to -131.5 kcal mol-1 for 193 FDA-approved oral drugs. Most orally administered drugs adhering to Lipinski's rule of five criteria typically fall within the EHBP range of -16.0 to -84.0 kcal mol-1. The study also derived a relationship between EHBP and Lipinski's rule of five (Ro5) parameters by incorporating a new parameter that accounts for hydrogen atoms participating in OwMIDLINE HORIZONTAL ELLIPSISH interactions from CH groups. This research presents a robust MESP-based approach for predicting hydrogen bond propensity in drug molecules, complementing drug design and optimization efforts. The correlation with Lipinski's rule of five parameters underscores the importance of hydrogen bond interactions in drug-likeness. Molecular electrostatic potential (MESP) topology data of chemical motifs in drugs provide prediction on their hydrogen bond propensity with H2O. The hydrogen bond propensity shows correlation with Lipinski's Ro5 parameters.

Gold catalysis enables selective chemical transformations with catalytic activity tunable through ligand selection. This study uses the density functional theory (DFT) to explore the impact of phosphine ligands (PR3) on gold(I)-catalyzed alkyne-alkene cyclobutene formation. We analyze the following key steps: (i) PR3-Au+ complexation, (ii) alkyne binding, (iii) alkene binding, (iv) C-C coupling transition state, (v) cyclobutene formation transition state, and (vi) cyclobutene dissociation. Molecular electrostatic potential (MESP) analysis provided a deeper understanding of electronic effects and revealed a strong correlation between the change in MESP at the gold nucleus (Delta V-N(Au)+) upon complex formation with various ligands and the corresponding complexation energy, as well as between the change in MESP at the alkyne carbon (Delta V-C) and the C-C coupling step activation barrier. This establishes MESP as a powerful tool for understanding ligand influence on catalysis. Our findings suggest that electron-donating phosphine ligands, combined with electron-withdrawing alkyne substituents, enhance catalyst turnover, promote cyclobutene product dissociation from the gold(I) complex, and facilitate catalyst regeneration. Solvent effects also play a crucial role. Bulky XPhos, JohnPhos, and CyJohnPhos ligands enhance gold(I) catalysis via steric protection, electron donation, and catalyst regeneration efficiency. In conclusion, this study provides insights into ligand effects in gold(I)-catalyzed cyclobutene formation, guiding future catalyst design.

An efficient method for the conversion of biphenyl acrylamides to dibenzoazepinones with −SCF 3 incorporation is described. This operationally simple radical cascade reaction employs CAN as an oxidant and exhibits good functional group tolerance. Substrates featuring −OCH 3 , −CH 3 , −Br or −Cl at the para ‐position of the aromatic ring exhibits a preference for an ipso ‐cyclization due to the intervention of DMSO in the reaction. Density functional theory (DFT) calculations provide valuable insights into the reaction's energetics and product selectivity.

Activating atmospheric dinitrogen (N2), a molecule with a remarkably strong triple bond, remains a major challenge in chemistry. This theoretical study explores the potential of superbase phosphines, specifically those decorated with imidazolin-2-imine ((ImN)3P) and imidazolin-2-methylidene ((ImCH)3P) to facilitate N2 activation and subsequent hydrazine (H2NNH2) formation. Using density functional theory (DFT) at the M06L/6-311++G(d,p) level, we investigated the interactions between these phosphines and N2. Mono-phosphine-N2 complexes exhibit weak, noncovalent interactions (-0.6 to -7.1 kcal mol-1). Notably, two superbasic phosphines also form high-energy hypervalent complexes with N2, albeit at significantly higher energies. The superbasic nature and potential for the hypervalency of these phosphines lead to substantial N2 activation in bis-phosphine-N2 complexes, where N2 is "sandwiched" between two phosphine moieties through hypervalent P-N bonds. Among the phosphines studied, only (ImN)3P forms an exothermic sandwich complex with N2, stabilized by hydrogen bonding between the ImN substituents and the central N2 molecule. A two-step, exothermic hydrogen transfer pathway from (ImN)3P to N2 results in the formation of a bis-phosphine-diimine (HNNH) sandwich complex. Subsequent hydrogen transfer leads to the formation of a bis-phosphine-hydrazine (H2NNH2) complex, a process that, although endothermic, exhibits surmountable activation barriers. The relatively low energy requirements for this overall transformation suggest its potential feasibility under the optimized conditions. This theoretical exploration highlights the promise of superbase phosphines as a strategy for metal-free N2 activation, opening doors for the development of more efficient and sustainable nitrogen fixation and utilization methods.

The study investigates the phenomenon of bond stretch isomerism (BSI) in complexes formed between alkali metals (Li, Na, K) and various non-aromatic, aromatic hydrocarbons, as well as heteroaromatic systems. The research employs density functional theory (DFT) calculations to optimize complex geometries and analyze their electronic structures using molecular electrostatic potential (MESP), charge, and spin density analyses. The results reveal that these complexes can exist in two distinct configurations: 'loose' long-bond isomers (lbi) that retain the original hydrocarbon geometry and 'tight' short-bond isomers (sbi) that undergo geometrical distortion upon complexation, with sbi generally being more stable. The interconversion between lbi and sbi occurs through a transition state. The study highlights the crucial role of electron transfer in BSI, with sbi involving valence electron transfer from the metal to the hydrocarbon, leading to zwitterionic radical complexes. In contrast, lbi exhibit a slight electron density transfer from the hydrocarbon to the metal. The presence of low-energy transition states between lbi and sbi suggests a dynamic shuttling mechanism for alkali metals, particularly Li, on hydrocarbon surfaces. The study identifies Li complexes as potential candidates for anode materials in batteries due to their stability and electron transfer properties, offering valuable insights into the design of advanced materials for energy storage applications. Bond-stretch isomers, resulting from organic molecules interaction with alkali metals, show varying carbon-metal bond lengths.

Members of a new class of bifunctional amino quaternary phosphonium salts have been synthesized and utilized as catalysts in aldol condensation reactions, as demonstrated herein. These secondary amines feature a phosphonium ion connected by a carbon chain, enabling the quaternary phosphonium ion to engage in distinct cooperative noncovalent interactions. These interactions work in tandem to stabilize different transition state complexes, exclusively controlling competing amine-catalyzed aldol pathways via the Mannich mechanism. Comprehensive mechanistic investigations were conducted through theoretical calculations. This study uncovers a proximity-driven catalytic mechanism in which the distance between the N and the P+ of the bifunctional catalyst emerges as a critical factor determining catalytic efficacy. The method has been demonstrated through its application to the total synthesis of several bioactive natural products.

The intrinsic donor–acceptor (D–A) character of pyrrole, indole, isoindole, azulene and aniline is utilized to develop oligomeric systems with enhanced D–A character.

Abstract A two-layer ONIOM(B3LYP/6-31G*:PM7) method is used to model the binding of several drug/drug-like molecules (L) at the SARS-CoV-2 S-protein: human ACE2 protein interface cavity. The selected molecules include a set of thirty-five ligands from the study of Smith and Smith which showed a high docking score in the range of −7.0 to −7.7 kcal/mol and another set of seven repurposing drugs, viz. favipiravir, remdesivir, EIDD, galidesivir, triazavirin, ruxolitinib, and baricitinib. The ONIOM model of the cavity (M) showed a highly polarized electron distribution along its top-to-bottom direction while Ls with lengths in the range 1.0 − 1.5 nm fitted well inside the cavity in a head-to-tail fashion to yield ML complexes. The ligands showed a large variation in the ONIOM-level binding energy (Eb), in the range −2.7 to −85.4 kcal/mol. The Eb of ML complexes better than −40.0 kcal/mol is observed for myricetin, fidarestat, protirelin, m-digallic acid, glucogallin, benserazide hydrochlorideseradie, remdesivir, tazobactum, sapropterin, nitrofurantoin, quinonoid, pyruvic acid calcium isoniazid, and aspartame, and among them the highest Eb −85.4 kcal/mol is observed for myricetin. A hydroxy substitution is suggested for the phenyl ring of aspartame to improve its binding behavior at the cavity, and the resulting ligand 43 showed the best Eb −84.5 kcal/mol. The ONIOM-level study is found to be effective for the interpretation of the noncovalent interactions resulting from residues such as arginine, histidine, tyrosine, lysine, carboxylate, and amide moieties in the active site and suggests rational design strategies for COVID-19 drug development. Communicated by Ramaswamy H. Sarma A quantum chemical treatment of the noncovalently-bonded drug and drug-like molecules at the interface of SARS-CoV2: human ACE2 receptor is described. It predicts that myricetin, fidarestat, protirelin, m-digallic acid, glucogallin, benserazide hydrochlorideseradie, remdesivir, tazobactum, sapropterin, nitrofurantoin, quinonoid, pyruvic acid calcium isoniazid, and aspartame have high binding affinity at the interface and also suggests a design strategy to modify aspartame for improved binding affinity.

There has been a notable surge of interest in the field of dye sensitized solar cells (DSSCs) in recent years due to their remarkable performance in indoor/ambient and diffused light conditions. A significant portion of these highly efficient indoor DSSCs employs organic dyes based on triphenylamine. In this study, we present the findings of our investigation on two metal-free D-pi-A organic dyes, namely triphenylamine (YK 10) and hexyloxy-substituted triphenylamine (YK 11), serving as electron donors. These dyes feature a 3,3 ''-dioctyl-2,2 ':5 ',2 ''-terthiophene pi-spacer and cyanoacetic acid as the anchoring group. In order to comprehensively assess the relationship between the molecular structure, physical properties, and solar cell performance, we conducted in-depth analysis involving photophysical, electrochemical, and theoretical studies. Our results indicate that these dyes possess the ability to effectively capture light within the visible spectrum and exhibit suitable energetic characteristics for efficient electron injection and dye regeneration. Through the utilization of density functional theory (DFT) modeling, we explored the interfacial adsorption configuration of the dyes on the TiO2 semiconductor, revealing the involvement of the cyano group in the anchoring mechanism for both sensitizers. Moreover, the intramolecular S horizontal ellipsis CN interaction in these dyes was verified through topological quantum-theory-of-atom-in-molecule (QTAIM) analysis, which facilitates additional intramolecular charge transfer pathways. The DSSCs incorporating YK 10 and YK 11 demonstrated power conversion efficiencies (PCEs) of 6.42 % and 6.22 %, respectively, under full sun illumination (100 mW/cm2). Remarkably, under both standard 1000 lux CFL and LED illumination conditions, YK 11 exhibited superior performance with PCEs of 8.29 % and 5.89 %, respectively, surpassing the efficiencies of YK 10, which achieved 7.50 % and 5.09 % efficiencies under the same conditions. Detailed investigation of structure-property relationship contributing towards photovoltaic performance in D-pi-A triphenylamine-organic dye based dye-sensitized solar cells under outdoor and indoor illumination conditions.image

Majority of the substituents in organic and organometallic chemistry are electron-withdrawing in nature toward substrates/ligands. Even for the most electron-donating neutral substituents such as N,N-dialkyl amino groups, the magnitude of electron donation is only nearly half of the magnitude of electron withdrawal by some of the most withdrawing groups. Therefore, development of highly electron-donating substituents promises the discovery of new chemistry. Density functional theory (DFT) study at the M06L/6-311++G(d,p) level in conjunction with molecular electrostatic potential (MESP) topology analysis unraveled the high electron donating nature of imidazolin-2-imine (X and X ') and imidazolin-2-methylidene (Y and Y ') types of moieties as substituents to benzene, pyridine, phosphine (PR3), and N-heterocyclic carbene (NHC). The MESP minimum (Vmin) is derived for aromatic pi-regions and lone-pair regions of the molecules, and the X-, X '-, Y-, and Y '-substituted systems showed a substantial increase in the negative character of Vmin compared to that of the corresponding unsubstituted systems. Multiple substitutions led to a further increase in the magnitude of Vmin, by 195% for benzene with tri-Y ' substitution, 541% for pyridine with tri-Y substitution, 162% for PH3 with tri-X ' substitution, and 23% for NHC with di-X ' substitution, which suggests the amazing electron donating ability of these substituents. The substituted benzene, pyridine, phosphine, and NHC behaved as very strongly coordinating ligands toward Li+, CuCl, and Cr(CO)3. The coordination energy is proportional to the electron richness of the ligands measured in terms of Vmin. The Vmin serves as an electronic parameter and leads to a priori prediction of the coordination reactivity of the ligands. The recent discovery of the complex of PMeX '' 2 (X '' = imidazolin-2-imine group) with C2 is also rationalized in terms of the high electron donating character of X ''. The substitution with imidazolin-2-imine and imidazolin-2-methylidene moieties suggests a powerful molecular design strategy toward the development of highly electron-rich substrates and ligands.

The structure and energetics of the interactive behavior of Li+ and Li with polycyclic aromatic hydrocarbons (PAHs) have been studied at the wB97XD/6-311G(d,p) level of DFT. The electron distribution in the PAHs, analyzed using the topology of the molecular electrostatic potential (MESP), led to the categorization of their aromatic rings into five types, viz Rs, Rn, Rd, Rb, and Re. Among the different rings, sextet-type Rs and naphthalene-type Rn rings showed the highest interaction with Li+. The change in MESP at the nucleus of Li+ (Delta VLi+) due to the formation of the complex Li+...PAH is found to be proportional to the adsorption energy (E1). In Li...PAH, the spin density on Li is close to zero, suggesting the formation of Li+...PAH center dot- due to the electron transfer from Li to PAH. The adsorption energy (E2) for Li...PAH does not correlate with the change in MESP at the nucleus of Li, whereas the dissociation energy (E3) of Li+...PAH center dot- to yield Li+ and PAH center dot- correlates well with the MESP data, Delta VLi. The study confirms that the change in MESP at the nucleus of Li+ due to complex formation gives a quantitative measure of the electronic effect of the cation-pi binding. The cell potential (Vcell) is predicted for the lithium ion battery (LIB) using the Li+...PAH and Li...PAH adsorption energies. On the basis of the Vcell data, "carbon nanoflake"-type systems, viz coronene, circumbiphenyl, C42H16, and C50H18 are suggested as good anode materials for LIBs.

The π-conjugation, aromaticity, and stability of the newly synthesized 12-infinitene and of other infinitenes comprising 8-, 10-, 14-, and 16-arene rings are investigated using density functional theory. The π-electron delocalization and aromatic character rooted in infinitenes are quantified in terms of molecular electrostatic potential (MESP) topology. Structurally, the infinitene bears a close resemblance of its helically twisted structure to the infinity symbol. The MESP topology shows that infinitene possesses an infinity-shaped delocalization of the electron density that streams over the fused benzenoid rings. The parameter ∑i=13Δλi, derived from the eigenvalues (λi) corresponding to the MESP minima, is used for quantifying the aromatic character of arene rings of infinitene. The structure, stability, and MESP topology features of 8-, 10-, 12-, 14-, and 16-infinitenes are also compared with the corresponding isomeric circulenes and carbon nanobelts. Further, the strain in all such systems is evaluated by considering the respective isomeric planar benzenoid hydrocarbons as reference systems. The 12-infinitene turns out to be the most aromatic and the least strained among all the systems examined.

ConspectusThe topology of molecular electrostatic potential (MESP), V(r), derived from a reliable quantum chemical method has been used as a powerful tool for the study of intermolecular noncovalent interactions. The MESP topology mapping is achieved by computing both ∇V(r) data and the elements of the Hessian matrix at ∇V(r) = 0, the critical point. MESP minimum (Vmin) as well as MESP at a reaction center, specific to an atom (Vn), have been employed as electronic parameters to interpret the variations in the reactivity (activation/deactivation) of chemical systems with respect to the influence of substituents, ligands, π-conjugation, aromaticity, trans influence, hybridization effects, steric effects, cooperativity, noncovalent interactions, etc. In this Account, several studies involving MESP topology analysis, which yielded interpretations of various noncovalent interactions and also provided new insights in the area of chemical bonding, are highlighted. The existence of lone pairs in molecules is distinctly reflected by the topology features of the MESP minima (Vmin). The Vmin is able to probe lone pairs in molecules, and it has been used as a reliable electronic parameter to assess their σ-donating power. Furthermore, MESP topology analysis can be used to forecast the structure and energetics of lone pair π-complexes. The MESP approach to rationalize lone pair interactions in molecular systems has led to the design of cyclic imines for CO2 capture. The MESP topology analysis of intermolecular complexes revealed a hitherto unknown phenomenon in chemical bonding theory─formation of a covalent bond due to the influence of a noncovalent bond. The MESP-guided approach to intermolecular interactions provided a successful design strategy for the development of CO2 capture systems. The MESP parameters Vmin and MESP at the nucleus, Vn, derived for the molecular systems have been used as powerful measures for the extent of electron donor-acceptor (eDA) interactions in noncovalent complexes. Noncovalent bond formation leads to more negative MESP at the acceptor nucleus (VnA) and less negative MESP at the donor nucleus (VnD). The strong linear relationship observed between ΔΔVn = ΔVnD - ΔVnA and bond energy suggested that MESP data provide a clear evidence of bond formation. Furthermore, MESP topology studies established a cooperativity rule for understanding the donor-acceptor interactive behavior of a dimer D...A with a third molecule. According to this, the electron reorganization in the dimer due to the eDA interaction enhances electron richness at "A", the acceptor, and enhances electron deficiency at "D", the donor. Resultantly, D in D...A is more accepting toward trimer formation, while A in D...A is more donating. MESP topology offers promising design strategies to tune the electron-donating strength in various noncovalent interactions in hydrogen-, dihydrogen-, halogen-, tetrel-, pnicogen-, chalcogen-, and aerogen-bonded complexes and thereby to predict the interactive behavior of molecules. To sum up, MESP topology analysis has become one of the most effective modern techniques for understanding, interpreting, and predicting the intermolecular interactive behavior of molecules.

Synthesis of core-modified 28 pi non-fused hexaphyrin is reported. The optical and 1H NMR spectral analysis reveals the non-aromatic nature of the macrocycle in its freebase form at 298 K. However, the non-aromatic nature of the macrocycle remains unaltered upon lowering the temperature. The structural elucidations for the freebase macrocycle also justify the non-aromaticity of the freebase 8, where the thiophene units of the 1,2 diphenyl 1,2 dithienyl ethene moiety is deviated maximum from the overall macrocyclic framework. Protonation on the imino pyrrolic nitrogens results in single-crystal X-ray structures of 8 which show essential distortion in macrocyclic framework needed for the effective pi-electron delocalization, attaining Mobius aromaticity. The Nucleus Independent Chemical Shift (NICS) values for the freebase and protonated macrocycles are -2.0 ppm and -5.6 ppm. The Anisotropy Induced Current density shows the clockwise delocalization of current density vectors. Overall, the spectral, structural and theoretical analysis suggests nonaromatic in freebase and Mobius aromatic nature of the protonated hexaphyrin. The synthesis of a 28 pi non-fused core-modified E-hexaphyrin is reported. An interesting transformation was observed, wherein the initially non-aromatic structure of the macrocycle was converted into an aromatic structure through the introduction of a proton to the imine nitrogen atoms.+image