Relative Nucleophilicity Research Articles

Syntheses, DFT studies and comparatively photovoltaic applications of some pyrene-imine hybrid derivatives

In this study, (E)-N-phenyl-1(pyren-1yl)methanimine (3) and a isomeric mixture of 5ZZ and 5EE (1,4-phenylenebis(1-(pyren-1-yl)methanimine) were synthesized by condensation of pyrene-1-carbaldehyde (1) with aniline (2) or benzene-1,4-diamine (4) The synthesized compounds were characterized using NMR, UV–vis, IR and HRMS spectroscopic techniques.Utilizing the density functional theory (DFT) and a basis set of B3LYP/6-311G(2d,2p), theoretical computations were done. The computed values were applied to simulated spectra of compounds 3 and the isomeric mixtures 5EE, and 5ZZ demonstrating good agreement with observed spectra. In various solvents, the UV–vis spectra of compounds 3, 5EE, and 5ZZ were recorded in areas 200–500 nm, and function density theory (DFT) and time-dependent density functional theory (TD-DFT) algorithms were used to determine if they can serve as metal-free organic dyes in the use of dye-sensitized solar cells (DSSCs). The charge separation distance (Δr) between an electron and the hole it corresponds to was investigated in addition to the degree of electron-hole overlap (Λ) because transition density matrices (TDM) give information about how each electron departs from its corresponding hole during excitations, resulting in charge transfer (CT). To obtain more insight into the characteristics of complexes, the Mulliken population approach, density of states (TDOS), natural population analysis (NPA), molecular electrostatic potential (MEP), condensed Fukui function, and relative nucleophilicity indices derived from orbital charge calculation results (NPA) were used. In addition, the photovoltaic properties of these compounds were studied comparatively. DFT band gap for 3 was 2.493, 5EE was 2.050, and 5ZZ was 2.071 eV. Furthermore, the power conversion efficiency (PCE) values for compound 3 and the isomeric mixture of compound 5 are calculated as 2.31%, and 2.82%, respectively. The results obtained can provide a useful reference for the development of organic compounds containing pyrene units in more efficient organic-based compounds for photovoltaic applications.

Property and reactivity of polyselenides and polysulfides: a quantum chemistry study

High-level ab initio and density functional theory were applied to investigate property and reactivity of polyselenides and polysulfides. With CH3XnH (X = S or Se) we found that the deprotonation energy (and pKa ) of CH3SenH, ionization potential (IP) of , and CH3Sen−H bond dissociation energy (BDE) are lower than those of their sulfur counterparts. For n = 2, IPs and X−H BDEs are exceptionally small. The relative nucleophilicity of vary with substrates. However, CH3SenH are more nucleophilic than CH3SnH due to their due to their lower deprotonation energy. The nucleophilicity of selenolates versus thiolates are related to the chemical nature. Selenium is more electrophilic than sulfur.

Regioselectivity in the reaction of 5-amino-3-anilino-1H-pyrazole-4-carbonitrile with cinnamonitriles and enaminones: Synthesis of functionally substituted pyrazolo[1,5-a]pyrimidine derivatives

Abstract The development of efficient methods for the synthesis of polyfunctional N-heterocycles is an important area of research in organic and medicinal chemistry. Pyrazolo[1,5-a]pyrimidine derivatives are purine analogous of biomedical importance and have been extremely studied for their broad spectrum of biological activities. Recently, they have attracted great interest in materials science owing to their photophysical properties. 3(5)-Aminopyrazoles are extensively utilized in the synthesis of condensed heterocyclic systems, particularly pyrazolo[1,5-a]pyrimidines via the reaction with 1,3-biselectrophilic reagents. However, the information available in the literature provides little in the way of reasoning their cyclization, particularly the initial attack either by the exocyclic amino group or endocyclic nitrogen. Unfortunately, the relative nucleophilicity of exo- and endocyclic nitrogen atoms in 1-unsubstituted 3(5)-aminopyrazoles is not clear and contradicting. It has been found that other factors can modulate the regioselectivity rather than basicity or steric hindrance for both active sites. The reported studies in the structure–activity relationship revealed that pyrazolo[1,5-a]pyrimidines having a substitution at fifth, sixth, and seventh positions possess potent biological activities, especially those with an amino group at the seventh position. We here developed a regioselective, high yield synthesis of 7-amino-5-arylpyrazolo[1,5-a]pyrimidine-3,6-dicarbonitriles by the reaction of N-(5-amino-4-cyano-1H-pyrazole-3-yl)-benzamide with various cinnamonitriles and enaminones in pyridine at 120°C under controlled microwave heating conditions. All structures of newly synthesized compounds were established by analytical and spectral data as well as single-crystal diffraction and rationalized for their formation.

Computational study for the electrophilic reactivity prediction of crown ethers

Crown ethers are kinds of macrocyclic compounds with high selectivity to metal cations, which can be used as ion sensors, ion analytical reagents and ionophores for biological applications. The chemical reactivity of 1,8-dihydroxyl-4,4,5,5-tetramethylbenzo-14-crown-4 had been investigated at the level of M062X/def2TZVP with Gauss16. The conformations were studied though the high-temperature annealing process with Gromacs. The applicability of Frontier molecular orbital theory, Conceptual density functional theory and Molecular electrostatic potential analysis for the reactivity prediction were discussed. The analysis results show that the methods reflecting the electronic softness property such as Fukui function, global softness, relative nucleophilicity, are suitable for the prediction of electrophilic substitution reaction sites. The electrophilic substitution reaction sites of different conformations are at the C25 or C26 atom, which has the largest HOMO orbital compositions. The oxygen atoms of the main ring and the hydroxyl groups are the binding sites of metal cations. The lowest electrostatic potential is −74.81 kcal/mol on the vdW surface of (1R, 8S) 1,8-dihydroxyl-4,4,5,5-tetramethylbenzo-14-crown-4 contributing to the lone pair electrons and π-electron cloud. The hydroxyl groups and the benzene ring can decrease the surface potential and increase the reactivity.

Preparation of (mono)sulfonates: Suitable precursors for unnatural sulfonolipids

Aiming at the preparation of the novel unnatural, non-isosteric sulfonolipids bearing one, two and three acyl groups 8, 9 and 10, their precursors hydroxyl-containing sulfonates have been prepared from a variety of hydroxyl-containing halogenides and epoxides using the Strecker reaction. Thus, the sulfonates 16 and 22 were prepared pure, while the sulfonate 27 could only be prepared as a by-product using 1,4-dibromo-2,3-butanediol 26 and in low yields. For these reactions, probable pathways leading to the isolated or spectroscopically identified products are proposed. Conclusions about the relative nucleophilicity of SO32- compared to AsO33 - (as well as HO- which is present in their aqueous solutions) were drawn based on the yields of the corresponding arsonic acids and sodium sulfonates. The IR (KBr) and 1H NMR (D2O) spectra of sulfonates (and in some cases of their sulfonic acids) are analyzed and discussed.

Preferential Sites for Adsorption of CO on Au6 Clusters Using Density Functional Theory Based Reactivity Descriptors.

Nanoarchitectonics of neutral Au6 cluster upon addition and removal of one electron have been studied using density functional based reactivity descriptors. We studied the response of various sites of cationic, neutral and anionic Au6 clusters towards impending electrophilic and nucleophilic attacks using DFT based local reactivity descriptors, viz, Fukui function for nucleophilic attack f+. Fukui function for electrophilic attack f-, relative nucleophilicity f+/f- and relative electrophilicity f+/f-. Based on these parameters different types of unique atoms have been identified for each cluster. Reactivity predictions for the unique atoms of the minimum energy planar triangular Au6 structure have been verified by using CO as a probe molecule. It has been found adsorption of CO molecules on gold cluster brings about structural changes in the cluster and that the CO molecule prefers the apex site for adsorption onto the triangular Au6 cluster as compared to the mid site.

High-Performance Phase-Pure SnS Photocathodes for Photoelectrochemical Water Splitting Obtained via Molecular Ink-Derived Seed-Assisted Growth of Nanoplates.

Although tin monosulfide (SnS) is one of the promising earth-abundant semiconducting materials for photoelectrochemical water splitting, the performance of SnS photocathodes remains poor. Herein, we report a stepwise approach for the fabrication of highly efficient photocathodes based on SnS nanoplates via elaborate modulation of molecular solutions. It is demonstrated that phase-pure SnS nanoplates without detrimental secondary phases (such as SnS2 and Sn2S3) can be readily obtained by adjusting the amounts of Sn and S in the precursor solution. Additionally, the orientation of SnS nanoplates is controlled by implementing different types of SnS seed layers. The orientations of the SnS seed layers are changed according to the molecular shapes of the Sn-S bonds in the molecular solutions, depending on the relative nucleophilicity of the molecular moieties formed by specific thiol-amine reactions. The molecular Sn-S sheets in the seed ink was obtained by the reaction in a solvent mixture of thiogylcolic acid and ethanolamine. By contrast, the short Sn-S molecular rods result from the reaction in a solvent mixture of 2-mercaptoethanol and ethylenediamine. Interestingly, the relatively short rodlike morphology of the SnS seed induces the growth of SnS nanostructures faceted by preferred (111) and (101) planes, leading to fast charge transport. With the formation of a proper band alignment with n-type CdS and TiO2, the preferred (111)- and (101)-oriented SnS nanoplate-based photocathode exhibited a photocurrent density of -19 mA cm-2 at 0 V versus a reversible hydrogen electrode, establishing a new benchmark for SnS photocathodes.

Pd-Catalyzed C-N Coupling Reactions Facilitated by Organic Bases: Mechanistic Investigation Leads to Enhanced Reactivity in the Arylation of Weakly Binding Amines.

The ability to use soluble organic amine bases in Pd-catalyzed C-N cross-coupling reactions has provided a long-awaited solution to the many issues associated with employing traditional, heterogeneous reaction conditions. However, little is known about the precise function of these bases in the catalytic cycle and about the effect of variations in base structure on catalyst reactivity. We used 19F NMR to analyze the kinetic behavior of C-N coupling reactions facilitated by different organic bases. In the case of aniline coupling reactions employing DBU, the resting state was a DBU-bound oxidative addition complex, LPd(DBU)(Ar)X, and the reaction was found to be inhibited by base. In general, however, depending on the binding properties of the chosen organic base, increased concentration of the base can have a positive or negative influence on the reaction rate. Furthermore, the electronic nature of the aryl triflate employed in the reaction directly affects the reaction rate. The fastest reaction rates were observed with electronically neutral aryl triflates, while the slowest were observed with highly electron-rich and -deficient substrates. We propose a model in which the turnover-limiting step of the catalytic cycle depends on the relative nucleophilicity of the base compared to that of the amine. This hypothesis guided the discovery of new reaction conditions for the coupling of weakly binding amines, including secondary aryl amines, which were unreactive nucleophiles in our original protocol.

X-ray and DFT Investigation of (E)-4-bromo-5-methoxy-2-((o-tolylimino)methyl)phenol Compound

(E)-4-bromo-5-methoxy-2-((o-tolylimino)methyl)phenol was investigated by experimental and theoretical methodologies. The solid state molecular structure was determined by X-ray diffraction method. All theoretical calculations were performed by density functional theory (DFT) method by using B3LYP/6-31G(d,p) basis set. The titled compound showed the preference of enol form, as supported by X-ray diffraction method. The geometric and molecular properties were compaired for both enol-imine and keto-amine forms for title compound. Stability of the molecule arises from hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond has been analyzed using natural bond orbital (NBO) analysis. Mulliken population method and natural population analysis (NPA) have been studied. Also, condensed Fukui function and relative nucleophilicity indices calculated from charges obtained with orbital charge calculation methods (NPA). Molecular electrostatic potential (MEP) and non linear optical (NLO) properties are also examined.

Synthesis of α-Thiooximes by Addition of Thiols to N,N-Bis(oxy)-enamines: A Comparative Study of S-, N-, and O-Nucleo­philes in Michael Reaction with Nitrosoalkene Species

Nucleophilic addition of thiols to N,N-bis(oxy)enamines (nitrosoalkene acetals) produce valuable α-thiooximes in a highly efficient manner. The reaction was found to be solvent-dependent, likely because of distinct mechanisms operating in nonpolar and basic solvents (involving either Brønsted acid or Lewis base catalysis). By performing a series of competition experiments, the relative reactivity of S-, N-, and O-nucleophiles in reaction with N,N-bis(oxy)enamines was determined for the first time. Interestingly, the relative nucleophilicity was found to be highly dependent on the solvent, which allows regioselective control of these reactions by using an appropriate medium.

Formation of Carbamate Anions by the Gas-phase Reaction of Anilide Ions with CO2.

The anilide anion (m/z 92) generated directly from aniline, or indirectly as a fragmentation product of deprotonated acetanilide, captures CO2 readily to form the carbamate anion (m/z 136) in the collision cell, when CO2 is used as the collision gas in a tandem-quadrupole mass spectrometer. The gas-phase affinity of the anilide ion to CO2 is significantly higher than that of the phenoxide anion (m/z 93), which adds to CO2 only very sluggishly. Our results suggest that the efficacy of CO2 capture depends on the natural charge density on the nitrogen atom, and relative nucleophilicity of the anilide anion. Generally, conjugate bases generated from aniline derivatives with proton affinities (PA) less than 350 kcal/mol do not tend to add CO2 to form gaseous carbamate ions. For example, the anion generated from p-methoxyaniline (PA = 367 kcal/mol) reacts significantly faster than that obtained from p-nitroaniline (PA = 343 kcal/mol). Although deprotonated p-aminobenzoic acid adds very poorly because the negative charge is now located primarily on the carboxylate group, it reacts more efficiently with CO2 if the carboxyl group is esterified. Moreover, mixture of CO2 and He as the collision gas was found to afford more efficient adduct formation than CO2 alone, or as mixtures made with nitrogen or argon, because helium acts as an effective "cooling" gas and reduces the internal energy of reactant ions.

The spectroscopic (FT-IR, UV–vis), Fukui function, NLO, NBO, NPA and tautomerism effect analysis of (E)-2-[(2-hydroxy-6-methoxybenzylidene)amino]benzonitrile

A new o-hydroxy Schiff base, (E)-2-[(2-hydroxy-6-methoxybenzylidene)amino]benzonitrile was isolated and investigated by experimental and theoretical methodologies. The solid state molecular structure was determined by X-ray diffraction method. The vibrational spectral analysis was carried out by using FT-IR spectroscopy in the range of 4000–400cm−1. Theoretical calculations were performed by density functional theory (DFT) method using 6-31G(d,p) basis set. The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The UV–vis spectrum of the compound was recorded in the region 200–800nm in several solvents and electronic properties such as excitation energies, and wavelengths were calculated by TD-DFT/B3LYP method. The most prominent transitions were corresponds to π→π∗.Hybrid density functional theory (DFT) was used to investigate the enol-imine and keto-amine tautomers of titled compound. The titled compound showed the preference of enol form, as supported by X-ray and spectroscopic analysis results. The geometric and molecular properties were compaired for both enol-imine and keto-amine forms. Additionally, geometry optimizations in solvent media were performed with the same level of theory by the integral equation formalism polarizable continuum (IEF-PCM). Stability of the molecule arises from hyperconjugative interactions, charge delocalization and intramolecular hydrogen bond has been analyzed using natural bond orbital (NBO) analysis. Mulliken population method and natural population analysis (NPA) have been studied. Also, condensed Fukui function and relative nucleophilicity indices calculated from charges obtained with orbital charge calculation methods (NPA). Molecular electrostatic potential (MEP) and non linear optical (NLO) properties are also examined.

Synthesis and characterization of heterobimetallic complexes with direct Cu-M bonds (M = Cr, Mn, Co, Mo, Ru, W) supported by N-heterocyclic carbene ligands: a toolkit for catalytic reaction discovery.

Building upon the precedent of catalytically active (NHC)Cu-FeCp(CO)2 complexes, a series of (NHC)Cu-[M] complexes were synthesized via the addition of Na(+)[M](-) reagents to (NHC)CuCl synthons. The different [M](-) anions used span a range of 7 × 10(7) relative nucleophilicity units, allowing for controlled variation of nucleophile/electrophile pairing in the heterobimetallic species. Direct Cu-M bonds (M = Cr, Mn, Co, Mo, Ru, W) formed readily when the bulky IPr carbene was used as a support. Crystallographic characterization and computational examination of these complexes was conducted. For the smaller IMes carbene, structural isomerism was observed when using the weakest [M](-) nucleophiles, with (IMes)Cu-[M] and {(IMes)2Cu}{Cu[M]2} isomers being observed in equilibrium. Collectively, the series of complexes provides a toolbox for catalytic reaction discovery with precise control of structure-function relationships.

Experimental and Theoretical Investigations on the Corrosion Inhibition of Lumazine over Mild Steel in 1M HCl

The corrosion inhibition efficiencies and adsorption characteristics of Lumazine over mild steel in 1 M HCl were investigated using electrochemical and theoretical methods. The Gravimetric and electrochemical methods used in the present investigation includes weight loss, Tafel polarisation and Electrochemical Impedance Spectroscopy methods respectively. The adsorption studies carried out using this inhibitor adhere to Langmuir adsorption isotherm. In addition, the equilibrium constant and free energy of adsorption were calculated for the inhibitors on mild steel in 1 M HCl. Density Functional Theory using B3LYP functional was utilised to calculate the quantum chemical parameters of the inhibitors which were used to determine their contribution to inhibition of corrosion. HOMO LUMO, mulliken atomic charge, condensed fukui functions, local softness, relative nucleophilicity and relative electrophilicity were analysed to study the possible site of the inhibitor molecule at the metal surface. The quantitative structure-activity relationship (QSAR) has been established to correlate the experimental inhibition efficiencies and the quantum chemical parameters to model mathematical equations describing theoretical inhibition efficiencies.

End-Group Cleavage in MALDI of ATRP-Made Polystyrene: A Silver-Catalyzed Reaction during Sample Preparation

Cleavage of the labile halide termination upon matrix-assisted laser desorption/ionization (MALDI) has always been reported as a major concern in mass analysis of polystyrene prepared by atom transfer radical polymerization (ATRP). By studying this issue using nuclear magnetic resonance (NMR) and electrospray ionization-mass spectrometry, we evidence here that the ionization step is not involved in this deleterious process. Instead, removal of the halogen was shown to readily occur upon interaction of the silver salt (AgTFA) used as the cationizing agent in mass spectrometry, either in solution or in the solid-state when performing solvent-free sample preparation. In solution, this silver-induced reaction mostly consists of a nucleophilic substitution, leading to polystyrene molecules holding different terminations, depending on relative nucleophilicity of species present in the liquid-phase solution composition. In chloroform supplemented with AgTFA, trifluoroacetate-terminated PS were evidenced in ESI-MS spectra but experienced end-group cleavage in MALDI. In contrast, the major methoxy-terminated PS macromolecules formed when the silver-catalyzed nucleophilic substitution was performed in methanol were generated as intact gas-phase ions using both ionization techniques. This controlled and fast modification could hence be advantageously used as a rapid sample pretreatment for safe MALDI mass analysis of ATRP-made polystyrene.

Exploring structures, electronic and reactivity properties of Au6Hn (n = 1–12) clusters: A DFT approach

Density functional calculations at the PBE/DNP level have been carried out to investigate the structures, electronic and reactivity properties of Au6Hn (n=1–12) clusters. Adsorption of hydrogen atoms stabilizes the Au6 cluster indicated by the high binding energies. The adsorption of H atoms till Au6H6 retains the planar triangular structure of Au6. However, the triangular structure is distorted on further addition of H atoms till Au6H9. In clusters Au6H10, Au6H11 and Au6H12, though the triangular structure is restored but the structures are non-planar. The averaged Hirshfeld atomic charges indicate the H atoms to be negatively charged in all the clusters. Odd–even alternation in HOMO–LUMO gap, chemical hardness, vertical ionization potential, adiabatic ionization potential and binding energy is observed with the clusters having even number of H atoms possessing higher values and are observed to be more stable than their congeners with odd number of H atoms. DFT based reactivity descriptors indicate that in Au6, the Au atoms forming the vertices of the outer triangle have higher relative electrophilicity value while those forming the vertices of the inner triangle have higher relative nucleophilicity value. However, in Au6H6, two nearby Au sites forming the vertices of the inner and outer triangle have the highest relative electrophilicity and relative nucleophilicity values. In Au6H12, these are located in the inner triangle.

A computational study on conformational geometries, chemical reactivity and inhibitor property of an alkaloid bicuculline with γ-aminobutyric acid (GABA) by DFT

Bicuculline – a plant alkaloid is an important molecule of current pharmaceutical interest. It is a competitive antagonist of γ-aminobutyric acid (GABA), particularly of GABAA receptor activation. The antagonistic behavior of BIC with GABAA receptor has been evaluated with the help of quantum chemical calculations. The equilibrium structures of bicuculline conformers have been obtained by geometry optimizations using density functional theory (DFT) calculations at the B3LYP/6-311G(d,p) level of theory. The conformational flexibility of bicuculline has been investigated because of its importance as an apparently specific antagonist of the neurotransmitter GABA. Dipole moment and first hyperpolarizability analysis of BIC have also been performed. For predicting inhibitor properties of BIC, the specific site of interaction of BIC with GABA receptor has been calculated with the help of global and local reactivity descriptors using DFT. Condensed Fukui functions, relative nucleophilicity and electrophilicity indices of BIC and GABA receptor for electrophilic or nucleophilic attack, are computed and compared with the HOMO and LUMO densities, integrated over the Hirshfeld atoms in molecules.

Relationship between local reactivity indices and the hammett constant for isatoic anhydride and its derivatives

AbstractLocal reactivity is obtained for isatoic anhydride (ISA) (2H 3,1‐benzoxazin‐2,4(1H)‐dione) and 20 of its derivatives, using reactivity indices such as: local softness, condensed Fukui function, relative electrophilicity index, and relative nucleophilicity index. The local reactivity results for ISA show the best sites for a nucleophilic attack and for an electrophilic attack. A linear model is proposed from statistical methods to describe the substituent effect for the relationship between gas phase reactivity indices with respect to the Hammett constant values. © 2012 Wiley Periodicals, Inc.

Open and capped (5,5) armchair SWCNTs: A comparative study of DFT-based reactivity descriptors

Density functional theory (DFT) calculations have been performed to predict the reactivity pattern governing the nucleophilic, electrophilic and radical attacks on the external surface of open and capped (5,5) armchair single-walled carbon nanotubes (SWCNTs). The DFT-based local reactivity descriptors, viz, Fukui function, local softness, relative electrophilicity, relative nucleophilicity and dual reactivity descriptor, have been examined for predicting the reactivity of different carbon atom sites of the considered SWCNTs. The predictions of regioselectivity using relative electrophilicity, relative nucleophilicity and dual reactivity descriptors have been verified by reaction energies calculated for model systems at the M06-2X/6-31G(d) level.

A versatile method for functionalizing surfaces with bioactive glycans.

Microarrays and biosensors owe their functionality to our ability to display surface-bound biomolecules with retained biological function. Versatile, stable, and facile methods for the immobilization of bioactive compounds on surfaces have expanded the application of high-throughput "omics"-scale screening of molecular interactions by nonexpert laboratories. Herein, we demonstrate the potential of simplified chemistries to fabricate a glycan microarray, utilizing divinyl sulfone (DVS)-modified surfaces for the covalent immobilization of natural and chemically derived carbohydrates, as well as glycoproteins. The bioactivity of the captured glycans was quantitatively examined by surface plasmon resonance imaging (SPRi). Composition and spectroscopic evidence of carbohydrate species on the DVS-modified surface were obtained by X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), respectively. The site-selective immobilization of glycans based on relative nucleophilicity (reducing sugar vs amine- and sulfhydryl-derived saccharides) and anomeric configuration was also examined. Our results demonstrate straightforward and reproducible conjugation of a variety of functional biomolecules onto a vinyl sulfone-modified biosensor surface. The simplicity of this method will have a significant impact on glycomics research, as it expands the ability of nonsynthetic laboratories to rapidly construct functional glycan microarrays and quantitative biosensors.