Azomethine Carbon Research Articles

Theoretical interpretation of electron delocalization potential of the substituent in o-hydroxynaphthalidene-p-substituted anilines for prospective molecular electronics applications

The delocalization phenomenon plays a vital role in the electron transport properties of a molecule, which is essential for developing molecular-based electronics. The current work examined the delocalization potential of five theoretically designed low molecular weight anils, o-hyroxynaphthalidene-p-substitutedanilines(NP-X) with the substituent X(X = -CH3, -NO2, -OCH3, and –Cl) being placed in phenyl ring at the p- position to its functional moiety, azomethine linkage and compared with the compound without substitution(X = H). The geometric optimization through DFT with B3LYP/6-311G (d, p) level basis set indicated the anils to be coplanar. Theoretical FTIR could discriminate the aromatic and aliphatic C-H vibrational frequencies and confirm the vectorial flow of the electrons when the o-OH group and p-NO2 group were placed at the two extreme ends of anil, further supported by Natural Bond Orbital analysis. Atomic charge analysis indicated the significant effect on the charge of azomethine carbon atom. It followed the order: OCH3 < CH3 < H < Cl < NO2 parallel with the σp values of the corresponding substituent. The molecular electrostatic potential mapping identified azomethine nitrogen as an electron-rich centre. The global and local reactivity parameters indicated the highest tendency of NO2 substituted compound to accept electrons among the other compounds. The HOMO–LUMO energy gap of the NP-X predicted from Natural Localized Molecular Orbital analysis was found to be NP-H: 4.02 eV, NP-CH3: 3.94 eV, NP-NO2: 3.69 eV, NP-OCH3: 4.18 eV, NP-Cl: 4.10 eV. The overall studies corroborated the optimized delocalization in NP-NO2 with the lowest HUMO-LUMO gap, which would be better suited for developing molecular-based electronic devices than others. The importance of the electron delocalization phenomenon in searching for a molecular probe to develop molecular electronics device applications has been discussed.Graphical

α-Diazo-λ3-iodanes and α-diazo sulfonium salts: the umpolung of diazo compounds.

This minireview aims to cover the developments of the last few years in the design of reagents able to accomplish the umpolung of the azomethine carbon in diazo compounds namely, α-diazo-λ3-iodanes and α-diazo sulfonium salts. Specifically, the routes available for their preparation and a classification of their unique reactivity patterns (either acting as equivalents of carbene-radical or carbene-carbocation synthons) are discussed. We also present a detailed overview of the synthetic utility of such species and, when possible, a critical comparation their reactivity and properties.

Structural characterization, theoretical and antibacterial study of a V-shaped, cyclohexane bridged ONNO Schiff base

A tetradentate ONNO Schiff base bearing two chloro substituents, namely 6,6′-((1E,1′E)-(cyclohexane-1,2-diylbis(azanylylidene))bis(methanylylidene))bis(2-chlorophenol) (AD2C), was obtained through condensation of 3-chlorosalicyladehyde with 1,2-cyclohexanediamine. Structure elucidation was performed through physicochemical and spectroscopic analyses viz. melting point, elemental analysis, FTIR, 1H and 13C NMR, UV-Visible and single crystal X-ray diffraction. The ν(C=N) was observed at 1626 cm−1 while the azomethine proton and carbon chemical shifts appeared at 8.27 ppm and 157.56 ppm, respectively. The n‒π*(C=N) absorption band was observed at 324 nm. The crystal structure was stabilized by intramolecular hydrogen bond O˗H···N and intermolecular hydrogen bonds C˗H···O, C˗H···Cl, C˗H···π as well as π···π interactions. The existence of intermolecular interactions was confirmed through Hirshfeld analysis, showing high contribution of H⋯H contact. The B3LYP method was used to calculate the optimized structure of the molecule through density functional theory (DFT) using the 6–311++G(d, p) basis set and was found to be consistent with the X-ray diffraction value. The frontier molecular orbitals and molecular electrostatic potential of the compound investigated through DFT calculations revealed a significantly large energy gap of 4.615 eV and nucleophilic regions located at the hydroxyl groups. The compound showed no antibacterial activity against five bacterial strains namely Bacillus subtilis (ATCC 6633), Proteus vulgaris (ATCC 6380), Pseudomonas aeruginosa, Staphylococcus aureus subsp. aureus Rosenbach (ATCC 6538) and Streptococcus mutans Clarke (ATCC 700,610).

α‐Diazo Sulfonium Triflates: Synthesis, Structure, and Application to the Synthesis of 1‐(Dialkylamino)‐1,2,3‐triazoles

AbstractThe one‐pot synthesis of a series of sulfonium salts containing transferable diazomethyl groups is described, and the structure of these compounds is elucidated by X‐ray crystallography. Under photochemical conditions, reaction of these salts with N,N‐dialkyl hydrazones affords 1‐(dialkylamino)‐1,2,3‐triazoles via diazomethyl radical addition to the azomethine carbon followed by intramolecular ring closure. The straightforward transformation of the structures thus obtained into mesoionic carbene–metal complexes is also reported and the donor properties of these new ligands characterized.

α-Diazo Sulfonium Triflates: Synthesis, Structure, and Application to the Synthesis of 1-(Dialkylamino)-1,2,3-triazoles.

The one‐pot synthesis of a series of sulfonium salts containing transferable diazomethyl groups is described, and the structure of these compounds is elucidated by X‐ray crystallography. Under photochemical conditions, reaction of these salts with N,N‐dialkyl hydrazones affords 1‐(dialkylamino)‐1,2,3‐triazoles via diazomethyl radical addition to the azomethine carbon followed by intramolecular ring closure. The straightforward transformation of the structures thus obtained into mesoionic carbene–metal complexes is also reported and the donor properties of these new ligands characterized.

Synthesis, spectral studies and antibacterial activity of iron(III) complexes with hydrazone functionalized ligands: X-Ray structure determination of a novel five coordinate complex containing labile ligands

Iron(III) complexes having general formula FeLCl 2 [where, L = 2-acetylpyridine acetoylhydrazone(APAH), 2-acetylpyridine benzoylhydrazone(APBH), 2-acetylthiophene acetoylhydrazone(ATAH), and 2-acetythiophene benzoylhydrazone(ATBH) ] have been synthesized characterized based on molar conductivity, electronic and IR spectroscopy. The structure of iron(III) complex with APBH ligand is determined using single crystal X-Ray crystallography . The complex crystallizes in monoclinic space group P21/n with a = 7.8490(6) Å, b = 15.1018(11) Å, c = 13.2263(10) Å, α = 90°, β=100.183(3)°, γ = 90°, V = 1543.1(2) Å3 and Z = 4 with central Fe(III) ion coordinated one tridentate APBH ligand. The iron is 5- coordinate binding with one organic (hydrazone) unit and two labile chloride ligands. The hydrazone acts as NNO –tridentate donor system. Iron is coordinated by pyridine ring nitrogen, azomethine nitrogen and benzoyl oxygen atoms and the two chloride ligands bind with metal completing distorted square pyramidal structure. The iron complexes are screened for their anti-bacterial activities against Pseudomonas aureoginos and Bacillus cereus Acetoyl hydrazones show more antibacterial activity than the corresponding benzoyl hydrazones. Functional groups of azomethine carbon are varied. The hydrazones having a methyl/ and pyridine groups show more anti bacterial activity. The complexes show more activity than the ligands.

Two similar Schiff-base receptor based quinoline derivate: Highly selective fluorescent probe for Zn(II).

As is known, Zn2+ plays a vital role in a variety of biological processes but excessive exposure of Zn2+ to human beings can cause toxicity, inducing a series of overt poisoning symptoms and neurodegenerative disorders. Thus, we designed and synthesized two quinoline-derived Schiff-bases HL1 and HL2, and investigated the fluorescence emission responses of these two Schiff-bases to various metal ions. A significant enhancement in fluorescence emission band centered at 450nm was observed in the ethanolic solution of HL1 with addition of Zn2+, while remarkably lower fluorescence emission enhancement was obtained in the case of HL2 in which one methyl group was introduced to the azomethine carbon. In addition, HL1 showed good selectivity and high sensitivity towards Zn2+ in the existence of other various interfering metal ions, and the reversibility and regeneration of HL1 were also perfect for extending its applications in environmental and biological systems. Therefore, HL1 could be identified as a fluorescent probe for sensing Zn2+ environmentally and biologically.

Synthesis and Characterization of N-Benzylidene Aniline Ligand for Spectrophotometric Determination of Nickel

Schiff bases are compounds containing azomethine group (-HC=N-). They are condensation products of ketones or aldehydes (aldehydes and ketones) with primary amines. Formation of Schiff base generally takes place under acid or base catalysis or with heat. The spectrophotometric determination of metals using Schiff base metal complex is very important in analytical chemistry. This study has helped to establish a novel, simple and cheap analytical method for the determination of nickel in an environmental sample especially in developing countries where the cost and maintenance of sophisticated instruments are extremely high. In this study, Schiff base ligand was synthesized using benzaldehyde and aniline to form a metal complex with the target analyte (Ni 2+ ). The melting point and electrical conductivity of the synthesized nickel complex were 175.6 o C and 84x10 -6 Ώ -1 cm -1 respectively and the maximum absorbance at 360nm was 0.60. The complex was characterized using different spectroscopic techniques. The peak in FT-IR spectra at 1625.2 cm -1 confirmed the (C=N) stretching vibration. The 13 C and 1 H NMR spectra showed 193.8 and 10.0 ppm respectively of (CH=N) which was assigned to the azomethine carbon atom and the GC-MS analysis revealed a plausible structure of the complex. The stoichiometry of the Schiff base nickel (SB-Ni) complex was established as NiSB 2 by Job’s method of continuous variation, mole- ratio and slope-ratio methods. The three procedures are in agreement over the stoichiometry of the SB-Ni complex. Keywords : Complex, Stoichiometry, N-benzylideneaniline, Spectrophotometric, Ligand DOI : 10.7176/CMR/11-10-04 Publication date: December 31 st 2019

Synthesis, spectroscopic characterization, crystal structure, interaction with DNA, CTAB as well as evaluation of biological potency, docking and Molecular Dynamics studies of N-(3,4,5-trimethoxybenzylidene)-2, 3-dimethylbenzenamine

A novel N-substituted Schiff base ligand: N-(3,4,5-trimethoxybenzylidene)-2,3-dimethylbenzenamine was designed and successfully characterized by several spectroscopic techniques. The formation of the desired compound was confirmed by the appearance of CN peak at 1691 cm−1 in FT-IR spectrum. Similarly, in 1H and 13C NMR spectra, the peaks at 8.22 ppm for azomethine proton (HCN) and 158.8 ppm for azomethine carbon (CN) confirm the formation of the synthesized compound. DNA interaction of the compound was screened by using UV–visible spectroscopy and viscometry measurements confirming an intercalation mode. The interaction of compound with CTAB (Cetyl trimethylammonium bromide) was also studied by conductometric method showing a strong interaction with CTAB. The IC50 value of the current compound was highly efficacious upon comparison with the standard Glucantime used. This activity represents a higher multitude interaction, which might be a cause of enhanced antileishmanial activity. Cytotoxicity results showed that this compound is highly active even at lower concentrations and is biocompatible, making it a promising drug candidate for further investigations in this field. The experimental data were auxiliary supported by molecular docking studies in order to explore their binding behavior and the stability of the molecule due to its interaction within the receptor active site.

Synthesis, Spectroscopic Characterization and Biological Applications of Novel Zinc Complexes with Schiff Bases

Schiff base ligands, having nitrogen and oxygen donor sites and their zinc (II) complexes have been prepared by using methanol as a solvent. Purity of the compounds has been tested by TLC and are characterized by FT-IR, multinuclear NMR (1H and13C). FT-IR spectra suggested the binding of precursors and their chelation with zinc (II) moieties by showing characteristics peaks in particular regions.1H-NMR also approves the synthesis of compounds by showing characteristics peaks of azomethine proton (HC=N) and phenolic proton (-OH). On complexation phenolic proton was disappeared while a down field shift was observed in azomethine proton.13C-NMR data further supports the formation of compounds by the displaying and shifting of characteristic peaks of azomethine carbon (HC=N).The DNA binding ability of all the synthesized ligands was studied by UV-Visible spectroscopy. A hypochromic affect was observed showing that ligands interacted with DNA by intercalation. The results implied that these synthesized compounds can be employed for the formulation of Anticancer and Antitumor drugs in future with less toxic side effects to normal cells (unlike toxic drugs presently used) .Moreover they were found to have antifungal and antibacterial activity by Disc Diffusion method. Zinc containing complexes have been investigated a lot recently for the treatment of Diabetes Mellitus. Thus, these synthesized compounds are potential drug candidates for research if explored .

Radical‐Mediated Formal C(sp2)–H Functionalization of Aldehyde‐Derived N,N‐Dialkylhydrazones

Recent advances in formal C(sp2)–H functionalization of aldehyde‐derived N,N‐dialkylhydrazones (substitution at the azomethine carbon atom) are highlighted, with a focus on radical‐mediated processes that open up new opportunities for C–C bond formation, such as alkylation reactions with the aid of hypervalent iodonium reagents or polyhaloalkanes, as well as for carbon–heteroatom bond formation (C–N, C–P). Cascade sequences based on these reactions, and leading to (hetero)cyclic frameworks, are also discussed.

ChemInform Abstract: Electrophilic Trifluoromethylation of Carbonyl Compounds and Their Nitrogen Derivatives under Copper Catalysis

AbstractReview: [45 refs.

Toward an Understanding of the Ambiguous Electron Paramagnetic Resonance Spectra of the Iminoxy Radical from o-Fluorobenzaldehyde Oxime: Density Functional Theory and ab Initio Studies.

Iminoxy radicals (R1R2C═N—O•) possess an inherent ability to exist as E and Z isomers. Although isotropic hyperfine couplings for the species with R1 = H allow one to distinguish between E and Z, unequivocal assignment of the parameters observed in the EPR spectra of the radicals without the hydrogen atom at the azomethine carbon to the right isomer is not a simple task. The iminoxyl derived from o-fluoroacetophenone oxime (R1 = CH3 and R2 = o-FC6H5) appears to be a case in point. Moreover, for its two isomers the rotation of the o-FC6H5 group brings into existence the syn and anti conformers, depending on the mutual orientation of the F atom and C═N—O• group, making a description of hyperfine couplings to structure even more challenging. To accomplish this, a vast array of theoretical methods (DFT, OO-SCS-MP2, QCISD) was used to calculate the isotropic hyperfine couplings. The comparison between experimental and theoretical values revealed that the E isomer is the dominant radical form, for which a fast interconversion between anti and syn conformers is expected. In addition, the origin of the significant AF increase with solvent polarity was analyzed.

Synthesis of Potentially Antioxidant and Antibacterial Biologically Active Thiazolidines

In 3–5 h at 60–80ºC in pyridine, thiosemicarbazones reacted with 2-arylidenemalononitriles to afford arylidenehydrazono-4-aryl-2,3-dihydrothiazole-5-carbonitriles. On repeating the same reaction in a domestic microwave oven with a few drops of pyridine, the reaction proceeded in 5–10 min to produce the same dihydrothiazole products in nearly quantitative yields. The structures of the products were elucidated via NMR, IR, and mass spectra and elemental analyses. Antibacterial activities (against Gram-positive and Gram-negative bacteria) and antioxidant activities were tested. A thiazolidine having a pyridyl group connected to the azomethine carbon, (E)-5-phenyl-2-((E)-(1-(pyridin-2-yl)ethylidene)-hydrazono)-2,3-dihydrothiazole-4-carbonitrile showed high antioxidant and antibacterial activities. A promising antioxidant activity was also noted in the starting thiosemicarbazones. The structure–activity relationship was investigated.

Linear Free‐Energy Relationships Applied to the 13C NMR Chemical Shifts in 4‐Substituted N‐[1‐(Pyridine‐3‐ and ‐4‐yl)ethylidene]anilines

Two series of 4‐substituted N‐[1‐(pyridine‐3‐ and ‐4‐yl)ethylidene]anilines have been synthesized using different methods of conventional and microwave‐assisted synthesis, and linear free‐energy relationships have been applied to the 13C NMR chemical shifts of the carbon atoms of interest. The substituent‐induced chemical shifts have been analyzed using single substituent parameter and dual substituent parameter methods. The presented correlations describe satisfactorily the field and resonance substituent effects having similar contributions for C1 and the azomethine carbon, with exception of the carbon atom in para position to the substituent X. In both series, negative ρ values have been found for C1′ atom (reverse substituent effect). Quantum chemical calculations of the optimized geometries at MP2/6‐31G++(d,p) level, together with 13C NMR chemical shifts, give a better insight into the influence of the molecular conformation on the transmission of electronic substituent effects. The comparison of correlation results for different series of imines with phenyl, 4‐nitrophenyl, 2‐pyridyl, 3‐pyridyl, 4‐pyridyl group attached at the azomethine carbon with the results for 4‐substituted N‐[1‐(pyridine‐3‐ and ‐4‐yl)ethylidene]anilines for the same substituent set (X) indicates that a combination of the influences of electronic effects of the substituent X and the π1‐unit can be described as a sensitive balance of different resonance structures.

4-HYDROXY-2-QUINOLONES. 203. REACTION OF 1-HEXYL- 4-HYDROXY-2-OXO-1,2-DIHYDROQUINOLINE-3-CARBOXYLIC ACID 4-PYRIDYLMETHYLIDENE HYDRAZIDE WITH BROMINE

It has been shown experimentally that upon the reaction of 1-hexyl-4-hydroxy-2-oxo-1,2-dihydro-quinoline-3-carboxylic acid 4-pyridylmethylidene hydrazide with molecular bromine in glacial acetic acid not only the azomethine carbon atom is brominated, but also the position 6 of the quinolone ring. Authors: I. V. Ukrainets, E. V. Mospanova, and S. V. Shishkina English Translation in Chemistry of Heterocyclic Compounds , 2012, 48 (8), pp 1200-1203 http://link.springer.com/article/10.1007/s10593-012-1122-z

4-hydroxy-2-quinolones. 203*. Reaction of 1-hexyl-4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acid 4-pyridylmethylidene hydrazide with bromine

It has been shown experimentally that upon the reaction of 1-hexyl-4-hydroxy-2-oxo-1,2-dihydroquinoline-3-carboxylic acid 4-pyridylmethylidene hydrazide with molecular bromine in glacial acetic acid not only the azomethine carbon atom is brominated, but also the position 6 of the quinolone ring.

Organometallic ruthenium(II) complexes: Synthesis, structure and influence of substitution at azomethine carbon towards DNA/BSA binding, radical scavenging and cytotoxicity

Bivalent, ruthenium organometallics containing hydrazone ligands with the composition [RuH(CO)(PPh3)2(L1−3)] (4–6) have been synthesised from the reactions of [RuH2(CO)(PPh3)3] and benzoic acid pyridine-2-ylmethylene-hydrazide (HL1) (1) /benzoic acid (1-pyridin-2-yl-ethylidene)-hydrazide (HL2) (2)/benzoic acid (phenyl-pyridin-2-yl-methylene)-hydrazide (HL3) (3) and characterised by various physico–chemical techniques. The X-ray crystal structure of one of the above complexes, [RuH(CO)(PPh3)2(L3)] (6) demonstrated a distorted octahedral coordination geometry around the metal centre. Results of our investigation on the effect of substitution (H or CH3 or C6H5) at the azomethine carbon of coordinated hydrazone in these ruthenium chelates on the potential binding with DNA/BSA, free radical scavenging and cytotoxicity is presented.

ChemInform Abstract: 1,3‐Dipolar Cycloaddition Reactions of 2‐Substituted Azomethine N‐Oxides with N‐Benzyl Maleimides Leading to the Synthesis of Stereoisomers.

AbstractAzomethine N‐oxides (I) and (V) react with N‐benzylmaleimide (II) to provide a mixture of stereoisomers having cis (III), (VII) and trans (IV), (VI) configurations with respect to the proton on the C‐3 azomethine carbon.

The substituent effects on the 13c chemical shifts of the azomethine carbon atom of n-(phenyl substituted) salycilaldimines

The Hammett correlations between 13C-NMR chemical shifts of the azomethine carbon atom and the corresponding substituent constants for thirtheen Schiff bases were established. Successful correlation of the chemical shifts with electrophilic substituent constants ?+ indicate significant resonance interaction of the substituents on the aniline ring with the azomethine carbon atom in the examined series of imines. The demand for electrons in the investigated compounds was compared to that of the N-benzylidenanilines and N-(phenyl substituted) pyridinealdimines. The way of transmission of the substituent effects was discussed and they are separated into resonance and inductive effects. Inductive effects prevail over resonance effects.