Computational thermochemistry of C-nitroso compounds

The molecular structure and thermodynamic stability of C-nitroso and dinitroso (azodioxide) compounds (CNC) have been studied by using high-level, composite, ab initio method (G4MP2) via the series of appropriate homodesmotic, dimerization reactions. The calculated reaction enthalpies and Gibbs free energies allowed us to estimate relative stability of dinitroso moiety and the role of substituents in thermodynamic stabilization of dinitroso group versus its monomeric precursor. The stability of dinitroso compounds is generally low as is indicated by large positive values for standard enthalpies of formation. The stabilization of the dinitroso group is much more pronounced in alkyl, alkenyl, or alkynyl derivatives than in the aromatic derivatives. The thermodynamic stability of E-stereoisomers of dinitroso compounds is generally larger than their Z-stereoisomer analogues. However, the difference in E/Z stereoisomer stability is quite small in aromatic dinitroso compounds. We have discussed the influence of substituents on the molecular geometry of the nitroso and dinitroso groups. We have also discussed the nature and strengths of solid-state forces pertaining to CNC.     

Application of HSQC in the delineation of NMR signals of E and Z isomers of octadecyl p‐coumarates

Octadecyl p‐coumarates undergo E–Z isomerization in daylight. Although ¹H NMR, ¹³C NMR and ¹H–¹H COSY gave indications about this isomerization, the overlapping of some signals in the ¹H NMR of aromatic region prevented the delineation of signals of the individual isomers. However, heteronuclear spin quantum coupling correlation (HSQC) with the unique feature of two sets of nearby δ_C–δ_H correlations gave conclusive evidence for this isomerization and helped in the delineation of ¹H NMR and ¹³C NMR signals of E‐octadecyl p‐coumarate and Z‐octadecyl p‐coumarate. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis,Structure, and Biological Activity of (2Z)-2-[(2,4-Dinitrophenyl)hydrazinylidene]butanedioic Acid Esters

Dialkyl (2Z)-2-[(2,4-dinitrophenyl)hydrazinylidene]butanedioates have been synthesized by reaction of dialkyl (2Z)-2-hydroxybut-2-enedioates with 2,4-dinitrophenylhydrazine, and their structure has been studied by IR and ¹H NMR spectroscopy, mass spectrometry, and X-ray analysis.

     

A new intramolecular transformation of aromatic nitroso oxides

The possibility of intramolecular interaction of a nitroso oxide group with an aromatic ring is investigated at the UB3LYP/6-311+G(d,p) and G3MP2B3 levels of theory for a wide series of aromatic nitroso oxides. It is found that this reaction leads to the formation of a dioxazole cycle, its subsequent decay resulting in opening of the benzene ring and formation of nitriloxide and carbonyl functional groups. The activation enthalpy of the transformation of phenylnitroso oxide is 75.1 kJ/mol. It is shown that various sub-stituents at ortho-position (with respect to the nitroso oxide fragment) considerably lower the activation barrier of the investigated transformation, particularly in case of o,p-dimethoxyphenylnitroso oxide ΔH ^≠ = 43.7 kJ/mol. It is concluded that in the case of polyaromatic nitroso oxides, for which intramolecular cyclization is more typical (ΔH ^≠ ∼ 50 kJ/mol), a factor favoring the attack on the ortho-carbon atom is the stabilization of the product’s diene group due to its inclusion in the polyaromatic system. It is established that sum of these effects leads to a low activation barrier for the transformation of nitroso oxide that forms during the photooxidizing of 2-azido-1-methoxyphenazine, ΔH ^≠ = 19 kJ/mol. It is proposed that due to the low activation energy of some nitroso oxides, their intramolecular cyclization may be the primary channel of their unimolecular decay.     

13C and 1H NMR investigation of the structure of N″-sulphonyl-N-alkylideneformamidrazones

The ¹³C and ¹H NMR spectra of N″-sulphonyl-N-alkylideneformamidrazones have been recorded and the chemical shifts assigned. The tautomeric structure proved to be an N²- alkylidenehydrazide sulphonylimide. The barrier to rotation around the CN¹ bond was estimated from variable from temperature ¹H NMR measurements, and the Z/E ratio and its solvent dependence was investigated.     

Intermolecular steric hindrance in 7-acylamino-[1H]-2-oxo-1,8-naphthyridines: NMR,ESI-MS,IR, and DFT calculation studies

Abstract  

Intermolecular interactions of 7-(RCONH)-[1H]-2-oxo-1,8-naphthyridines (R = Me, Et, i-Pr, t-Bu, 1-adamantyl (1-Ad), CF₃, and C₂F₅) containing ADAD quadruple hydrogen bonding motif were studied by liquid and solid state NMR, ESI-MS, IR, and DFT calculations. ¹H NMR was used to determine the dimerization constants of i-Pr and 1-Ad congeners in CDCl₃. ¹³C and ¹⁵N cross-polarization (CP) magic angle spinning (MAS) NMR data suggest that compounds possess similar solid state structures. Further, mass spectral data reveal that in gas phase both Me and 1-Ad derivatives form also multimers due to lack of competitive solvent interactions. The structures of the gas phase multimers depend on the size of the alkyl group. These results are in agreement with quantum chemical calculations. Geometry optimization and ¹H NMR spectra show that in dimers that carry bulky alkyl groups (t-Bu and 1-Ad) certain hydrogen bonds are weaker than in Me, Et, and i-Pr derivatives while strong electron acceptors, CF₃ and C₂F₅, deshields hydrogen bonded protons but creates significant electronic F/O repulsion yielding lowering of the energy of interaction. The influence of steric effect on dimerization of quadruply hydrogen bonded dimers was correlated with the Taft E _s values.     

Synthesis and NMR Spectroscopic Characteristics of a Series of Hydrazide‐Hydrazones Containing Furoxan Ring Derived from Isoeugenoxyacetic Acid

A novel hydrazide, 2‐methoxy‐4‐(3‐methyfuroxan‐4‐yl)‐5‐nitrophenoxyacetylhydrazine, was prepared from isoeugenoxyacetic acid. The hydrazide was condensed with aromatic aldehydes to give a series of 20 hydrazide‐hydrazones incorporating the furoxan ring. The structure of obtained compounds was determined by analytical and spectral data. It was demonstrated that the two sets of resonance signals in the ¹H‐NMR and ¹³C‐NMR spectra of the examined hydrazide‐hydrazones are caused by E_N–C(O) and Z_N–C(O) conformers. The energy barriers for the conformation exchange were determined by ¹H‐NMR‐measurement at various temperatures. Among seven tested hydrazide‐hydrazones, four compounds exhibit inhibition activities in vitro on human epidermis carcinoma (KB‐cell) with IC₅₀ = 47, 68, 79, and 103 μg/mL.     

A multinuclear 1H, 13C, and 15N magnetic resonance study of ten 4-nitropyridine N-oxides

The ¹H, ¹³C, and ¹⁵N NMR chemical shifts of ten 4-nitropyridine N-oxide derivatives are assigned. The shielding of the pyridine ring nitrogen is sensitive to ring substitution through inductive effects, steric effects by ortho-substituents, and the possibility for electron delocalisation (resonance energy). In solution, 3-ethylnitrosoamino-4-nitropyridine N-oxide has two tautomers. The proposed reason is the steric crowding between vicinal 4-nitro and 3-ethylnitrosoamino groups, causing a disturbance to amino nitrogen that can delocalize its lone pair to the oxygen atom of the nitroso group.     

The protonation of ortho-methoxy- and hydroxy-benzaldehydes in FSO3H?SbF5?SO2 solution

The protonation of o-methoxy- and o-hydroxy-benzaldehydes in FSO₃H? SbF₅? SO₂ solution was investigated by ¹H NMR spectroscopy. The formation of the Z-carbonyl protonated molecule is explained by intramolecular hydrogen bonding.     

Specific features of reversible <Emphasis Type="Italic">E</Emphasis>—<Emphasis Type="Italic">Z</Emphasis>-photoisomerization of crown-containing 4-styrylpyridine complexes with various cations

The reversible photochemical E—Z-isomerization of crown-containing 4-styrylpyridine was studied. The reaction was carried out in the presence of alkaline-earth metals capable of forming complexes with the crown-ether fragment and heavy metal perchlorates (Hg²⁺, Cd²⁺) that are able to coordinate the nitrogen atom of the heterocyclic residue. The influence of complex formation on the E—Z-photoisomerization was determined by electronic spectroscopy and ¹H NMR spectroscopy. The studies performed confirm that the E—Z-photoisomerization can be controlled using supramolecular complex formation.     

Conformational analysis of N-isopropylbenzohydroxamic acids: crystal structure, DFT, and NMR studies

X-ray crystal structure determinations together with density functional theory (DFT) calculations in vacuo and NMR studies in solution have been carried out for 4-MeOC₆H₄CONPrⁱOH 2a and 3,5-(NO₂)₂C₆H₃CONPrⁱOH 2b. The results were compared with that for the respective N-methyl benzohydroxamic acids. For crystal structures as well as for DFT-optimized geometries of 2 (both isomers) in vacuo, the effect of substituents in aromatic ring manifested by changing of charges is inconspicuous. Studies of potential energy surfaces showed that libration barrier around ω ₁ = 0° is low enough to make electron conjugation feasible, and that for 2b rotation barrier around C(O)N bond is higher by 6 kcal/mol and additionally, that rotation around N–C bond is hindered. A careful analysis of low-temperature ¹H NMR spectra confirmed the greater stability of Z-2a, the greater rigidity of E-2b and the influence of solvent on both isomers population. Despite solvent-dependent conformational alteration, both 2a and 2b crystallize exclusively as E isomers from ethyl acetate solution. Correlations of absolute ¹H, ¹³C, and ¹⁵N shielding calculations with experimental data were also analyzed. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A Facile,One-Pot Synthesis of Azoic Compounds and Anthraquinone Derivatives Containing Dialkyl Phosphoryl Moieties in Multicomponent Reactions

Protonation of the reactive 1:1 intermediates produced in the reactions between triphenylphosphine and dialkyl acetylenedicarboxylates by 1-amino-anthraquinone or 1,5-diphenylcarbazone as a core dye leads to vinyl phosphonium salts, which undergo Michael addition with conjugate base of NH compounds to produce stable phosphorus ylides as novel dyes in fairly good yields. These ylides can exist in two geometrical isomers (Z) and (E) for 3, because the negative charge of the ylide moiety of these compounds are strongly conjugated with the adjacent carbonyl group. Rotation around the carbon–carbon double bond is slow in the (Z) and (E) geometrical isomers on the NMR time scale at ambient temperature. These compounds are assigned by their IR, ¹H, ¹³C NMR spectral data as well as their mass spectroscopic data.     

Study of alkaloids from the flora of the Siberian and Altai regions. 6. Crystal and molecular structure of songorine Z-oxime

Oximation of songorine afforded a mixture of its Z- and E-oximes. The crystal and molecular structure of the Z-isomer was established by X-ray diffraction analysis. Its structure was also confirmed by the spectral data (2D ¹H—¹H and ¹³C—¹H NMR spectroscopy and mass spectrometry). The structure of isomeric E-oxime was established by comparing its NMR spectroscopic data (¹H and ¹³C) with the data for the Z-isomer.     

Synthesis and Molecular Structure Characterization of Novel 1,6-Diazahexatrienes

Novel 1,6-diazahexatrienes (1a–d) are a type of aza-conjugated hexatriene containing N,N-diamino moieties. We present the oxidative dimerization of 1,1,2-trisubstituted hydrazines as a synthetic approach to 1,6-diazahexatriene derivatives, rather than the expected pyrazine and pyridazine. The proposed mechanism for formation of 1a–d involves oxidative dimerization of 1,1,2-trisubstituted hydrazines via their hydrazones. The structures of 1a–d were characterized by ¹H NMR, ¹³C NMR, and mass spectroscopy. A detailed discussion regarding the character of the three-dimensional structure of 1 is based on x-ray crystallography.     

Hydrophobic interactions in the formation of a complex between a polycationic water-soluble oxacalix[4]arene and a neutral aromatic guest

Abstract

Polycationic oxacalix[4]arene 1·4HCl was found to be able to recognise, in water, the neutral π-rich aromatic guest 2,7-dihydroxynaphthalene, despite earlier studies indicating that the binding cleft of the oxacalixarene is π rich in nature. ¹H NMR titrations at different pH values demonstrate that the tricationic receptor 1·3H⁺ displays the highest affinity towards DHN. According to a combination of NMR data and semiempirical (PM6) calculations, hydrophobic interactions play a prominent role in the formation of the complex.     

1,3‐Dipolar Cycloaddition Reactions Leading to the Synthesis of New 2,3,5‐Triaryl‐4H,2,3,3a,5,6,6a‐hexahydropyrrolo[3,4‐d]isoxazole‐4,6‐diones

Cycloaddition of C,N‐diphenylnitrones 1 to N‐aryl maleimides 2 afforded two diastereomeric isoxazolidines with high selectivity. The structure and steric configuration of the adducts have been assigned on the basis of ¹H NMR, ¹H NMR COSY, ¹³C NMR and IR spectroscopy. The π–π stacking interactions between maleimide's and nitrone's aromatic rings during the 1,3‐dipolar cycloaddition were assumed to control the exo–endo selectivity of the reaction. Thus, the exo–endo ratio depends upon the position of the substituent present on the C‐phenyl ring of the C,N‐diphenylnitrones.     

Studies of C-Glycosides. XIX. Selective Acetolysis of Primary Benzyl Ethers of C-Glucosides

Abstract

Selective acetolysis of primary benzyl ethers of O-benzyl C-glucosides has been investigated. β-anomers were shown to give fully acetylated compounds, while the α-anomers remained unchanged under the same conditions. The products were assigned by IR, ¹H NMR, ¹³C NMR, and EI-MS.     

Synthesis and structure of new β-functionalized gem-bromonitroethenes — 2-arylsulfanyl- and 2-aryloxy-3-bromo-3-nitroacrylates

Alkyl 2,3-dibromo-3-nitroacrylates react with arylthiols and phenols to give earlier unknown representatives of β-functionalized gem-bromonitroethenes, namely, 2-arylsulfanyl- and 2-aryloxy-3-bromo-3-nitroacrylates; their structure was characterized by IR, UV, and NMR (¹H, ¹³C{¹H}, HMQC, HMBC) spectroscopy. X-ray diffraction analysis showed that methyl 3-bromo-2-(4-chlorophenylsulfanyl)-3-nitroacrylate has a Z-configuration; the sulfanylbromonitrovinyl fragment in its molecule is relatively coplanar, while the ester group is almost perpendicular to the plane of the C-C double bond.

     

Synthesis and anti-inflammatory activity of N′-substituted 2-[2-(diarylmethylene)hydrazinyl]-5,5-dimethyl-4-oxohex-2-enehydrazides

New N′-substituted 2-(2-(diarylmethylene)hydrazinyl)-5,5-dimethyl-4-oxohex-2-enehydrazides were synthesized by the ring opening reaction of 3-diarylmethylenehydrazono-5-tert-butyl-3H-furan-2-ones under the action of aliphatic, aromatic, and heterocyclic acid hydrazides. The structures of the obtained compounds were confirmed by ¹H and ¹³C NMR spectroscopy, IR spectroscopy, and elemental analysis. Their anti-inflammatory activity was studied.

     

Utilization of N,N‐Dialkylcarbamic Acid Derived from Secondary Amines and Supercritical Carbon Dioxide: Stereoselective Synthesis of Z Alkenyl Carbamates with a CO2‐Soluble Ruthenium–P(OC2H5)3 Catalyst

Reversible transformation of diethylamine ( 1 ) and supercritical carbon dioxide (scCO₂) into N,N‐diethylcarbamic acid ( 2 ) was confirmed by direct acquisition of ¹H and ¹³C{¹H} NMR spectra. The equilibrium between 1 +CO₂ and 2 is strongly influenced by conditions of the supercritical state. Low temperature favors formation of carbamic acid, whereas high temperature causes decarboxylation. On the basis of the spectroscopic results of carbamic acid formation under scCO₂ conditions, the ruthenium‐catalyzed formation of alkenyl carbamates from terminal alkynes, 1 , and carbon dioxide was investigated to demonstrate the useful transformation of elusive carbamic acids. Selectivity toward the CO₂‐fixation products over enynes obtained by dimerization of the alkyne substrates was improved by the use of scCO₂ as a reaction medium. In particular, a CO₂‐soluble ruthenium complex, trans‐[RuCl₂{P(OC₂H₅)₃}₄], was found to be effective in affording Z alkenyl carbamates with high stereoselectivity.