Physicochemical studies of the structure of N,N′-dinitrourea and its salts

The properties and behavior of dinitrourea and its potassium and dipotassium salts in different solvents have been studied by IR and UV spectroscopy. In different media, dinitrourea can exist in several tautomeric forms. An XRD study of the potassium and dipotassium salts of dinitrourea revealed a tendency toward equalization of the bond lengths of the C-N⁻-NO₂ fragments compared with those of C-NH-NO₂, which agrees with the results of quantum-chemical calculations.     

Franck-Condon simulation of the photoelectron spectrum of AsCl₂ and the photodetachment spectrum of AsCl ₂⁻ employing UCCSD(T)-F12a potential energy functions: IE and EA of AsCl₂

The currently most reliable theoretical estimates of the adiabatic ionization energies (AIE₀) from the X?²B₁ state of AsCl₂ to the X?¹A₁ and ã³B₁ states of AsCl, and the electron affinity (EA₀) of AsCl₂, including ΔZPE corrections, are calculated as 8.687(11), 11.320(23), and 1.845(12) eV, respectively (estimated uncertainties based on basis‐set effects at the RCCSD(T) level). State‐of‐the‐art ab initio calculations, which include RCCSD(T), CASSCF/MRCI, and explicitly correlated RHF/UCCSD(T)‐F12x (x = a or b) calculations with basis sets of up to quintuple‐zeta quality, have been carried out on the X?²B₁ state of AsCl₂, the X?¹A₁, ã³B₁, and ùB₁ states of AsCl, and the X?¹A₁ state of AsCl. Relativistic, core correlation and complete basis‐set (CBS) effects have been considered. In addition, computed UCCSD(T)‐F12a potential energy functions of relevant electronic states of AsCl₂, AsCl, and AsCl were used to calculate Franck–Condon factors, which were then used to simulate the valence photoelectron spectrum of AsCl₂ and the photodetachment spectrum of AsCl, both yet to be recorded. Lastly, we have also computed the AIE and EA values for NCl₂, PCl₂, and AsCl₂ at the G4 level and for SbCl₂ at the RCCSD(T)/CBS level. The trends in the AIE and EA values of the group V pnictogen dichlorides, PnCl₂, where Pn = N, P, As, and Sb, were examined. The AIE and EA of PCl₂ were found to be smaller than those of AsCl₂, contrary to the order expected from the IE values of P and As. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011     

FT-IR study of the conformation and proton acceptor ability of N-tertiobutoxycarbonylsarcosine N′-methylamide and N-tertiobutoxycarbonylsarcosine N′,N′-dimethylacetamide

Two model dipeptides, N-tertiobutoxycarbonylsarcosine N′-methylamide (BSMA) and N-tertiobutoxycarbonylsarcosine N′,N′-dimethylamide (BSDA) are investigated by FT-IR spectrometry. The conformation of BSMA is very sensitive to the environment. In solvents of weak polarity (carbon tetrachloride, cyclohexane), BSMA accomodates the extended and seven-membered ring conformation, but in 1,2-dichloroethane, the C₇ conformers are greatly destabilized. Hydrogen bonding between BSMA or BSDA and phenols is studied in carbon tetrachloride. The thermodynamic data (equilibrium constants and enthalpies of complex formation) show that the BSMA complexes are stronger than the BSDA complexes. The spectroscopic data suggest that for BSMA, complex formation occurs at the O atom of the amide function while for BSDA about 50% of the complexes are formed on the O atom of the urethane group. The differences between the two sarcosine dipeptides are discussed in terms of cooperative and steric effects. It can be concluded that the global polarity of the medium exerts a greater influence on the conformation of the C₇ dipeptides than the specific interactions taking place on a given site of the molecule.     

Elucidating the N−N and C−N Bond-breaking Mechanism in the Photoinduced Formation of Nitrile Imine

In this study, we revealed the significance of chemical bonding for the photochemically induced mechanism of 2-phenyl tetrazole derivatives generating nitrile imines. The correlated electron localization function shows that the formation of imine nitrile involves two key bond events: (i) the heterolytic C−N breakage taking place in the T₁ state and (ii) the homolytic N−N rupture occurring in the T₂ excited state. In particular, a cation-radical specie results from the C−N cleavage, whereas the N−N rupture creates a biradical resonant form of imine nitrile. Additionally, we noticed that the substantial pair delocalization of the C−C-N bonded structure could play a significant role in the conversion of the biradical imine nitrile into both the propargylic and allenic forms via the T₁→S₀ deactivation.     

The structure effect of N,N,N′,N′-alkylamide in the extraction of uranium and thorium

In this paper, nine N,N,N,N-tetraalkyldiamides have been synthesized and the extracting ability for uranium and thorium under different conditions has been studied. All results were compared with those obtained by using tributyl phosphate (TBP) under exactly the same conditions. The extracting ability of thorium and uranium for different N,N,N,N-tetraalkyldiamides is discussed.     

Calorimetric study of the reaction between formic acid and N,N,N′,N′-tetramethylethylenediamine from the aspect of thermal energy storage

The attack by formic acid on the nitrogen electron pairs of N,N,N,N-tetramethylethylenediamine leads to the stoichiometric salt or to many other complexes with different molar fractions. Physical and thermodynamic parameters of two adducts, obtained by calorimetric study, are discussed in terms of their use as potential phase change materials in thermal energy storage because of their large heat of fusion between 288 and 333 K.

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Zusammenfassung Bei der Einwirkung von Ameisensäure auf die Elektronenpaare von N,N,N,N-Tetramethylethylendiamin entsteht ein stöchiometrisches Salz oder mehrere andere Komplexe mit unterschiedlichem Molenbruch. Es werden physikalische und thermodynamische Parameter zweier bei der kalorimetrischen Untersuchung erhaltenen Addukte hinsichtlich ihrer Verwendung als potentielle Phasenwechselsubstanzen bei der thermischen Energiespeicherung diskutiert, da sie im Bereich 288–333 K eine große Schmelz-wärme besitzen.

     

Diastereomeric Difference of the Self-Inclusion Complex of N(N′-Formyl-Phenylalanyl)-Deoxyamino-β-Cyclodextrin Caused by the Interaction between the Arm and the Rim of the Cavity

A complete assignment of proton resonances for N(N-formyl d-phenylalanyl)-deoxyamino--cyclodextrin (1d) was performed by means of 1D and 2D NMR,¹H–^1H-COSY, ¹H–^13C-COSY, TOCSYand NOESY spectroscopy. Based on 2D-NMR ROESY and circular dichroism spectroscopy, the conformation of 1d was determined; the phenyl group stays inside the distorted cyclodextrin (CyD) cavity forming a self-inclusion complex, which is almost the same as N(N-formyl l-phenylalanyl)-deoxyamino--CyD (1l). The remarkable diastereomeric difference was observed in the chemical shifts of H(5) and H(6) protons at the narrow rim of the CyD cavity and induced circular dichroism spectra. These results suggest the existence of hydrogen bonds between the hydroxyl group on CyD and the amide groups on the arms, which provides the difference in the molecular recognition properties.     

2,7-Dibromonaphthalene and 4,4′-dibromobiphenyl in the synthesis of oxadiamine N,N, N′, N′-tetraaryl derivatives and studies of formation of bismacrocyclic compounds from them

Russian Chemical Bulletin - The Pd-catalyzed tetraarylation of diamines and oxadiamines with 2,7-dibromonaphthalenes and 4,4′-dibromobiphenyl was studied. These reactions gave the...     

Calorimetric study of the solubilization of ethylenediamine,N,N-dimethylaminoethylamine and N,N,N′,N′-tetramethylethylenediamine by reversed AOT micelles

Distribution constants and standard enthalpies of transfer of ethylenediamine (en), N,N-dimethylaminoethylamine (dmen) and N,N,N,N-tetramethylethylenediamine (tmen) partitioned between n-heptane and water containing reversed sodium bis(2-ethylhexyl) sulfosuccinate (AOT) micelles as a function of the molar concentration ratio R (R=[water]/[AOT]) were evaluated by a calorimetric method. The results show that en, dmen and tmen molecules, solubilized in the reversed micelles, are distributed between the micellar aqueous core and the micellar palisade layer. An analysis of the thermodynamic parameters of the partition process demonstrates the peculiar solvent properties of the water containing reversed AOT micelles.     

Synthesis of N‐Benzylated Anilines from the Reaction of Anilines and Benzyl Chloroformate

Abstract

Reactions of benzyl chloroformate with a series of substituted anilines produced N‐carbobenzyloxy “CBZ” products along with the unexpected N‐benzylated “Bn” compounds. Reaction of aniline, 1a, gave the CBZ, or 2a, and Bn, or 3a, products in 29% and 14% yield, respectively. For 2‐nitro‐, 2‐bromo‐, and 2‐bromo‐5‐nitroanilines, the N‐benzylated compounds were produced exclusively. However, 2‐methoxy‐, 4‐bromo, 4‐iodo, and 4‐ethylanilines gave mainly CBZ products. Other compounds reported in this study gave mixtures of the two products. For 4‐chloro‐3‐nitroaniline, in addition to the Bn and CBZ products (53% and 14% yield, respectively), a N,N‐dibenzylated product was isolated in 27% yield. Collectively, the results indicated that electron‐withdrawing groups, particularly at the ortho position, directed the formation of Bn compounds, whilst electron‐donating groups, especially at the ortho and para positions, favored the synthesis of CBZ products.     

Use of novel cardanol-porphyrin hybrids and their TiO₂-based composites for the photodegradation of 4-nitrophenol in water

Cardanol, a well known hazardous byproduct of the cashew industry, has been used as starting material for the synthesis of useful differently substituted "cardanol-based" porphyrins and their zinc(II), copper(II), cobalt(II) and Fe(III) complexes. Novel composites prepared by impregnation of polycrystalline TiO? powder with an opportune amount of "cardanol-based" porphyrins, which act as sensitizers for the improvement of the photo-catalytic activity of the bare TiO?, have been used in the photodegradation in water of 4-nitrophenol (4-NP), which is a toxic and bio-refractory pollutant, dangerous for ecosystems and human health.     

Crystal Structure of the Addition Compound of N,N′-Bi(2-pyridylmethyl)-Oxamide and the Complex of Copper with 1,10-Phenanthroline

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Stopped-flow spectrophotometric study of the kinetics and mechanism of CO₂ uptake by cis-[Cr(C₂O₄)(BaraNH₂)(OH₂)₂]+ cation and the acid-catalyzed decomposition of cis-[Cr(C₂O₄)(BaraNH₂)OCO₂]- anion in aqueous solution

The kinetics of CO(2) uptake by the cis-[Cr(C(2)O(4))(BaraNH(2))(OH(2))(2)]+ complex cation and the acid hydrolysis of the cis-[Cr(C(2)O(4))(BaraNH(2))OCO(2)]- complex anion (where BaraNH(2) denotes methyl 3-amino-2,3-dideoxy-b-D-arabino-hexopyranoside) were studied using the stopped-flow technique. The reactions under study were investigated in aqueous solution in the 288-308 K temperature range. In the case of the reaction between CO(2) and cis-[Cr(C(2)O(4))(BaraNH(2))(OH(2))(2)]+ cation variable pH values (6.82-8.91) and the constant ionic strength of solution (H+, Na+, ClO(4)- = 1.0) were used. Carbon dioxide was generated by the reaction between sodium pyruvate and hydrogen peroxide. The acid hydrolysis of cis-[Cr(C(2)O(4))(BaraNH(2))OCO(2)]- was investigated for varying concentrations of H+ ions (0.01-2.7 M). The obtained results enabled the determination of the number of steps of the studied reactions. Based on the kinetic equations, rate constants were determined for each step. Finally, mechanisms for both reactions were proposed and discussed. Based on the obtained results it was concluded that the carboxylation (CO(2) uptake) reactions of cis-[Cr(C(2)O(4))(BaraNH(2))(OH(2))(2)]+ and the decarboxylation (acid hydrolysis) of the cis-[Cr(C(2)O(4))(BaraNH(2))OCO(2)]- are the opposite of each other.     

Synthesis of Fully Protected N‐Arylglycosylamines and Factors Affecting the Configuration of C1‐Substituents of N‐Arylglycosylamines

Abstract

An efficient method was reported for preparation of N‐arylglycosylamines in aqueous THF under reflux in good yields. The factors affecting the configuration of C₁‐substituents of N‐aryglycosylamines was investigated, that is, the influence of solvents, substituents of aromatic amines, and protecting groups of monosaccharides on the ratio of α‐ and β‐N‐arylglycosylamines.     

Influence of π-stacking on the N7 and O6 proton affinity of guanine

The influence of π-stacking interactions between guanine (G) and the side chain of tyrosine (Tyr) on the N7 and O6 proton affinities of guanine and on the capability of these sites to act as hydrogen bond acceptors is analyzed at the B3LYP-D, M05-2X and MP2 levels of theory. With all methods, results from full geometry optimizations indicate that stacking interactions increase the N7 and O6 proton affinities by about 5–6 kcal mol^?1, the increase being slightly larger for N7. Consistently with these results, hydrogen bond distances between guanine and one water molecule decrease in the stacked system. Moreover, interaction energy between H₂O and (G-Tyr) is found to be 2–3 kcal mol^?1 larger than in G···H₂O. This strengthening arises from the additional Tyr–H₂O stabilizing interactions and from a cooperative interplay between stacking and hydrogen bond forces.     

Experimental and theoretical study of the dissociation enthalpy of the N–O bond on 2-hydroxypyridine N-oxide: theoretical analysis of the energetics of the N–O bond for hydroxypyrydine N-oxide isomers

The standard (p^∘=0.1 MPa) molar enthalpy of formation of crystalline 2-hydroxypyridine N-oxide was measured, at T=298.15 K, by static bomb calorimetry and the standard molar enthalpy of sublimation, at T=298.15 K, was obtained using Calvet microcalorimetry. These values were used to derive the standard molar enthalpy of formation of 2-hydroxypyridine N-oxide in gaseous phase, and to evaluate the dissociation enthalpy of the N–O bond. Additionally, high-level density functional theory calculations using the B3LYP hybrid exchange-correlation energy functional have been performed for the three isomers of hydroxypyridine N-oxide in order to confirm the experimental trend for the dissociation enthalpy of the (N–O) bond.     

Structures and stability of N9, N9 − and N9 + clusters

 Ab initio molecular orbital calculations for N₉, N⁻ ₉ and N⁺ ₉ isomers were carried out at the HF/ 6-31G*, B3PW91/6-31G*, B3LYP/6-31G* and MP2/ 6-31G* levels of theory. Stable equilibrium geometric structures were determined by harmonic vibrational frequency analyses at the HF/6-31G*, B3PW91/6-31G* and B3LYP/6-31G* levels of theory. The most stable free-radical N₉ cluster is structure 1 with C _{2 v} symmetry and that of anion N⁻ ₉ is structure 3 with C _s symmetry. Only one stable structure of the N⁺ ₉ cation with C _{2 v} symmetry was predicted. Their potential application as high-energy-density materials has been examined. Received: 15 June 1999 / Accepted: 11 October 1999 / Published online: 14 March 2000     

Study on the influence of ageing on chemical and mechanical properties of N,N′-dimethyl-N,N′-diphenylcarbamide stabilized propellants

Double-base propellants undergo chemical, physical and mechanical changes upon ageing, leading to changes in ballistic performance and presenting explosive hazards. This report studies the variation of chemical and mechanical properties of aged N,N′-dimethyl-N,N′-diphenylcarbamide (methyl centralite) stabilized propellants in order to simulate and evaluate the natural ageing throughout the artificial one. Therefore, a comparative study of stabilizer depletion, plasticizers content, heat of combustion and mechanical properties such as storage modulus, loss modulus and damping of naturally and artificially aged propellants has been carried out by the following techniques: high-performance liquid chromatography (HPLC), thermogravimetric analyzer (TG), calorimeter of combustion and dynamic mechanical analyzer (DMA), respectively. The results obtained show that all properties are closely connected. In addition, the determination of stabilizer depletion, plasticizers evaporation, decrease of heat of combustion and mechanical properties are very useful for a better understanding of the decomposition and ageing behaviour of propellants. The HPLC investigation of stabilizer has shown good stability of the propellants. The results obtained for DMA have shown that some considerable changes of the mechanical and viscoelastic properties of the propellants occurred during ageing. These results confirm the results obtained by TG for the reduction of the nitroglycerine amount and the decrease of the heat of combustion.     

Studies of the dissociation and the protonation of TB-chlorosulphophenol

The dissociation constant of each step for TB-chlorosulphophenol has been determined by potentiometric method, and the thermodynamic constants, △G°, △H° and △S°, of the dissociation process have been calculated. The protonation constants were measured by the spectrophotometric method. The pH values of various forms of anions of the chromogenic reagent at their concentrations were also calculated.