Synthesis of p-Nitro-stilbene Derivatives with Different Linking Bonds:An Attempt to Tune Spectroscopy of Dyes with Molecular Engineering

The synthesis, characterization and spectroscopy of a range of novel substituted p‐nitro‐stilbene derivatives with different bridging bonds were presented. The molecular structure characterization was carried out with ¹H NMR, ¹³C NMR and elemental analysis. The ultraviolet/visible spectroscopy and photoluminescence of the compounds were investigated in various solvents. The maximal absorption wavelength of the nitro‐stilbene derivatives with an ether bond exhibited approximate 30 to 40 nm bathochromic shift compared to that of nitro‐stilbene dyes with an ester bond. Furthermore, the nitro‐stilbene derivatives with an ether bond displayed obvious photoluminescence, while the nitro‐stilbene derivatives with an ester bond showed weak fluorescence emission. The detection of the cyclic voltammograms of the nitro‐stilbene derivatives showed that the nitro‐stilbene compounds with different linking bonds exhibited different redox proceses at various scan rates. The theroretical calculations of HOMO and LUMO energy of nitro‐stilbene derivatives showed that the energy gaps between HOMO and LUMO of 3 and 4 were lower than those of 1 and 2 . The electron density of the frontier orbitals of nitro‐stilbene derivatives was observed to be affacted by the linking bonds, which thus made it possible to tune the spectroscopy of these dyes with chemical strategy. The differential scanning calorimetry and thermogravimetry showed that the thermal stabilities of these dyes were not much affected by the linking bond. The results presented in this paper would be great interest in development of ideal nitro‐stilbene derivatives for special purposes.     

Intramolecular hydrogen bonding in 1-nitro-5,10-dihydrophenazine derivatives

The formation of free radicals only for derivatives with a nitro group in the 1 position was observed in the oxidation of a number of 5-substituted 5,10-dihydrophenazines with lead dioxide. A long-wave absorption band was observed in the electronic spectra of the derivatives with a nitro group in the 1 position. The assumption of the formation of an intramolecular hydrogen bond in dihydrophenazines with a nitro group in the 1 position was confirmed by quantum-chemical modeling of the three structures of the 1,3-dinitro-5-phenyl-5,10-dihydrophenazine molecule. By comparison of the integral intensities of the bands of the stretching vibrations of the N-H bond in 5-substituted dihydrophenazines it was concluded that this bond is depolarized in derivatives with an intramolecular hydrogen bond.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No, 2, pp, 263–265, February, 1978.     

Bond energies and the enthalpies of formation of mono- and polyradicals in nitroalkanes 2. Nitro derivatives of ethane and propane

Based on the experimental results and the published data, the enthalpies of formation of ethane and propane nitro derivatives were obtained for both the standard state and gas phase. The bond dissociation energies of the ethane and propane nitro derivatives were calculated using the enthalpies of atomization and the energies of nonvalent interactions of nitro groups. The calculated values were compared with the kinetic data on thermal decomposition. The bond dissociation energies in radicals of the ethane and propane nitro derivatives were also calculated using the enthalpies of atomization and the energies of nonvalent interactions of nitro groups. Regularities of changes in the bond dissociation energies of the ethane and propane nitro derivatives and their radicals were established.     

Mesomeric dipole moments. Part 12

The dipole moments of para-substituted azoxybenzenes (1, a-e) and phenylazoxycyanides (2, a-e) were analyzed in terms of bond moments and additional contributions expressing electron delocalization. The results are compatible with a significant participation of the polar mesomeric formula B (25% or 34% for1 and2, respectively), the N-O bond acquiring considerable double-bond character. Comparison of known x-ray structures reveals that this bond is significantly shortened, whereas the N=N bond is extended only very slightly. Hence we can consider the possibility that the N1 atom allocates somewhat more than eight valence electrons, similarly to nitro compounds. In all respects the properties of the azoxy group are between those of the nitro and imino-N-oxide groups.Part 11 appears in Exner, O.J. Phys. Org. Chem. 1990,3, 190.     

Indole derivatives.

The nature of the products of reduction of nitro compounds of the indole series containing a polysulfide chain depends on the length of the latter. In mono- and disulfides only the nitro groups are reduced, and diamino monosulfides and diamino disulfides are formed. In the reduction of the dinitro trisulfide the chain is cleaved and an amino thiol is formed. The reduction of acetylthionitro compounds is accompanied by migration of the S-N bond, as a result of which an acetamido thiol is formed.     

A spectrophotometric and polarographic investigation of three new cyclohexene-substituted benzodiazepines

Three recently introduced benzodiazepine derivatives, tetrazepam (I), nortetrazepam (II) and menitrazepam (III) have been subjected to spectral and polarographic investigation. From the ultraviolet spectral data their pK(a)-values have been determined: 4.28 (I), 4.3 (II) and 3.5 (III). From the polarographic measurements it can be concluded that in I and II the 4,5 CN double bond is reduced with 2 electrons. For the first time for the benzodiazepine series it has been observed that in slightly alkaline solutions this process takes place in two separate 1-electron steps. In III, first the aromatic nitro group is reduced to a hydroxylamine group, then at more negative potentials the CN double bond is also reduced; its reduction wave mostly coalesces with that for the 6-electron reduction of the nitro group to an amino group. A differential pulse polarographic method is presented, for the determination of I, II, III at concentrations as low as 10(-7)M.     

Bond energies and formation enthalpies of mono- and polyradicals in nitroalkanes 1. Nitromethanes

The enthalpies of formation of nitromethane derivatives were obtained on the basis of experimental and literature data. The procedure for the calculation of the bond dissociation energies in nitromethanes from the atomization enthalpies and energies of nonvalent interactions of nitro groups was proposed. The calculated values were compared with the data on the thermal decomposition kinetics. The atomization enthalpies and energies of nonvalent interactions of nitro groups were also used for the calculation of the bond dissociation energies in radicals.     

The photochemistry of flutamide and its inclusion complex with beta-cyclodextrin. Dramatic effect of the microenvironment on the nature and on the efficiency of the photodegradation pathways

The photochemistry of the anticancer drug flutamide (FM), 2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]propanamide, in homogeneous media and in the beta-cyclodextrin (beta-CD) cavity has been investigated. The photoreactivity of the free molecule has been rationalized on the basis of an intramolecular nitro to nitrite rearrangement followed by cleavage of the nitrite intermediate. The twisted geometry of the nitro group with respect to the aromatic plane plays a key role in triggering such a photoprocess. Incorporation of FM in the beta-CD cavity leads to dramatic effects on both the efficiency and the nature of the photochemical deactivation pathways of the guest molecule. A 20-fold increase in the FM photodecomposition quantum yield and the formation of photoproducts originated by both reduction of the nitro group and cleavage of the amide bond were observed in the presence of the macrocycle. Such a behavior cannot be attributed exclusively to the micropolarity of beta-CD and/or to its role as a reactant. The induced circular dichroism spectra and the nature of the photoproducts formed in these experimental conditions provide indications that the photoreactivity in the beta-CD microenvironment could likely be mediated by structural changes of FM upon complexation.     

Solvatochromism of Heteroaromatic Compounds: XX. 4(5)-Nitroimidazole

4(5)-Nitroimidazole in solution is stabilized as the 5-nitro isomer due to formation of hydrogen bond with an aprotic protophilic solvent. Amphiprotic medium favors displacement of the tautomeric equilibrium toward the 4-nitro isomer via formation of a solvate complex where 4-nitroimidazole acts as hydrogen bond acceptor. The observed specific solvatochromic effect in the UV spectrum of 4-nitroimidazole and related heterocyclic nitro compounds is determined by the electronic configuration of the excited ,^*-state.     

Investigation of correlation between impact sensitivities and nitro group charges in nitro compounds

A new method of calculating the Mulliken net charges of the nitro group, Q(NO)()2, to assess impact sensitivities for nitro compounds is established. All calculations including optimizations and Mulliken population and frequency analyses are performed by density functional theory (DFT) and the general gradient approximation (GGA) method in Acceryls' code Dmol(3) with the Beck-LYP hybrid functional and the DNP basis set. As a result, the charges on nitro group can be regarded as a structural parameter to estimate the impact sensitivity on the bond strength, oxygen balance, and molecular electrostatic potential. The compound with more -Q(NO)()2 will be insensitive and gives a large value of impact sensitivity H(50)(). This method considering the molecular structure is applicable for almost all nitro compounds when the C-NO(2), N-NO(2), or O-NO(2) bond is the weakest in the molecule. According to the results in this paper, the compounds with -Q(NO)()2 >0.23e show H(50)() 相似文献   

Novel ring-cleaving reaction of 4-nitro-1,1,2,2,9,9,10,10-octafluoro[2.2]paracyclophane with nucleophiles

When 4-nitro-AF4 is treated with nucleophiles such as alkoxides and cyanide, a novel ring opening, cyclophane destroying reaction is observed whereby, via an S_NAr mechanism, the nucleophile attacks the bridgehead aryl carbon vicinal to the nitro group with subsequent aryl-CF₂ bond cleavage.     

Azole. 45.

The three title compounds, namely (Z)‐1‐(4,5‐di­nitro­imidazol‐1‐yl)‐3‐morpholinopropan‐2‐one 2,4‐di­nitro­phenyl­hydrazone, C₁₆H₁₇N₉O₉, (IV), (Z)‐3‐morpholino‐1‐(4‐morpholino‐5‐nitro­imidazol‐1‐yl)propan‐2‐one 2,4‐di­nitro­phenyl­hydrazone, C₂₀H₂₅N₉O₈, (Va), and (E)‐3‐morpholino‐1‐(4‐morpholino‐5‐nitro­imidazol‐1‐yl)propan‐2‐one 2,4‐di­nitro­phenylhydra­zone tetra­hydro­furan solvate, C₂₀H₂₅N₉O₈·C₄H₈O, (Vb), have been prepared and their structures determined. In (IV), the C‐4 nitro group is nearly perpendicular to the imidazole ring and the C‐4—NO₂ bond length is comparable to the value for a normal single Csp²—NO₂ bond. In (IV), (Va) and (Vb), the C‐­5 nitro group deviates insignificantly from the imidazole plane and the C‐5—NO₂ bond length is far shorter in all three compounds than C‐4—NO₂ in (IV). In consequence, the C‐4 nitro group in (IV) is easily replaced by morpholine, while the C‐5 nitro group in (IV), (Va) and (Vb) shows an extraordinary stability on treatment with the amine. The E configuration in (Vb) is stabilized by a three‐centre hydrogen bond.     

Trigger bond analysis of nitroaromatic energetic materials using wiberg bond indices

The identification of trigger bonds, bonds that break to initiate explosive decomposition, using computational methods could help direct the development of novel, “green” and efficient high energy density materials (HEDMs). Comparing bond densities in energetic materials to reference molecules using Wiberg bond indices (WBIs) provides a relative scale for bond activation (%ΔWBIs) to assign trigger bonds in a set of 63 nitroaromatic conventional energetic molecules. Intramolecular hydrogen bonding interactions enhance contributions of resonance structures that strengthen, or deactivate, the C NO₂ trigger bonds and reduce the sensitivity of nitroaniline‐based HEDMs. In contrast, unidirectional hydrogen bonding in nitrophenols strengthens the bond to the hydrogen bond acceptor, but the phenol lone pairs repel and activate an adjacent nitro group. Steric effects, electron withdrawing groups and greater nitro dihedral angles also activate the C NO₂ trigger bonds. %ΔWBIs indicate that nitro groups within an energetic molecule are not all necessarily equally activated to contribute to initiation. %ΔWBIs generally correlate well with impact sensitivity, especially for HEDMs with intramolecular hydrogen bonding, and are a better measure of trigger bond strength than bond dissociation energies (BDEs). However, the method is less effective for HEDMs with significant secondary effects in the solid state. Assignment of trigger bonds using %ΔWBIs could contribute to understanding the effect of intramolecular interactions on energetic properties. © 2018 Wiley Periodicals, Inc.     

Investigation of intramolecular sulfur-nitro interactions in 2-(2′-pyridylthio)-3-nitropyridine by 13C-NMR spectroscopy and x-ray crystallography

The single crystal X-ray diffraction structure of 2-(2′-pyridylthio)-3-nitropyridine is reported. A non-bonded interaction was observed between the sulfur atom and one of the oxygen atoms of the nitro group with an interatomic distance of 2.678 A. Examination of the molecule's behavior in solution by ¹³C-nmr spin-lattice (T₁) relaxation measurements showed the non-nitro bearing pyridyl ring to reorient anisotropically about the C2′-C5′ bond axis. In contrast, the nitro substituted pyridine ring did not appear to exhibit anisotropic reorientation about the corresponding C2-C5 bond axis. Rather, approximately equivalent relaxation times were noted for all protonated ring carbons, indicating that the relaxations of this portion of the molecule were governed by the overall isotropic reorientation of the system. Based on these observations, it was concluded that the intramolecular sulfur-nitro interaction also operates in the solution state and is sufficiently strong to prevent free rotation of the substituted portion of the molecule about the C2-S bond axis.     

Theoretical studies on polynitrobicyclo[1.1.1]pentanes in search of novel high energy density materials

Bicyclo[1.1.1]pentane is a highly strained hydrocarbon system due to close proximity of nonbonded bridge head carbons. Based on fully optimized molecular geometries at the density functional theory using the B3LYP/6-31G* level, densities, detonation velocities, and pressures for a series of polynitrobicyclo[1.1.1]pentanes, as well as their thermal stabilities were investigated in search for high energy density materials (HEDMs). The designed compounds with more than two nitro groups are characterized by high heat of formation and magnitude correlative with the number and space distance of nitro groups. Density was calculated using the crystal packing calculations and an increase in the number of nitro groups increases the density. The increase in density shows a linear increase in the detonation characteristics. Bond dissociation energy was analyzed to determine thermal stability. Calculations of the bond length and bond dissociation energies of the C-NO₂ bond indicate that this may be the possible trigger bond in the pyrolysis mechanism. 1,2,3-Trinitrobicyclo[1.1.1]pentane (S3), 1,2,3,4-tetranitrobicyclo[1.1.1]pentane (S4), and 1,2,3,4,5-pentanitrobicyclo[1.1.1]pentane (S5) have better energetic characteristics with better stability and insensitivity, and as such may be explored in defense applications as promising candidates of the HEDMs series.     

Computational study on energetic properties of nitro derivatives of furan substituted azoles

Density functional theory has been used to investigate geometries, heats of formation (HOFs), C-NO₂ bond dissociation energies (BDEs), and relative energetic properties of nitro derivatives of azole substituted furan. HOFs for a series of molecules were calculated by using density functional theory (DFT) and Møller–Plesset (MP2) methods. The density is predicted using crystal packing calculations; all the designed compounds show density above 1.71 g/cm³. The calculated detonation velocities and detonation pressures indicate that the nitro group is very helpful for enhancing the detonation performance for the designed compounds. Thermal stabilities have been evaluated from the bond dissociation energies. Charge on the nitro group was used to assess the impact sensitivity in this study. According to the results of the calculations, tri- and tetra-nitro substituted derivatives reveal high performance with better thermal stability.     

Denitrohydrogenation of aliphatic nitro compounds and a new use of aliphatic nitro compounds as radical precursors

Aliphatic nitro groups are replaced by hydrogen on treatment with tributyltin hydride which proceeds via free radical chain processes. As the nitro group is selectively denitrated and other reducible groups are not affected with tributyltin hydride, this reaction can be used as a method for removing the nitro group from polyfunctional compounds. The radical intermediates generated via denitration can be also used for the carbon-carbon bond forming reactions.     

Mass spectral rearrangements in benzylidene hippuric esters

The mass spectra of a series of hippuric esters have been determined. A variety of novel rearrangements induced by the presence of a formed benzyl carbonium ion has been rationalized with the aid of high resolution measurements and isotopic and substituent labeling. An eight centered rearrangement is proposed for the observed transfer of oxygen from a nitro group to a double bond.     

Reactions of Substituted Boryl Radicals with Nitroalkanes. EPR, Kinetic, and Product Studies

The radical-initiated reaction of amine-boranes and phosphine-boranes, LBH(3) (L = R(3)N, R(3)P) with aliphatic nitro compounds has been investigated in order to explore the possibility of reducing tertiary nitroalkanes to the corresponding hydrocarbons. In all the examined cases boroxy nitroxides, RN(O(*))OBLH(2), resulting from the addition of ligated boryl radicals, LBH(2)(*), to an oxygen atom of the nitro group were detected and characterized by EPR spectroscopy. This reaction occurs at room temperature with a rate constant of 1.5 x 10(7) M(-)(1) s(-)(1) for LBH(2)(*) = Me(3)NBH(2)(*) and RNO(2) = Me(3)CNO(2). The boroxy nitroxides from tertiary nitroalkanes decay by a fragmentation reaction occurring with cleavage of the nitrogen-oxygen bond, rather than of the carbon-nitrogen bond as would be required for the reduction to the corresponding alkane to take place. The Arrhenius parameters for this fragmentation have been determined in few cases.     

Ab initio and density functional studies on bonding nature of the N?N bonds in 1,2,5‐trinitroimidazole and 1,2,4,5‐tetranitroimidazole

The bonding nature of the N N bonds in 1,2,5‐trinitroimidazole ( I ) and 1,2,4,5‐tetranitroimidazole ( II ) was examined with various levels of ab initio and density functional (DF) theories. The second‐order Møller–Plesset perturbation method (MP2) with the 6‐31G** basis set has predicted significantly long N N bond lengths in I and II , that is, 1.737 and 1.824 Å, respectively. Two DF theories, BLYP/6‐31G** and BP86/6‐31G**, provided similar results to those of MP2/6‐31G**. On the other hand, Hartree–Fock (HF) calculation with the 6‐311++G** basis set evaluated these bond lengths of I and II to be 1.443 and 1.414 Å, respectively. Bond properties including the bond critical density are strongly dependent on the equilibrium bond length. Thus, accurate prediction of geometric parameters is of particular importance to derive reliable bond properties. Especially, a substantial difference in bonding properties is observed when the electron correlation effect is included. According to our analyses with bonding natures and CHELPG charges at the MP2 level, (1) the N N bonds of I and II appear to have a significant ionic nature, and (2) the 1‐nitro group bears a considerable positive charge and has attractive electrostatic interactions with O atoms of adjacent nitro groups. Although all the theories utilized in this study predict that both I and II are stable in their potential‐energy surfaces, significantly long N N bond lengths calculated with MP2 and DF theories imply a strong hyperconjugation effect, which may explain a tendency to form a salt in these compounds easily. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 72: 145–154, 1999