Electronic spectra of organic molecules and their interpretation—IV Effect of terminal atoms with lone electron pairs on the K-bands of conjugated systems

The effect of the hydroxyl, methoxyl, mercapto, methylmercapto, and amino groups as well as of the charged O⁻ and S⁻ atoms (X) at the ends of the conjugated systems (1) and (2) on the position of the corresponding K-bands is discussed.

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The conclusions of earlier investigations are confirmed. The “effective” electron migration in one direction along the absorbing conjugated system (indicated by the long arrow) determines almost exclusively the stability of the observed excited state. The displacement of a K-band to longer wavelengths on introduction of a terminal group (X) can be due either to an electron shift in the substituted system coinciding with the direction of the effective electron migration of the transition or to an increased electron polarisability of the terminal group itself.

A consistent qualitative, but very detailed, theoretical interpretation of these observations is possible by a consideration of the electronic perturbations in the excited state due to Heisenberg resonance, if the molecules are accepted as being built up of localised bonds and involving inductive (inductomeric) electron shifts only.     

Ligand migrations during the formation of some palladium-rhodium heterodinuclear complexes

A new Pd(I)-Rh(II) heterodinuclear complex, trans-(NC)₂---(CH₃0)₃PRh(μ-dppm)₂PdC1 (2a), was prepared by treatment of [(cod)RhCI]₂ with (CH₃0)₃P and trans-(NC)₂Pd(dppm)₂ (1) (dppm = bis(diphenylphosphino)methane, COD = 1,5-cyclooctadiene) and characterized by ³¹P NMR spectroscopy and single-crystal X-ray structure determination. The single crystal of complex 2a is triclinic; its space group

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, = 94.43(3), β = 106.55(3), γ = 87.86(3)°. The Rh---Pd bond distance is 2.7835(5) Å. The molecular structure of this complex suggests that its formation reaction includes: (i) ligand migrations of the Cl⁻ from the Rh center to the Pd center and the two CN⁻ groups from the Pd center to Rh center; (ii) the intermetallic one-electron transfer indicated by the alteration from Rh(I) and Pd(II) to Rh(1I) and Pd(I) respectively; (iii) the Pd(I)---Rh(II) bond formation by pairing one electron from Rh(II) with one electron from Pd(I). The differences of chemical shifts of the phosphorus atoms coordinated to the Pd center in the Pd---Ag complexes and the Pd---Rh complexes are discussed.     

Micellisation of β-casein

We measured the dynamic (DLS) and static (SLS) light scattering behaviour of β-casein solutions in a 25 mM Na phosphate buffer at neutral pH as a function of temperature. At low temperatures (0 °C) β-casein is predominantly in a monomer state. With rising temperature micelles are formed with a (concentration-dependent) transition temperature in the range 15–30 °C. The transition is accompanied by a clear positive excess heat capacity. In DLS we observe two relaxation modes. The fast mode is attributed to the diffusive motion of the micelles and leads to a hydrodynamic radius of about 12 nm. The slow mode cannot be attributed to ‘physical’ particles. It is attributed to polydispersity or equivalently to long-range concentration fluctuations as proposed by Leclerc and Calmettes [15 and 16]. From SLS measurements we obtained the molecular mass and divided by the mass of a monomer (24 kDa) it gives the micellisation number, which seems to level off to about 30 at 40 °C. The measured micellisation number is predicted quite satisfactorily from a thermodynamic model for the calorimetric data as developed by Mikheeva et al. [26] and based on the shell model of Kegeles [24 and 25].     

Dipole polarizability pseudospectra and C6 dispersion coefficients for H2–H2

Pseudostate decomposition of static dipole polarizabilities for ground state H₂⁺ from a Givens-Householder diagonalization of the excitation operator (

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H" height="17" width="20">₀−E₀) over an N-term basis of appropriate symmetry allows for a rapidly convergent evaluation of C₆ dispersion coefficients for H₂⁺–H₂⁺. 27-term pseudospectra of hypergeneralized James functions with a 30-term GGJ⁺ unperturbed wavefunction with an optimized scale factor δ=0.918 at R=2₀ give C₆ and γ₆ values that are accurate to no less than nine significant figures.     

Electron solvation in methanol revisited

Suggestions for the mechanism of electron solvation in methanol during the last three decades were mostly based on limited time resolution measurements, or indirect observations. The two-channel solvation scheme proposed by Lewis and Jonah (1986) based on indirect observations in electron scavenging experiments is checked here to see if it is in accordance with recent sub-picosecond pump-and-probe laser experimental results. We confirm the applicability of this solvation mechanism and calculate quantitative kinetic and spectral parameters involved.     

Use of the velocity of sound in predicting the PVT relations

Thermodynamic properties of fluids are generally calculated from the PVT relations through equations of state. The majority of existing equations of state require the critical properties or intermolecular potential energy parameters as their input data. In many cases, such properties are neither available nor they can be accurately estimated.

One accessible and accurately measurable property of substances is the velocity of sound. In this report a method is introduced through which one can predict the PVT behavior of fluids using the velocity of sound data. A general mathematical relationship,

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expressing the velocity of sound, c, in terms of the hard-core velocity of sound, c_hs, and thermodynamic properties is derived. One may use this equation to extract PVT data from cVT data, or vice versa. As an example the virial coefficients, the Lennard-Jones intermolecular potential parameters, and the constants of the van der Waals equation of state for a number of pure fluids are calculated using the velocity of sound data. Utility of this method is particularly attractive for such compounds as heavy hydrocarbons, unstable fluids, and newly designed molecules for which intermolecular parameters and critical properties are not available.     

Predictive models to describe VLE in ternary mixtures water + ethanol + congener for wine distillation

The modeling of liquid–vapor equilibrium in ternary mixtures that include substances found in alcoholic distillation processes of wine and musts is analyzed. In particular, vapor–liquid equilibrium in ternary mixtures containing water + ethanol + cogener has been modeled using parameters obtained from binary mixture data only. The congeners are substances that although present in very low concentrations, of the order of part per million, 10⁻⁶ to 10⁻⁴ mg/L, are important enological parameters [1] and [2]. In this work two predictive models, the PSRK equation of state and the UNIFAC liquid phase model and two semipredictive activity coefficient models: NRTL and UNIQUAC have been used. The results given by these different models have been compared with literature data and conclusions about the accuracy of the models studied are drawn, recommending the best models for correlating and predicting the phase equilibrium in this type of mixtures.     

Influence of solvents on the insertion of methacrolein into zirconacyclopropenes

The reaction of Cp₂Zr(L)(η²-Me₃SiC₂) (L = THF, py) with equimolar amounts of H₂C = CMe-CHO at room temperature depends strongly on the ligands L and the solvents that are used. With L = THF, in the THF solution the insertion product

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1 was isolated, whereas by conducting the reaction in n-hexane solution an alkyne substitution with 1,4-coordination of the methacrolein takes place and the binuclear complex [

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2 was obtained. In conttrast, with L = py (a stronger ligand) only a 1:1 ratio of 1 and 2 was observed in both THF and in n-hexane. At 50°C complex 1 was converted into 2 and the alkyne was eliminated quantitatively.

Complexes 1 and 2 were characterized by IR and NMR spectroscopical measurements and 1 by an additional X-ray structure determination.     

Isolation of a diketone species that is allylically bound to tungsten, and its relationship to a tungsten η-ketone complex

The diketone complex [W(CO)₂(η-C₅H₄Me){η³-

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(H)---C(O)---C₅Me₅}] (3) was isolated from the reaction of PhC₂H with a mixture of [Ni(CO)I(η-C₅Me₅)] and [W(CO)₃(η-C₅H₄Me)]⁻. Complex 3 contains an organic diketone fragment that is bound in a π-allyl fashion to a tungsten atom. It was fully characterized by standard spectroscopic techniques and by a single-crystal X-ray diffraction study. The relationship of complex 3 to a structurally characterized cyclopentadienyl tungsten η²-ketone species 1, and the likelihood that 3 and the methylcyclopentadienyl analog of 1 share common intermediates, are discussed.     

Structures of the mono-acid cations of 4-aminoazobenzene and its derivatives

Conflicting views exist on the structures of the mono-acid cations of 4-aminoazobenzene and its derivatives. The azonium structure (I) and the ammonium structure (II) have been separately upheld as correct, but detailed examination of spectroscopic data shows that both forms exist in solution as tautomeric equilibrium mixtures (I

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II).     

Kinetics of formation of intermediates in silver ion assisted aquations

There is kinetic evidence of the formation of [Co(NH₃)₅NCSAg₃]⁵⁺ in the interaction of [Co(NH₃]⁵NCS]²⁺ with Ag⁺ in aqueous solution, with pseudo-first-order formation rate constant k = 0.158 s⁻¹ for the forward reaction in the following equation at 25°C and [Ag⁺] in the range of 1.23–5.0 × 10⁻² mol dm⁻³ and 0.10 ionic strength (NaClO₄):

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Additionally, the formation constant, β₂, for [Co(NH₃)₅NCSAg₂]⁴⁺ has been determined to be log β₂ = 4.717. For the [Rh(NH₃)₅I]²⁺-Ag⁺ reaction there is evidence of an outer-sphere interaction with rate constants of k₂ = 670 dm³ mol⁻¹ s⁻¹ at 25°C and 0.10 ionic strength. This outer-sphere species undergoes further reaction to give the silver ion containing intermediates of the aquation reactions.     

Control factors for hydrogen-atom abstraction from organic molecules in cryogenic solids

Hydrogen-atom transfer from organic molecules to free deuterium atoms and to methyl radicals in cryogenic organic solids due to quantum-mechanical tunneling of C–H hydrogen was studied for elucidating the control factors for the reaction. The following differences were found in comparison with regular thermal reactions: (1) The rate of hydrogen-atom tunneling decreases with increasing number and length of alkyl chains attaching to C–H carbon to be hydrogen-abstracted. This is due to the increase of steric hindrance to the deformation of the chemical bonds of the C–H carbon. The abstraction accompanies the change of the chemical bonds for the C–H carbon from sp³ to sp², so that prevention of the deformation by the alkyl chains causes the increase of the thickness of the potential barrier for the tunneling. The tunneling rate therefore decreases. (2) The rate of abstraction increases with the energy released by the reaction. The energy is used to excite the vibrational states of product molecules, which accelerates the tunneling from the initial reactant state to the final product state.     

Influence of macroscopic and microscopic interactions on kinetic rate constants: I. Role of the extended DLVO theory in determining the kinetic adsorption constant of proteins in aqueous media, using von Smoluchowski’s approach

In the case of adsorption in an aqueous medium of a hydrophilic protein (e.g. human serum albumin (HSA)) onto a hydrophilic solid substratum such as a clean glass surface, one has to deal with a macroscopic-level repulsion between HSA and glass at (generally) the majority of orientations of the protein molecules, and also a microscopic-level attraction between HSA and glass at (generally) the minority of orientations of the protein molecules. The first phenomenon represents von Smoluchowski’s improbability of adhesion or adsorption and the second represents the probability of adhesion or adsorption [1]. Both contingencies have to be taken into account in determining von Smoluchowski’s net probability factor, f of the kinetic association constant, k_a, pertaining to protein adsorption. In the exceptional case where both the protein and the solid substratum are hydrophobically/hydrophilically and electrostatically neutral, f=1, and the k_a-value is only proportional to the diffusion coefficient of the protein [2]. In order to determine the contributions of both the macroscopic repulsion and the microscopic attraction pertaining to the kinetics of protein adsorption, an extended DLVO analysis (XDLVO) needs to be done on these interactions at all distances and at all protein orientations. The XDLVO analysis comprises the Lewis acid–base interaction energies as a function of distance, in addition to the Lifshitz–van der Waals and the electrokinetic interaction energies [2, 3, 4 and 5].     

Nuclear magnetic resonance studies for the chiral recognition of the novel chiral stationary phase derived from 18-crown-6 tetracarboxylic acid

Enantioselectivities observed in high-performance liquid chromatography (HPLC) with the novel chiral stationary phase (CSP-18C6I) derived from (+)-18-crown-6 tetracarboxylic acid (18C6H₄) were investigated by using nuclear magnetic resonance (NMR) spectrometry. The elution orders in CSP-18C6I, that is, the S-enantiomer of 1-(1-naphthyl)ethylamine (1-NEA) and the

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-enantiomer (S-form) of alanine-β-naphthylamide (Ala-β-NA) eluted prior to each corresponding enantiomer, were successfully explained on the basis of the apparent binding constants (K_a) of the enantiomers to the CSP moiety which were calculated from ¹H-NMR experiments. Detailed HPLC and NMR studies for the chiral recognition of racemic amino compounds with 18C6H₄ hosts showed that ¹H-NMR spectrometry is a useful technique for the investigation of the chiral recognition mechanism in HPLC. Additionally, it was found 18C6H₄ can be recommended as a useful chiral shift reagent for the enantiomeric excess determination by ¹H-NMR.     

Formation d''etats triplets du biacetyle dans sa reaction en phase gazeuse avec un plasma froid d''azote

The behaviour of the biacetyl molecule (BA) in a cold plasma, obtained by extraction of reactive species from a nitrogen plasma generated in a microwave discharge, is discussed. When the partial pressures of nitrogen and biacetyl are approximately equal (p_N2 ≈ 0.60 Torr, p_BA ≈ 0.55 Torr), the emission of the ³A_u---¹A_g transition of biacetyl is observed with a vibrational structure. On reaction of biacetyl with nitrogen cold plasma preferentially enriched in N₂(A³Σ⁺_u), an enhancement of the emission intensity of the phosphorescence of biacetyl is observed. The initiator of this transition is the triplet state BA(³B_u) which originates from an isoenergetic transfer from N₂(A³Σ⁺_u) according to the overall mechanism

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Chemistry of polyfunctional molecules-123. Reactions of BiBr3, SbI3 and AsI3 with LiN(PPh2)2; X-ray structure of a cyclophosphazene salt containing arsenic(I)

BiBr₃ or SbI₃ react at 20°C with LiN(PPh₂)₂ (1) to give elementary Bi or Sb and the P---P coupled phosphazene ligand Ph₂P---N=PPh₂---PPh₂=N---PPh₂ (2). The reaction of AsI₃ with 1 at room temperature formed yellow needles of the eight-membered heterocycle (3), whereas AsI₃ interacted at 80°C with 1 in the molar ratio of 1:3 to give elementary arsenic and 2. Treatment of AsI₃ and 1 at 20°C in a 1:2 stoichiometry yielded the seven-membered, cyclic arsenium(I) salt

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I·4THF (5·4THF), which was characterized by elemental analysis, conductivity, mass, IR and NMR spectroscopy and single-crystal X-ray structural analysis.     

Simple charge transfer complexes of some new and of some known heterocyclic compounds of selenium and tellurium

Charge transfer (CT) complexes (1:1) of 2,5-dihydrotellurophene and the 3-methyl and 3,4-dimethyl compounds with TCNQ and tetrachlorobenzoquinone (TCB) are reported. The organotellurium compounds failed to give complexes with p-dinitrobenzene (DNB). The variation of solid state (disc) conductivity with temperature and as a function of methyl substituents is considered. The complexes show semi-conducting behaviour and a consideration of these data, together with IR and UV spectroscopic data, in comparison with those for 1,3-dihydro-2-telluraindene given the following order of donor power with respect to TCNQ:

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With respect to a given donor, the order to acceptor power is TCNQ> TCB> DNB.

1,3-Dihydro-2-selanaindene forms a complex with TCNQ. The molecular ionisation potential of the selanaindene is 7.4 eV (by mass spectroscopy) and it has been shown that the compound may be electrochemically oxidized to materials such as C₈H₈SePF₆.

New quinoxalino-1-chalcogenacyclopentanes are reported; namely those derived from selenium, and for the 7,8-dimethyl series, those based on both selenium and tellurium. Their preparation and characterisation are described, and their chemistry shown to be strongly analogous to that of quinoxalino-1-telluracyclopentane. CT complexes of the new Se^II and Te^II compounds (1:1) are prepared with TCNQ which are believed to be strongly ionic.     

Liquid-phase Oppenauer oxidation of primary allylic and benzylic alcohols to corresponding aldehydes by solid zirconia catalysts

Hydrous zirconia and grafted zirconium 1-propoxide catalysts were found active in the Oppenauer oxidation of cinnamyl alcohol, geraniol and 4-tert-butylcyclohexanol (cis- and trans-). The most active hydrous zirconia catalysts were formed by calcining at 250–300 °C. Grafted zirconium 1-propoxide on silica gel and MCM-41 were active in the Oppenauer oxidation of geraniol with high selectivity to the desired citral product. However, over an acidic support such as AlMCM, the grafted zirconium 1-propoxide catalysed the dehydration and isomerisation of the alcohol, leading to low yield to citral. Also, furfural was found to be an efficient oxidant for the titled Oppenauer oxidation. Other solid catalysts such as γ-Al₂O₃, Na–Al₂O₃, zeolite beta and Mg/Al hydrotalcite showed only moderate catalytic activity and selectivity in the Oppenauer oxidation of geraniol. As compared to other solid catalysts, hydrous zirconia solid catalysts used in this work are active and selective towards the formation of desired carbonyl oxidation products; additionally, these solid zirconia catalysts are easy to prepare and recycle, and applicable to different alcohol substrates.

Graphical abstract

Hydrous zirconia calcined at 250–300 °C and grafted zirconium 1-propoxide solid catalysts were found to be efficient for the Oppenauer oxidation of cinnamyl alcohol, geraniol and 4-tert-butylcyclohexanol in toluene when furfural was used as the oxidant.

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Synthesis and characterisation of four- and eight-membered ring auralactam complexes

The reactions of the cyclo-aurated gold(III) dihalide complex [{C₆H₃(CH₂NMe₂)-2-(OMe)-5}AuCl₂] with N-cyanoacetylurethane [NCCH₂C(O)NHCO₂Et], 2-benzoylacetanilide [PhC(O)CH₂C(O)NHPh] and acetoacetanilide [MeC(O)CH₂C(O)NHPh], and [{C₆H₄(CH₂NMe₂)-2}AuCl₂] with acetoacetanilide in dichloromethane with excess silver(I) oxide gives the first examples of auralactam complexes, containing (O)---CHR′ four-membered rings. A single-crystal X-ray diffraction study on the complex [{C₆H₄(CH₂NMe₂)-2}A H(COMe)}] reveals similar structural features to related metallalactam complexes of platinum(II) and palladium(II). When a CDCl₃ solution of the complex [{C₆H₃(CH₂NMe₂)-2-(OMe)-5}A HCN}] is allowed to stand for 18 h, a novel dimerisation reaction occurs, giving the insoluble product [{C₆H₃(CH₂NMe₂)-2-(OMe)-5}Au{N(CO₂Et)C(O)CHCN}]₂·2CDCl₃, characterised by an X-ray structure determination. The dimer contains an eight-membered A

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ring.     

Chelating diphos ligands with inorganic backbones. Crystal structure of [PtCl2{(PPh2O)2SiPh2}]

The metallo-phosphaalkenes (η⁵-C₅Me₅)(CO)₂FeP=C(R)(SiMe₃) (Ia: R = SiMe₃, Ib: R = Ph) and MeO₂C---CC---CO₂Me undergo a dipolar [3+2]-cycloaddition to afford the metallo-heterocycles [(η⁵-C₅Me₅)(CO)

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=C(R)SiMe₃] (IIIa,b) with exocyclic P=C double bonds.