Electrogeneration of triplet states of intramolecular anthracene-amine systems

In the electron transfer between the cation radicals

of the amine moiety of four intramolecular anthra cene-amine systems and the anion radicals B^XXX of some heterocyclic and carbonyl compounds in acetonitrile/toluene, the triplet state of the anthracene moiety

is formed. As intermediates in this process, intramolecular and intermolecular triplet exciplexcs

or

and

or

are discussed.     

Laser flash photolysis of iodine-iodide mixture in hydroxylic solvent. Evidence for the existence of the radical anion I

The laser flash photolysis of iodine-iodide mixtures in alcoholic solvents produces transient species absorbing in the red and near infrared region with maxima at 740 and 590 nm. The 740 nm absorption band has already been attributed to the well known I

ion. In this work the 590 nm absorption band is assigned to the I

radical anion which presumably could be formed by the equilibrium reaction: I

+ I₃^- ? I

. The variations of the intensities of the 590 and 740 nm transient absorption bands as a function of I₃^? concentration, temperature and solvent, support this assignment. The kinetics of formation of I

and I

has been studied in solutions of tertiary butanol. An analysis of the experimental results shows that the I

ion could be formed via a mechanism involving an I

intermediate.     

The preparation of fluxional tetrahydrides, (R  H or Me) and their reactions with CO,ButNC or HBr

The cyclometallated monohydrides

(R  H or Me) react with NaOPrⁱ/PrⁱOH/H₂ to give fluxional tetrahydrides, probably

. These are highly fluxional having magnetically equivalent hydridic hydrogens, even at ---100°C. When treated with HBr,

, gives

and with CO it gives a mixture of complexes which are probably

(2 isomers) and

. When treated with Bu^tNC this tetrahydride undergoes similar reactions but another (major) product is formed which appears to be binuclear and fluxional and is probably of type

, with four bridging hydrogens.     

Electrokinetic phenomena in porous membranes: Determination of phenomenological coefficients and transport numbers

Electrokinetic phenomena in porous membranes were studied in the framework of the linear thermodynamics of irreversible processes. Phenomenological coefficients of two commercial porous membranes were determined. The variation of these coefficients with the different concentrations of NaCl used was also studied. Onsager's reciprocal relationship between cross-coefficients holds within the limits of experimental error.Membrane potentials were measured at concentrations ranging from 10^?3M to 75 X 10^?3M. The apparent transport number of the cation,

, was calculated from the diffusion potential expression. An electrometric method was used to obtain the true cation transport number,

, and the water transport number,

, for different solution concentrations, ranging from 15 x 10^?3M to 75 x 10^?3M. The true transport number of the cation,

, was also determined, taking into account water transport across the membrane. A good agreement was found between

and

values.     

ESR spectra and electronic structure: some recent examples.

Results of ESR studies are presented for a number of radical ions selected from several classes of compounds of current interest. The strikingly different hyperfine data for the radical cations of 1,6:8,13-propane-1,3-

and 1,6:8,13-ethane-diylidene-[14]annulene

demonstrate the effect of an interplay of homoconjugative, inductive and hyperconjugative perturbations. The unusually stable radical cations of N,N′-dimethyl-

and N,N′-trimethylene-1,6:8,13-bisimino[14]annulene

should be regarded as N-centered radicals with an N-N 3-electron σ-bond. Despite similar geometries of [2.2]paracyclophane

, its 1,1,2,2,9,9,10,10-octa-fluoro-derivative

and its 1,9,-diene

, the corresponding radical anions strongly differ in their electronic structure. An unexpected conformatinal interconversion is observed for the radical anion of

. Electron acceptors, such as tetracyanoquinodimethane (TCNQ;

) and its areno analogues, and electron donors, represented by tetrathiafulvalene (TTF;

) and compounds containing the TTF system, form salts exhibiting high electronic conductivity (“organic metals”). ESR spectra of the radical anions and trianions of these acceptors and the radical cations of these donors provide detailed information about the spin distribution in the respective species.     

Vibronic interaction between nπ and ππ states and phosphorescence of Norharmane

Solvent effects on phosphorescence and excitation spectra and its polarization characteristics indicate that the two major spin-orbit coupling mechanisms through which the ³ππ^* state of Norharmane acquires dipole-allowed character via nπ^* states are:

     

Excited-neutral-metastable SO2 formation in the , O3-olefin-SO2, and active nitrogen-SO2 systems

Long-liied (τ > 10^?3 s), electronically-excited (E * > 4 eV) neutral metastables, whose formation was attributed to the presence of SO₂, were observed in the three titled systems. Their possible identity as collisionally-accessed metastable states of the normal

, cyclic

, or superoxide

isomers of SO₂ is discussed.     

Diversity of the gramicidin a spatial structure: two-dimensional 1H nmr study in solution

Theoretical consideration reveals a unique relationship between NMR spectral parameters and possible types of the gramididin A spatial structure. By means of two dimensional NMR spectroscopy four distinct species were detected simultaneously in ethanol solution. Comparison of experimental data and theoretical conclusions demonstrates that species 1 and 2 are left-handed parallel double helices

differing in relative arrangement of the two polypeptide chains within the dimers, species 3 is left-handed antiparallel double helix

, and species 4 is a mirror image of species 1, i.e. right-handed parallel double helix

. The results are compared with those on spatial structures of the peptide in complex with cesium (right-handed antiparallel double helix

) and of the gramicidin A transmembrane ionchannel (N-terminal to N-terminal single-stranded dimer

).     

Overlap contribution to internal conversion coefficients of the 14.4 keV M1 transition in 57Fe

It is suggested that while evaluating contact charge densities from internal conversion coefficients it is important to consider overlap effects. Ratios of the internal conversion coefficients

and

are evaluated as a function of interatomic separation for Fe³⁺ in an octahedral arrangement of Br^? ions.     

Synthesis and intramolecular charge-transfer interaction of o-tropyliobiphenyl tetrafluoroborates

A series of o-tropyliobiphenyl tetradfluoroborates

has been synthesized. Evidences are presented to show that

exhibit strong intramolecular charge-transfer interaction between tropylium ion and remote aryl ring. The structure of

was determined by single crystal X-ray diffraction study.     

Synthese de la phenyl-2-dimethyl-4,5-phosphorine a partir du benzyl-1-dimethyl-3,4-phosphole

1-Benzyl-3,4-dimethylphosphate

-$\text{1}$ is converted into 2-phenyl-4,5-dimethyl-λ₃-phosphorin

-$\text{2}$ through 1,2-dihydro-λ₅-phosphorines

$\text{3}$ and

$\text{s}$.     

The composition of the evolved gases from the thermal decomposition of certain metal sulfates

By the use of TG—MS, the thermal dissociation of anhydrous CuSO₄ and Al₂(S0₄)₃ was found to proceed according to the reactions:

followed by the reactions:

No SO₃ was indicated in the dissociation of alunite. The sulfate ion appears to dissociate by at least two different mechanisms although the parameter which controls the mechanisms has not been elucidated.     

The preparation of perfluorinated esters of fluorine containing tertiary alcohols

The reaction of an aromatic lithium reagent, LiR, with a perfluoroacid anhydride (RfCO)₂O, in ether solution at low temperatures, produces esters of composition

in addition to the expected ketone

. Mixed esters of composition

may be prepared by starting with a ketone

and reacting with a lithium reagent LiR followed by perfluoroacid anhyride (RfCO₂O. Hydrolysis of the esters provide a convenient route to trertiary alcohols of composition Rf(R) ₂COH.     

A direct synthesis of 1,3-bis(bromomagnesio)propane

Careful addition of 1,3-dibromopropane

to magnesium in Et₂O yields 1,3-bis(bromomagnesio)propane

which is purified via “magnesacyclobutane”

. Reactions of

with H₂O, CO₂, HgBr₂ and Me₃SnCl are reported. MgBr₂ catalyses the decomposition of

to allylmagnesium bromide

.     

Electrocyclic reactions : Stereochemistry of the triene electrocyclization

Four trienes of known stereochemistry have been prepared and their thermal cyclization studied to ascertain the general stereochemistry of thermal triene electrocyclic reactions. A mixture containing (Z)-1,2-dicyclohexenylethylene was obtained by semihydrogenation. Spectra evidence for thermal cyclization of the triene was obtained, but inability to isolate pure materials canceled plans for stereochemical study.A stereoselective synthesis for (E,Z,E)-2,4,6-octatriene was devised and a pure sample was cyclized thermally to give a 5,6-dimethylcyclohexadiene. Oxidative cleavage of this diene gave meso-2,3-dimethylsuccinic acid. Pure samples of (Z,Z,E)- and (Z,Z,Z)-2,4,6-octatrienes were prepared and found to interconvert thermally at 110°. Cyclization of the equilibrium mixture occurred at 178° to give a 5,6-dimethylcyclohexadiene which gave rac-2,3-dimethylsuccinic acid upon oxidative cleavage. Evidence is presented to suggest that the (E,Z,Z) isomer is the actual reactant undergoing cyclization. Both cyclohexadienes were shown to undergo a 1,5-hydrogen shift to form 1,6-dimethyl-1,3-cyclohexadiene.Rates of the electrocyclic reactions were measured in pentane solution, and thermodynamic activation parameters were ascertained. The results are: (E,Z,E) k(132°) = 4·45 × 10^?5 sec^?1, ΔH

= 28·6 kcal/mole and ΔS

= ?7 eu; (E,Z,Z)+(Z,Z,Z) k(178°)= 1·53 × 10^?5 sec^?1 or (E,Z,Z) k(178°) = 2·13 × 10^?5 sec^?1, ΔH

= 32 kcal/mole, ΔS

= ?9 eu; cis-5,6-dimethyl-1,3-cyclohexadiene (1,5-H shift), k(178°) = 1·77 × 10^?5 sec^?1, ΔH

= 33 kcal/mole, ΔS

= ?7 eu; trans-5,6-dimethyl-1,3-cyclohexadiene (1,5-H shift), k(178°) = 7·7 × 10^?6 sec^?1, ΔH

= 36 kcal/mole, ΔS

= ?3 eu.     

On the nature of the active centres in the initial stages of methacrylonitrile anionic polymerization—I: Spectral studies

The active centres in the initial stage of methacrylonitrile anionic polymerization have been studied by means of electronic and i.r.-spectra as well as by use of model compounds. The attachment of the first monomer unit to the initiator causes formation of the carbanion

, characterized by an absorption band at 2020–2055 cm^?1. Addition of more monomer units leads to the appearance of a new band at 2100 cm^?1, due to the group

. The appearance of a new band at 2260 cm^?1 and the shift of the band at 2020–2055 cm^?1 towards higher frequencies, as the number of adjacent monomer units is increased, is explained by interaction of the active centres with the nitrile groups of the polymer chain.     

Enthalpies de formation du nitrate d'yttrium hexahydraté et de l'ion Y3+

The dissolution enthalpies of yttrium and hexahydrated yttrium nitrate in nitric acid at different concentrations have been measured and the following enthalpies have been determined:

     

Synthesis of (±)-lineatin,the unique tricyclic pheromone of Trypodendron lineatum (olivier)

(+-)-3,3,7-Trimethyl-2,9-dioxatricyclo[4.2.1.0^{4, 7}]noname

and (+-)-3,3,7-trimethyl-2,9-dioxatricyclo[3.3.1.0^{4, 7}] nonane

were synthesized. The latter was shown to be (+-)-lineatin, an ambrosia beetle pheromone.     

Solvolysis of bridgehead chlorides with strained bridgehead double bond.

Product study and kinetic data of the solvolysis of the bridgehead chlorides (

) and (

indicate the neighboring group participation of the strained bridgehead double bonds.