Synthesis of polysaccharides. Glucorhamnan

The regular heteropolysaccharide glucorhamnan

was obtained by polycondensation of 3-0-acetyl-4-0-(2,3,4-tri-0-acetyl-6-0-trityl-β-D-glucopyranosyl)-1,2-0-(1-exo-cyanoethylidene)-β-L-rhamnopyranose catalysed with triphenylmethylium perchlorate.     

Abnormal g tensor and multiconfigurational ground state of

The shift of g_lj = 2.0094 in

(geometry D_3d, state ^2A_2u) from 2.0023 is too large to be rationalized with theories of the g tensor based on a single-configurational ground state. This abnormality can be explained with a multi-configurational ground state representing spin polarization.     

The transformation using the soft NO⊕-species

The reaction of NaNO₂ in acidic solution with thiocarbonyl compounds has been studied. Secondary- and tertiary thioamides, 1-benzyl-hexahydro-2H-azepine-2-thione, 5-ethyl-5-phenyl thiobarbituric acid, certain thiourea derivatives, 2H-1-benzopyran-2-thione, O,O-diphenyl-thiocarbonic ester, O,S-diphenyl-dithiocarbonic ester, N,N-dimethyl-S-phenyl-dithiocarbamatic ester, N-ethyl-N-phenyl-O-ethyl-thiocarbamatic ester are all converted into the corresponding carbonyl-analogues. 4,4′-Bis (dimethylamino)-thiobenzophenone (Michler's thioketone) gives 3-nitro-4,4′-bis (dimethylamino)-benzophenone at room temperature. At (?10 °C)-(?5 °C) the expected oxo compound is obtained as the main product together with 4-(N-nitroso-methylamino)-4′-(dimethylamino)-benzophenone.     

Tiazenido complexes with M = Mo or W and R = aryl OR alkyl

The preparation, structure and some properties of compounds

(M = Mo, W; R = aryl and R′ = aryl or alkyl) are reported. Temperature dependent ¹³C NMR spectra show that for R ≠ R′ = aryl the complexes are fluxional, but not when one of the R groups is an alkyl group. The fluxional mechanism involves an interchange of the two CO groups via Berry type pseudorotations.Mass spectrometric measurements show the formation of nitrene type species [(η⁵-C₅H₅)(CO)_nM=NR]⁺ with n = 0, 1, 2.     

Sur une nouvelle interaction intramoléculaire attractive influencant les équilibres conformationnels de Σ-4 cyclohexanones

The structural study of cyclohexanones with polar substituants in the γ position

shows:(1) lack of solvent effect on the conformational equilibria, giving a result which differs from those already obtained from α halogeno cyclohexanones(2) the predominance of the axial conformation due to syn diaxial attractive interactions.This work has been done by means of model compounds with a fixed conformation, synthesised by chlorination of corresponding Σ-4 cyclohexanones in α or αα' positions; their structural study gives supplementary proof of the existence of syn diaxial attractive interactions in the studied molecules.     

Mechanism of thermal energy charge transfer reactions: + N2. Analysis of isotopic data

The

+ N₂ charge transfer reaction has been studied in an ICR spectrometer using both ¹⁴N₂ and ¹⁵N₂. The N⁺/N₂⁺ branching ratio was measured from the zero collision limit (ca. 1 × 10^?5 torr total pressure) to collisional saturation (ca. 1 × 10^?3 torr total pressure) for He/N₂ ratios of 5, 10, 50 and 100. The data were analyzed by solving exactly the kinetic equations and the associated power absorption equations. A positive pressure dependence in the N⁺/N₂⁺ branching ratio was observed indicating some N⁺ is formed from collisional dissociation of excited

ions. Comparison is made with recently published data from other groups and previously published data from this laboratory.     

Theoretical study of the o-methyl substituent effect in hydrogen bonds

The relatively large differences in D_e and R_e obtained at the STO-3G level for hydrogen bonded dimers of water, methanol and dimethyl ether, and which correlate monotonically with atomic charges, are strongly attenuated with extended basis sets, and relationships among D_e,R_e, and electron populations are reversed. Ratios of D_eR_e products for pairs of proton donors (acceptors) with a common acceptor (donor), however, are constant for a given basis set.     

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.     

Spin trapping chemistry of sodium 2-sulfonatophenyl t-butyl nitrone . a negatively charged water-soluble spin trap

A new water-soluble negatively charged spin trap, sodium 2-sulfonatophenyl $\text{t}$-butyl nitrone is described.     

Vibrational rate enhancement in the X(=Cl,Br) + H2 HX + H reactions

The effect of a microwave discharge on the rae of production of HBr in the H₂/Br₂ system was found to be similar to that observed for the H₂/Cl₂ system. The interpretation of a large vibrational enhancement on the X(=Cl, Br) + H₂ reactions is in agreement with trajectory calculations for these reactions. The criteria of endothermicity and of activation energy as a measure of the role of internal excitation are examined and shown to be useful under different reaction conditions.     

Alternativ-Liganden VII1: Chelatkomplexe des typs (Me = CH3; X = CH3, Cl)

Chelate complexes of the type (CO)₄M$\text{nPMe}{}_2\text{CH}{}_2\text{Ch}{}_2\text{S}$iX₂ (X = Me, Cl) have been prepared from Na[Mn(CO)₅] and HMn (CO)₅, respectively, by two-step reactions with the ligands Me₂PCH₂CH₂SiX₂R′ using alkali salt, amine or HCl elimination. (CO)₄M$\text{nPMe}{}_2\text{Ch}{}_2\text{CH}{}_2\text{S}$iCl₂ is also obtained by cleavage of Mn₂(CO)₁₀ with Me₂PCH₂CH₂SiCl₃. IN the case of HMn (CO)₅ the intermediates (CO)₄Mn (H) L [L = Me₂PSiMe₃, Me₂PCH₂CH₂SiMe₂ (NMe₂), Me₂PCH₂CH₂SiCl₂ (NMe₂] can be isolated. The new compounds were identified by analytical and spectroscopic (IR, PMR, MS) methods.     

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.     

Synthese de composes a liaison MIVBmercure. Precurseurs d'especes monovalentes (germynes), et bivalentes (germylenes), de radicaux centrometalles et d'intermediaires

Polynuclear germylmercury compounds are obtained from the reaction of organohydrogermanes Ph_nGeH_4?n or digermanes Ph_2nGe₂H_4?n (n = 1, 2) with dialkylmercury R₂Hg. Di- or tri-mercurated geminal polygermates thus synthesized generally present a low stability and undergo thermal- or photo-decompositions leading to the corresponding monovalent (germynes), divalent (germylenes) or, trivalent (germanium centered radicals) species and also to intermediate

biradicals which could be considered as limit forms of germanium doubly-bonded compounds

. Such intermediates have been chemically and spectroscopically characterized.Extension of these reactions to the silicon analogs met with difficulties, and thus previously observed differences between silicon and germanium chemistry were confirmed.     

Experimental and ab initio evidence for preferred syn-conformation of thionyl amines, , X = H,CH3, and C6H5

The conformational syn—anti problem with respect to the

bond in thionylamines,

, has only partially been solved for X = H and CH₃ [1, 2]. By providing new experimental material for C₆H₅NSO and p-FC₆H₄NSO (vibrational spectra, low-resolution microwave spectra, dipole moment determinations) and by performing ab initio calculations for HNSO and CH₃NSO it is shown that these two molecules are exclusively syn conformers The experimental data here presented strongly suggest the same conclusion for C₆H₅NSO. The result is consistent with a previous investigation by van Woerden and Bijl-Vlieger [3] comprising 13 mono- and polysubstituted sulfinylanilines.