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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Investigation of the 2B2 state of H2O+ using valence-bond techniques

Ab initio valence-bond calculations have been performed on the low-lying states of H₂O⁺, with special attention being focused on the

²B₂ state of the ion. The calculated potential energy surface for the

²B₂ state is in qualitative agreement with several previously published molecular orbital calculations in predicting an equilibrium angle of about 60°. This prediction is, however, inconsistent with the most recent interpretation of the high-resolution photoelectron spectrum of H₂O. Examination of the potential energy surfaces for geometries which have been distorted from C_2v symmetry indicates that the

²B₂ and òA₁ states are strongly coupled by the asymmetric stretching motion of the molecular ion. The presence of such a coupling supports the interpretation of the H₂O photoelectron spectrum which invokes excitation of the asymmetric stretching vibration of the ion.     

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.     

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.     

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.