Non-rigid molecules : III. Sigmatropism in organometalliic complexes of indene

The effects of π system geometry upon the transition states for sigmatropism in five-membered rings is discussed semi-quantitatively using the PMO theory. Comparison of the results with measured activation energies suggests that the [1, 3] averaging in organometallic indene complexes proceeds via sequential [1, 2] shifts in all those cases examined.     

Trimethylsilyl-substituted diazoalkanes : I. Trimethylsilyldiazomethane

Trimethylsilyldiazomethane was prepared by the action of aqueous KOH on nitroso-N-(trimethylsilylmethyl)urea. The spectroscopic properties of this stable, greenish-yellow liquid which can be isolated by gas chromatography are discussed. Its reaction with acetic acid gives the expected CH₃CO₂CH₂SiMe₃ in addition to SiC cleavage products, CH₃CO₂CH₃ and CH₃CO₂SiMe₃. Products of the 1,3-dipolar addition of Me₃SiCHN₂ to activated olefins were not very stable, and only the adduct with acrylonitrile was isolated as a pure material Trimethylsilyldiazomethane undergoes Me₃SiCH transfer to olefins, giving trimethylsilyl-substituted cyclopropanes, in the presence of CuCI in benzene, but other products are formed as well. Thus such a reaction with cyciohexenegave anti-7-trimethylsilylnorcarane (65%), syn-7-trimethylsilylnorcarane (7%), cis- and trans-l,2-bis(trimethylsilyl)ethylene (9% and 13%, respectively), and an unidentified Me₃SiCH trimer (2.3%).     

Metal complexes of fluorophosphines : III. Some oxidative addition reactions of a rhodiumtrifluorophosphine complex

Some oxidative addition reactions of (CH₃)₅C₅Rh(PF₃)₂ with various iodine compounds are described. Iodine reacts with (CH₃)₅C₅Rh(PF₃)₂ in benzene at room temperature to give the deep red crystalline diiodide (CH₃)₅C₅Rh(PF₃)I₂. The perfluoroalkyl iodides R_fI (R_f = CF₃, C₂F₅, n-C₃F₇, and n-C₇F₁₅) react with (CH₃)₅C₅Rh(PF₃)₂ in benzene at room temperature to give the orange to deep red (CH₃)₅C₅Rh(PF₃)(R_f)I (R_f = CF₃, C₂F₅, n-C₃F₇, and n-C₇F_l5). The IR and proton and fluorine NMR spectra of these new (pentamethylcyclopentadienyl)rhodium-trifluorophosphine complexes are discussed.     

Metal carbonyl-trifluorophosphine systems : X. Mono-and triruthenium carbonyls

Triruthenium dodecacarbonyl reacts with high pressure PF₃ or with PF₃/CO mixtures to yield two series of compounds. At high PF₃ pressures, the mononuclear species Ru(PF₃)_x(CO)_5−x (x = 5, 4 and 3) are the main products with only traces of Ru(PF₃)₂(CO)₃ and Ru(PF₃)(CO)₄ being found. With high carbon monoxide pressure and less PF₃, the species Ru₃(PF₃)_y(CO)_12−y (y = 0–6) are the main products. It is seen that Ru₃(CO)₁₂ can have up to six CO groups replaced sequentially before the cluster is broken followed by the formation of the mononuclear species. The evidence shows that the Ru(PF₃)_x(CO)_5−x species are stereochemically non-rigid.     

Etudes photochimiques—XIV : Photoreactions des methylisothiazoles

Photorearrangement of methylisothiazoles proceeds via a zwitterion and the amount of rearranged products increases with solvent polarity. When irradiated in the presence of primary amines, 3-methylisothiazole which is the less isomerised, and 5 methylisothiazole give charge transfer complexes. The amine cation radical is hydrolysed to an aldehyde. 4-Methyl isothiazole does not lead to a charge transfer complex.     

Massenspektroskopische fragmentierungsreaktionen—III : Das scheinbar anomale verhalten von 3-hydroxytetrahydropyransystemen

Tetrahydropyran derivatives may lose C-2 together with a substituent from C-3 accompanied by ring contraction. This explains why, e.g., compounds derived from 3-hydroxytetrahydropyran sometimes fragment in a manner expected for an isomeric tetrahydrofuran system. The prerequisities for this rearrangement and its mechanism are discussed.     

Rotational isomerism—XIII : Rotational isomerism in furfuraldehyde

The equilibrium between the cis and trans isomers of furfuraldehyde has been studied by measuring the stereospecific coupling constants between the aldehyde and ring protons in various solvents. These values when combined with the observed values of the couplings in the individual conformers at low temperatures give the energy difference between the cis and trans forms in these solvents. These values together with other previous measurements demonstrate the large solvent effect on this equilibrium. E(cis)-E(trans) is +1·5 kcals/mole in the vapour, much smaller in non-polar solvents (+0·3 kcals/mole in CF₂Cl₂), ca 0 in CHCl₃ and becomes negative in polar media (−1·0 kcals/mole in the pure liquid). This solvent dependence is given a quantitative explanation in terms of a known theory of solvation.     

Nitroxydes—XLVII: Nitroxydes isoquinuclidiniques

5 and 7 substituted 1,3,3-trimethyl isoquinuclidines are prepared by the action of ammonia on piperitenone and 4-methyl piperitenone. Reduction of 1,3,3-trimethyl 5-isoquinuclidone, and the different alcohols obtained are described. The nitroxydes obtained by oxidation of these amines exhibit long range couplings.     

Organogermanium compounds : II. Reduction of organic halides with hydrogermanes

The scope of the reduction of organic halides with trialkylgermanes under homolytic condition has been studied. Germanium hydrides can reduce polyhaloalkane without catalysts under mild conditions, the homolytic mechanism being, however, established for the uncatalyzed reduction. The observed orders of reactivity and selectivity in the reduction are consistent with a radical chain mechanism involving free germyl radicals. Some synthetic applications are described.     

Low-frequency vibrations of molecular solids: XV. Globular molecule 1,2-dichloroethane

The far infrared and Raman spectra of polycrystalline 1,2-dichloroethane and 1,2-dichloroethane-d₄ for the low temperature modification have been measured from 450 to 33 cm⁻¹ at various temperatures from −100 to −182°C. Raman spectra of the high temperature crystalline modification for both samples were also investigated. The Raman data are in conflict with those previously reported. Assignments are made for the lattice vibrations in terms of the crystallographic unit cell C_2h⁵ (P_21/c) with two molecules per unit cell. The spectra of the high temperature modification are consistent with those expected for orientationally disordered crystals.     

Isochinolinio-amidate : Synthese und einige reaktionen von N-acyl- und N-sulphonyl-derivaten

Three methods have been developed for the synthesis of N-acyl- and N-sulfonyl-aminoisoquinolinium chlorides (6) and the corresponding dipolar bases (7): (1) ring closures of N-acyl- and N-sulfonyl-N-{2-[β-(2,4-dinitranilino)vinyl]benzylidene}hydrazines(5β), (2) acylation of N-aminoisoquinolinium chloride (6a) and (3) transacylations of N-(2-isoquinolinio)-ethoxycarbonylamidate (7i). IR and NMR spectra as well as some reactions of compounds 7 are discussed.     

Through-bond vs through-space interactions : The stabilization of carbonium ions

The solvolysis technique is suggested as an investigational tool for the possible opposing effects of through-bond and through-space orbital interactions. Existing data indicate, however, that such effects are negligible. A rationalization of the results is presented.     

Mechanisms involved in stannane generation by aqueous tetrahydroborate(III): Role of acidity and l-cysteine

The role played by acidity (0.01–5 mol L^− 1 HNO₃) and l-cysteine (0.1–0.2 mol L^− 1) in the formation of stannane by reaction of Sn(IV) solution with aqueous tetrahydroborate(III) (0.05–0.2 mol L^− 1), has been investigated by continuous flow hydride generation coupled with atomic absorption spectrometry using a miniature argon–hydrogen diffusion flame as the atomizer. Different mixing sequences and reaction times of the reagents were useful in the identification of those processes which contribute to the generation of stannane in different reaction conditions, both in the absence and in the presence of l-cysteine. The lack of stannane generation at high acidities is due to the formation of Sn substrates and hydridoboron species which are unreactive. The capture of the stannane in solution, following its ionization to SnH₃⁺ from already formed stannane, does not play any role. While the presence of l-cysteine, does not affect the generation efficiency at lower acidities, it expands the optimum range of acidities for stannane generation to higher values. This effect can be addressed to both the buffering capacity of l-cysteine and to the formation of Sn-(l-cysteine) complexes, while the formation of (l-cysteine)–borane complexes do not play a significant role. Formation of Sn-(l-cysteine) complexes also appears to be useful for stabilization of tin solution at low acidities values.     

Chemistry of leucomycin-X: Conformational studies on leucomycin

The conformation of leucomycin, a macrolide antibiotic with a 16-membered ring lactone, was examined in solution by IR, NMR and CD spectral analysis. The IR reveals that the five hydroxyls are all involved in intramolecular H-bonding. The NMR of the 16-membered ring lactone forming the aglycone shows that the acetyl-carbonyl at C-3, the allylic proton at C-11 and the aldehyde proton are in close proximity on the lactone ring. CD studies suggest that the conformation of the 16-membered ring lactone, especially around the lactone, is mobile and solvent dependent.     

MO-berechnungen an heterocyclen—VII : Tautomerieprobleme an substituierten 1,3,8-triazaindolizinen

The electronic spectra of some derivatives of 5-hydroxy-7-methyl-1,3,8-triazaindolizine have been calculated with the PPP-procedure. With the electronic spectra and heats of atomization the tautomeric structures of the compounds 6-ch]or-5-hydroxy-7-methyl-1,3,8-triazaindolizine, 6-brom-5-hydroxy-7-methyl-1,3,8-triazaindolizine, 6-carboxy-5-hydroxy-7-methyl-1,3,8-triazaindolizine, 2-carboxy-5-hydroxy-7-methyl-1,3,8-triazaindolizine, 2-mercapto-5-hydroxy-7-methyl-1,3,8-triazaind and 5-amino-7-methyl-1,3,8-triazaindolizine are discussed. The possible structures of the compounds 5-hydroxy-7-methyl-1,3,8-triazaindolizine, 5-hydroxy-7-methyl-1,2,8-triazaindolizine and 5-hydroxy-7-methyl-1,2,3,8-tetrazaindolizine depending on the pH-value of the solution have been investigated.     

Dual-wavelength spectrophotometry: Part III. Determination of arsenazo I in arsenazo III

A simple rapid spectrophotometric method for the determination of arsenazo I in the presence of large amounts or arsenazo III by means or a dual-wavelength method is discussed. By proper selection of the combination of two wavelengths, γ1 = 502.0 nm and γ2 = 575.3 nm, arsenazo III can be masked instrumentally even when its concentration varies. By this method about 0.5– 40%of arsenazo I in arscnazo III can be determined very easily and accurately.