Isolation and structure of [HC[CH(SiMe(3))(SnMe(3))](2)](+): a remarkably stable sec-alkyl cation

The reaction of the tin-substituted propene Me3Sn(R)CHCH=CHR (R = SiMe3) with MCl4 in dichloromethane in the presence of Me3SnCl gives the first examples of isolable sec-alkyl carbocation salts, [HC{CH(R)SnMe3}2]+M2Cl9- (M = Zr, Hf). The compounds are thermally stable and, unlike previously isolated trialkyl carbocations, do not require superacidic media or weakly coordinating anions for stability. The crystal structure and DFT calculations suggest polarization of the Sn substituents and hyperconjugation as the reason for the unexpected stability. The stabilizing effect of tin is significantly stronger than that of Si. The carbocations are effective initiators for the polymerization of isobutene, isoprene, and alpha-methylstyrene.     

The analysis of C4–C11 hydrocarbons in naphtha and reformate with a new apolar fused silica column

This paper deals with the separation of alkanes, naphthenes, and aromatic compounds in naphtha and reformate, on a newly developed apolar high resolution GC column. The selectivity of this apolar phase has been compared with those of squalane, DB-1, and SE-30. A total of 95 hydrocarbons were reliably identified, mostly by GC-MS. Repeated measurements of Kováts retention indices are presented as evidence for the reproducible manufacture of fused silica columns coated with this phase.     

Mechanism of vinyl chloride polymerization

An overall mechanistic scheme for the suspension polymerization of vinyl chloride is presented. The process can be resolved into five discrete stages, each of which presents a unique environment for the interaction of the systems parameters. It is shown that the surface area of the polymer formed during the reaction is not a major factor in autoacceleration and that the increase of kinetic chain length with conversion is due to a radical dilution effect. The latter is a direct result of the difference in rates between polymerization and radical formation, the former being greater. The increase of the initial polymerization rate and the reduction of autoacceleration brought about by chain transfer agents can be explained by the lower diffusion rate and greater bulkiness of the chain transfer agent radical relative to that of the monomer radical. The chaintransfer agent CBr₄ is preferentially absorbed by PVC from solution in vinyl chloride. With lauryl peroxide as initiator it is shown that the “hot spot” is the result of a build-up of initiator in the monomer caused by its exclusion from the polymer phase. Vinyl chloride was found to dissolve 0.03% PVC at ambient temperature and to have no effect on the decomposition rate of lauryl peroxide.     

Fluordiazadiphosphetidine, 11. Mitt.: Eine neue Methode zur Herstellung der doppelt zwitterionischen Verbindung (CH3N)6P4F8

A new synthetic route for the preparation of the betain-like compound (CH₃N)₆P₄F₈ from (CH₃NPF₃)₂,N-methyl-hexamethyldisilazane andN,N-dimethyl-urea has been found. The steps of this multi-stage reaction could be rationalized to a far extent.

10. Mitteilung:Kubjacek M., Utvary K., Mh. Chem.112, 305 (1981).     

Alkyl and stannyl radical generation by CSn and SnSn bond dissociation in photolytically excited peralkylated tristannanes as studied by ESR and 119Sn-CIDNP

Tristannanes used as photochemical precursors for the synthesis of organic compounds react via triplet states followed by homolytic CSn and SnSn bond scission.     

Engineered protein cages for nanomaterial synthesis

Self-assembled particles of genetically engineered human L subunit ferritin expressing a silver-binding peptide were used as nanocontainers for the synthesis of silver nanoparticles. The inner cavity of the self-assembled protein cage displays a dodecapeptide that is capable of reducing silver ions to metallic silver. This chimeric protein cage when incubated in the presence of silver nitrate exhibits the growth of a silver nanocrystal within its cavity. Our studies indicate that it is possible to design chimeric cages, using specific peptide templates, for the growth of other inorganic nanoparticles.     

Investigations on diazo compounds and azides- LXII.: Synthesis and reactions of a-diazo phosphonates with a conjugated 1,3-diene unit

α-Diazo phosphonates with a conjugated 1,3-diene unit are synthesised by the Bamford-Stevens reaction ($\text{2}$ →$\text{4}$→$\text{3}$). They undergo [4+2]-cycloadditions with the dienophile $\text{5}$ to form the tetrahydrotriazolopyridazines $\text{8}$, which possess an unchanged diazo group. In contrast, dimethyl acetylenedicarboxylate ($\text{9}$) reacts exclusively with the diazo dipole of $\text{3}$ to yield the 3H-pyrazoles $\text{10}$, which rearrange to $\text{11}$ by sigmatropic PO-shifts and hydrolyse to form $\text{13}$. The diazo compound $\text{3b}$ isomerises to the pyrazole $\text{16}$ when heated in benzene.     

Der massenspektrometrische Verlust von Vinylalkohol aus 1-Amino-3-aryloxy-2-propanolen. 24. Mitteilung über das massenspektrometrische Verhalten von Stickstoffverbindungen

Loss of vinyl alcohol from 1-amino-3-aryloxy-2-propanols under electron impact Under electron impact compounds of type 1 (see Scheme 1) split off 44 mass units from the molecular ion. This unusual reaction was studied using derivatives and deuterium labelled compounds. It could be demonstrated that for this fragmentation reaction 16 is the important structural feature from which H₂(C3)?C(2)HOH (44 mass units) is lost. The preferred reaction mechanism involves a transition state in which four members of the side chain are involved (Scheme 2, mechanism 2).     

Beitrag zur Massenspektrometrie substituierter α, ω-Alkandiamine. 29. Mitteilung über massenspektrometrische Untersuchungen

Contribution to the mass spectrometry of substituted α,ω-alkane diamines The main mass spectral fragmentation pattern of compounds of types 1 to 4 is discussed. After loss of C₆H₅ · CH₂ · from the molecular ion the acid correspondin to the N,N-disubstituted residue is splitted off. The mechanism of this fragmentation reaction depends on the member of CH₂-groups between the two nitrogen atoms (Schemes 1 and 3) and on the substitution pattern of both nitrogens (Scheme 2).     

Peroxides of higher aliphatic ethers

The oxidation of higher aliphatic ethers with oxygen at 50° yields two peroxides as the main oxidation products for each ether, namely a dihydroperoxy-dialkyl ether and a dihydroperoxy-dialkyl peroxide. The mass spectra of these compounds are recorded and the main fragmentation pattern is discussed.