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The radical anions of a series of para -silyl substituted N,N -dimethylanilines; p 0SiH n Me 3− n C 6 H 4 NMe 2 ( n = 0−3) have been studied by electron spin resonance spectroscopy. When n = 0 or 1 the primary radicals may be generated by either electrolytic or metal reduction. For n = 2 or 3 reduction with potassium immediately gives secondary paramagnetic species resulting from loss of hydride from silicon. Primary radicals for the n = 2 or 3 compounds may be obtained electrolytically. The ESR spectra show increasing spin delocalization into the silyl group as n increases, to the point that the spin distribution in the p -SiH 3 compound approaches that of p -nitro- N,N -dimethylaniline radical anion. A tentative analysis of the secondary and tertiary spectra is given. The results, coupled with CNDO/2 calculations for the radical anions, indicate that the primary interaction between silicon and the aromatic system involves the σ * levels of the silyl substituents and the π * orbitals of N,N -dimethylaniline.

The fragmentation characteristics of the trimethyl-Group IV cations have been studied using mass analyzed ion kinetic energy (MIKE), V 1 2 / E (linked) metastable and consecutive reaction monitoring techniques. Both unimolecular (low energy) and collision induced (high energy) decompositions were studied. These methods give information on the ion of interest without interfering contributions from the precursor ion of the trimethyl cation. The results have been interpreted in terms of the decreasing metal—carbon bond strength and the increasing preference for the +2 oxidation state going down Group IV from carbon to lead.

Minimum energy geometries for silirane, 1; 1,1-difluoro-, 1; 1;1-difluorotetramethyl-, 3; 1,1-dimethyl-, 4; hexamethylsilirane, 5; 7-siladispiro[2.0.2.1]heptane, 6; and its 7,7-dimethyl derivative, 7, have been calculated using the CNDO/2 approximation. Good agreement has been obtained between the predicted structure for 7 and an experimental structure for a related compound. The calculations indicate that the enhanced stability observed for the spirocyclopropyl compounds such as 6 or 7 is due for the most part to increased overlap in the σ framework of the silirane ring resulting from increased contributions of the s orbitals of the spiro carbon atoms to the bonding. Hyperconjugation between filled Walsh orbitals of the spirocyclopropyl rings and acceptor orbitals on silicon does not contribute as much to the stabilization of 6 and 7 as does the increased σ overlap. The calculations predict that the 1,1-difluorosiliranes, 2 and 3, should have thermodynamic stability comparable to or greater than the other siliranes, but much higher reactivity due to charge separation.

The regioselectivity of the hydroboration of the methylchlorovinylsilanes, Cl n Me3− n SiCH CH2 ( n = 0 − 3), has been investigated using BH3←THF, 9-BBN, disiamyl- and dicyclohexylborane. Methylation of the adducts with methylmagnesium bromide is complicated by formation of tetraalkylboronates. Alkaline hydrogen peroxide oxidation of the boronates gives reasonable yields of the corresponding α- and β-trimethylsilylethanols for n = 0 and 1. For n = 2 and 3, conversion of the adducts to the corresponding α- and β- deuteroethylsilanes by treatment with excess sodium methoxide in methanol- 0 - d provides a more effective means of derivatization. Addition of the alkenes, n = 2 or 3, to excess BH3←THF gives ca . 90% of the α-boro-organo-chlorosilanes. For all of the alkenes, the dialkylboranes give ca . 80% of the β-boron adducts.

The destructive distillation or pyrolysis of borane 9-borabicyclo[3.3.1]nonane, or dicyclohexylborane adducts to vinylsilanes which have been treated with sodium methoxide in methanol gives significant yields of products resulting from protonolysis of the CB bond. Both α- and β-boro adducts undergo the reaction, which is favored when silicon has methoxy substituents. Quantitative incorporation of deuterium in the saturated products when methanol-O-d is used as the solvent shows that the hydroxyl group of methanol is the proton source. The absence of isomerization of the alkyl groups attached to silicon in the protonolysis of the adducts to propenyltrichlorosilane or isopropenyltrichlorosilane indicates that cyclic intermediates or free carbanions are not involved in the reaction.

The relative stabilities of the cation radicals of several Group IV substituted anilines have been determined by cyclic voltammetry. They are p -tert-butyl- > m -trimethylsilyl- > p -trimethylsilyl- > p -trimethylgermyl- ⪢ N,N -dimethylaniline radical cation. The order of stability parallels that of the compounds towards protodemetalation. CNDO/2 calculations of the charge distribution in the ground states and cation radicals of the molecules resolve the apparent, anomaly in the rates of protodesilylation of m - and p -trimethylsilyl- N,N -dimethylaniline. A mechanism for the chemical reactions of the radical cations which is consistent with the experimental and theoretical results is proposed. It involves nucleophilic displacement of the metal from the cation radical prior to the coupling of the radicals. The relative stabilities of the radical cations of the silicon compounds are in the same order as the amount of π character of the SiC bond in the radical cation. The CNDO/2 calculations indicate that this π character is due to both ( p-p )π and ( p-d )π interactions in the neutral molecules and in the radical cations.

Minimum energy geometries for silacyclopropene, 1,1-difluoro-,1,1-dimethyl,2,3-dimethy1-, and tetramethylsilacyclopropene have been calculated using the CND0/2 approximation. The calculations predict a remarkably small ring CSiC bond angle of about 43.6°. The average ring CC bond length is predicted to be 1.380 A, slightly shorterthan the CC bond length in aromatic rings. Substantial stabilization of the compounds arises from π interaction between the CC double bond and acceptor orbitals on silicon giving significant aromatic character to the molecules.

When E - or Z -1-phenyl-1-methyl-2-neopentylsilene is generated by retro Diels-Alder flash vacuum thermolysis of their corresponding cyclopentadiene or anthracene adducts at temperatures between 400 and 650°C and trapped with 2,3-dimethyl-1,3-butadiene, the stereochemical distribution of the products is independent of the stereochemistry of the silene precursor indicating that the silene is not configurationally stable towards cis-trans isomerization at these temperatures. Evidence that intermolecular “ene” reaction and the [4 + 2] cycloaddition which occur between silenes and the diene are both concerted reactions is presented.

Summary The reaction of t-butyllithium with phenylmethylvinylchlorosilane at low temperature in hexane solvent gave a 48% yield of a mixture of the five isomers of the 1,3-diphenyl-1,3-dimethyl-2,4-dineopentyl-1,3-disilacyclobutanes, along with an acyclic isomer. The separation and determination of the stereochemistry of the diasteromeric 1,3-disilacyclobutanes by means of carbon-13 NMR is described.

Translation diffusion coefficients have been measured for oxyhemoglobin A and oxyhemoglobin S over the concentration range 0.1–37 g/dl by means of photon correlation spectroscopy. The solutions were 0.1 M in KCl and in each case the pH was adjusted to the isoelectric point of the hemoglobin species present. No significant differences were found between the HbA and HbS results; and after correction to water at 20°C, the diffusion coefficients could be described by the equation where Do = (6.93 ± 0.06) × 10−7 cm2/sec and c ids the concentration in units of g/dl. No evidence was found for the aggregation of oxy-HbS at high concentrations which was reported by Lindstrom et. al. [(1976) Biophys. J.16, 679–689].

Le compose du titre cristallise dans le systeme monoclinique, groupe d'espace P21/c et sa structure est affinee jusqu'a R=0,0696

Etude de la pyrolyse du (E)-methyl-2 phenyl-2 neopentyl-3 dibenzo [5,6:7,8] sila-2bicyclo [2.2.2] octane en presence de methoxy trimethyl silane

Determination de la stereochimie relative des diastereoisomeres qui correspondent aux adduits du methanol et des cis et trans phenyl-1 methyl-1 neopentyl-2 trimethylsilyl-2 silaethylenes