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High-quality SiOx nanoflowers have been generated by heating mixed SiC/Co powder films in a CO atmosphere. The structural features associated with different stages of the growth were monitored by SEM, TEM, EDX, and XRD analysis. A plausible mechanism for the formation of exquisite flowerlike structures is proposed in which SiC reacts with CO, the Co particles acting as a catalytic template, to yield amorphous SiOx branches. Numerous loops and branches were also observed which may arise either as a result of bifurcation or coalescence. Use of Co2O3 instead of Co as catalyst leads to abnormal flowers exhibiting secondary growth.

Novel W–Nb–S composite inorganic nanotubes have been generated by replacing W in the S–W–S sandwich layers of WS2 by Nb. The tubes are uniform, with the Nb concentration 10 atom%. Raman spectral features of the tubes are described.

In this paper, a systematic study of large-scale production of highly crystalline W18O49 nanoneedles with high aspect ratios using a simple tungsten metal reacting with water at 800−1000 °C has been described. By altering the W source and other experimental conditions, we have generated W18O49 crystals with diverse morphologies, and needles with desired dimensions are achieved. The quality nanoneedles provide ideal samples for further property investigations. Possible growth mechanisms are discussed.

Novel ceramic and carbon nanostructures have been created by thermolysis of mixtures containing polytetrafluoroethene (PTFE) and a pure metal or metal alloy in a calorimetric bomb. The influence of the stoichiometry was studied for Si-containing reactants for which the yield of the nanofibers was the highest. The process was monitored by measuring the heat of reaction and by differential thermal analysis/thermogravimetric techniques. The reaction temperatures were measured, and the heating rates of the reactants during thermal wave propagation were estimated. Elemental analysis, X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and energy dispersive X-ray spectrometry were employed to characterize the chemical composition and structural features of the products. Well-crystallized elongated single-crystal Si nanofibers, coated with a thin SiO2 amorphous layer, and crystallized carbon nanoparticles containing metals (e.g., Fe) and Si dominate. The highest yie...

The oxidation of polystyrene, polyethylene, polypropylene and poly(vinylidene fluoride) is retarded by carbon nanotubes. Incorporation of boron into the nanotubes enhances the electron affinity of the tubes and leads to a small increase in antioxidant efficiency.

Novel binary-phase WS2−C nanotubes were generated by pyrolyzing WO3-coated multiwalled carbon nanotubes in an H2S/N2 atmosphere at 900 °C. The WS2 coating acts as an anti-oxidizing agent.

Using a simplified in-situ process, we have successfully generated relatively long IF WS2 nanotubes, in good yield and purity. The nanotubes are formed directly from WOx nanorods created from W and SiO2 during the first stage. Structural similarities and differences between IF nanotubes and carbon nanotubes have been analyzed. A noteworthy feature of the WS2 tubes is that some of their tips are fully open.

Recently, we have shown that [60] fullerene (C 60 ) may be produced by pyrolysis of the bowl-shaped corannulene molecule under a wide range of conditions. Both naphthalene and its dimer benzo [ k ] fluoranthene may be employed as precursors to C 60 .

Previous work on polyhydrogenation of fullerenes leading to C 60 H 36 and C 70 H 36 as the main products is reviewed. The most probable structures of these species, based on their aromaticities, are presented. Zinc/concentrated HCl is shown to be an excellent and rapid reducing agent for benzene or toluene solutions of fullerenes at room temperature. The polyhydrogenated species are unstable towards light and undergo oxidative degradation, with, in the case of C 60 H 36 , formation of C 60 H 18 as an intermediate. Reduction of these fullerenes by zinc/concentrated DCl gives C 60 H 44 and C 70 H 48 as the highest hydrogenated products; the greater incorporation of deuterium is attributed to the greater C-D bond energy. In the absence of light and oxygen, C 60 H 36 exhibits high thermal stability. Attempted further reduction of C 60 H 36 leads to formation of trimethylene adducts; these are also formed on reduction of [84] fullerenes which gives C 84 H 48 as the main product.

Block polymers of methyl methacrylate and methacrylic acid have been prepared using the technique of enolate-initiated anionic polymerisation, employing trimethylsilyl methacrylate as a precursor for the methacrylic acid component. The structure of the product has been characterised by infra-red and NMR spectroscopy, and by thermogravimetric analysis.

Aligned carbon nanofibers/tubes, ca. 20-50 nm in diameter, were generated by hollow cathode glow discharge decomposition of Fe(C 5 H 5 ) 2 in He at ca. 200 °C on an Al 2 O 3 membrane. The as-deposited product consists of bundles of amorphous carbon nanofibers with numerous Fe nanoparticles embedded therein. Heating at 1100 °C under Ar produced well-crystallized carbon nanotubes.

La conformation est etudiee en utilisant 3 couples accepteur/donneur differents par leur distance critique de transfert d'energie; les resultats sont compares a des resultats precedents. A degre d'ionisation faible, le polymere adopte une conformation tres peu allongee. A haut degre d'ionisation, la structure est en zigzag. Les distances bout-a-bout obtenues avec cette technique sont des distances «reelles» entre 2 groupes terminaux reactifs qui subissent une reaction sur une duree d'une nanoseconde; elles sont beaucoup plus faibles que celles des chaines non perturbees

La validite de la methode precedemment proposee est demontree en l'appliquant au cas d'un poly(methacrylate de methyle) portant des groupes terminaux chromophores etudie dans differents solvants. La principale source d'erreur provient de l'incertitude des mesures viscosimetriques de la distance bout-a-bout quadratique moyenne du polymere

Mesure de l'efficacite du transfert d'energie entre les groupes accepteur et donneur attaches aux extremites de chaines de PMMA et calcul a l'aide des equations developpees precedemment des distances bout a bout efficaces. Comparaison des valeurs obtenues dans des solvants non visqueux et dans une matrice solide de PMMA avec les valeurs obtenues par viscosimetrie

A new class of ioneneomeric polymer liquid crystals made by double quaternization of the trans-1,2-bis(4-pyridyl)ethene unit with an appropriate spacer, X(CH2)nX (where n = 4–10, 12; X = MeSO3 or 4-MeC6H4SO3), has been prepared. Mesophase transition temperatures and stabilities are independent of the anion and length of spacer. Differential scanning calorimetry, polarizing optical microscopy and X-ray studies reveal that these polymers exhibit disclination or extinction-band texture.

An in situ polycondensation approach was applied to functionalize multiwalled carbon nanotubes (MWNTs), resulting in various linear or hyperbranched polycondensed polymers [e.g., polyureas, polyurethanes, and poly(urea-urethane)-bonded carbon nanotubes]. The quantity of the grafted polymer can be easily controlled by the feed ratio of monomers. As a typical example, the polyurea-functionalized MWNTs were measured and characterized in detail. The oxidized MWNTs (MWNT-COOH) were converted into acyl chloride-functionalized MWNTs (MWNT-COCl) by reaction with neat thionyl chloride (SOCl2). MWNT-COCl was reacted with excess 1,6-diaminohexane, affording amino-functionalized MWNTs (MWNT-NH2). In the presence of MWNT-NH2, the polyurea was covalently coated onto the surfaces of the nanotube by in situ polycondensation of diisocyanate [e.g., 4,4'-methylenebis(phenylisocyanate)] and 1,6-diaminohexane, followed by the removal of free polymer via repeated filtering and solvent washing. The coated polyurea content can be controlled to some extent by adjusting the feed ratio of the isocyanato and amino groups. The structure and morphology of the resulting nanocomposites were characterized by FTIR, NMR, Raman, confocal Raman, TEM, EDS, and SEM measurements. The polyurea-coated MWNTs showed interesting self-assembled flat- or flowerlike morphologies in the solid state. The signals corresponding to that of the D and G bands of the carbon nanotubes were strongly attenuated after polyurea was chemically tethered to the MWNT surfaces. Comparative experiments showed that the grafted polymer species and structures have a strong effect on the Raman signals of polymer-functionalized MWNTs.

Formation of rounded forms of carbon offers a unique opportunity to study the properties of materials constrained in nanoscale environments. Encapsulation of molybdenum carbide in polyhedral carbon nanoparticles is found to stabilize the face-centered-cubic form at the expense of the commonly encountered hexagonal-close-packed form. This reveals an important role for the carbon nanoclusters and/or nanotubes of catalyzing the synthesis of materials with novel structural forms in their nanoscale environment. The encapsulated carbide is superconducting with a Tc ∼ 10.5 K.

When nanotubes form in a carbon arc, the presence of boron results in long boron-doped carbon nanotubes which are generated as dominant zigzags. Metallic behaviour is observed, in contrast to carbon nanotubes, which are semi-conducting.

The geometry and electronic structure of three C60 derivatives (C60Cl6, C60Ph5Cl and C60Ph5H) are studied by means of spectroscopic measurements in cyclohexane solution and semi-empirical Hartree-Fock quantum-chemical calculations. A good agreement between observed and simulated spectra is reported. Based on the latter, the importance of symmetry and nature of the functional groups on the properties of the C60 cages is discussed.

Novel flower-like nanostructures consisting of silicon oxide nanofibers, radially attached to a single catalytic particle, were generated by solid-solid and gas-solid reactions under a temperature gradient. In this process, a mixture of SiC and Co powders, deposited on silica substrates and heated under an Ar/CO atmosphere at ca. 1500C, produced material with unusual three-dimensional (3D) networks of nanofibers of uniform diameter (ca. 20-120nm) and length (ca. 10-250mu;m). Scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray powder diffraction and energy dispersive X-ray (EDX) analyses reveal that the nanofibres are amorphous and consist only of silicon oxide, generated from the reaction of CO with SiC. Nanostructure formation is catalyzed by Co particles, which act as nucleation sites and templates for 3D growth. Experiments using Si3N4 and Si in conjunction with other catalysts (e.g. Fe, Ni and CoO) yield similar results and confirm that the resulting SiOx fibres display virtually unique and remarkable radial growth starting from single metal particles. These structures exhibit morphologies comparable to radiolarian and diatom skeletons and may provide insight into the formation of microbiological systems.

NbS2 nanotubes/rods have been generated successfully employing carbon nanotube template promoted growth; high resolution transmission electron microscopy, coupled with EDX analysis, confirm the template effect and existence of NbS2 tube structures.

[60]Fullerene derivatives, C60Ar5Cl (Ar = Ph or 4-FC6H4), react with AlCl3 in solution at room temperature to form Cs symmetrical pentaaryl[60]fullerene carbocations, C60(Ar)5+.

Reaction of C60Ph5Cl with cyanogen bromide results in replacement of the chlorine by BrCN and ring closure between the addend and an adjacent phenyl ring, giving a 1-bromoisoquinoline derivative of [60]fullerene; this readily undergoes nucleophilic replacement of Br by OH to give the corresponding 1-isoquinolone derivative.

In the presence of phosphine catalysts, ethyl buta-2,3-dienoate and ethyl but-2-ynoate undergo [3 + 2] as opposed to [2 + 2] dipolar cycloaddition to [60]fullerene.

On exposure to air, both C 60 Ph 5 H and C 60 Ph 5 Cl spontaneously oxidise with elimination of the hydrogen or chlorine attached to the cage and the ortho hydrogen of the adjacent phenyl group, giving a benzo[b]furanyl[60]fullerene; a second oxygen is located in the pentagon that is surrounded by phenyl groups.

Metal particle-catalysed generation of a series of novel nanostructures, via the well-known VLS step first described as a micrometer-scale fibre growth mechanism, is discussed. The resulting nanomaterials were characterised using HRTEM, SEM, EDX and XRD, and the results showed that these materials could be valuable components in constructing nano- and micro-machines.

The cleavages of cis- and trans-PhCHCHSnMe3 in 1/10 AcOD-MeOD have been shown to give cis- and trans-PhCHCHD, respectively. The rates of cleavage of some XC6H4CHCHSnMe3 compounds in 1/10 AcOH-MeOH at 50°C have been measured; there is no significant difference between the rates for cis- and trans-PhCHCHSnMe3, and the relative rates of cleavage as X is varied are (X  H), 1.0; p-OMe, 7.0; p-Me, 2.3; m-Cl, 0.34; m-Br, 0.36. There is an excellent correlation with σ+ constants, with a ρ value of 1.1. The results are interpreted in terms of rate-determining proton transfer to the β-carbon atoms, and it is suggested that acid cleavages of vinylHgX bonds involve analogous mechanisms. PhSnMe3 is cleaved 20 times as slowly as PhCHCHSnMe3 in the 1/10 AcOH/MeOH. The rates of cleavage of XC6H4CHCHSnMe3 compounds by a mixture of MeOH (3 vol.) and 2 M aqueous NaOH (2 vol.) have been measured; trans-PhCHCHSnMe3 is cleaved about 1.3 times as rapidly as its cis-isomer, and about 12 times as rapidly as a mixture of cis- and trans-PhCHCHSnEt3. The relative rates for the various XC6H4CHCHSnMe3 compounds (mainly trans-isomers) are (X ) H, 1.0; p-OMe, 0.99; p-Me, 0.92; m-Cl, 1.67; m-Br, 1.65. Cleavage of trans-PhCHCHSnMe3 by NaOD/D2O/MeOD gives exclusively trans-PhCHCHD. For cleavages in methanolic NaOMe the values of the rate isotope effects, (the ratio kmeOH/kMeOD) are 2.3–2.6, and those of the product isotope effects, PIE (the product ratio RH/RD on cleavage of RSnMe3 by NaOMe in 1 : 1 MeOH/MeOD) are 4.5–5.0. The results are interpreted in terms of proton transfer from the solvent to the leaving carbon atom in the rate determining step as the SnC bond breaks as a result of the attack of the base anion at tin in a prior or synchronous process. PhCHCHSnMe3 is cleaved by the aqueous alcoholic base about 5 times as rapidly as PhSnMe3. Cleavage of trans-PhCHCHSnMe3 by PHCOCl in presence of AlCl3 in CH2Cl2 gives trans-PhCHCHCOPh, and cleavage of a 90/10 mixture of trans- and cis-PhCHCHSnMe3 by bromine in CCl4 gives a corresponding mixture of trans- and cis-PhCHCHBr.

The electronic effects of the silatrane group have been studied by examination of the 19F NMR spectra of 1-(m- and 1-(p-FC6H4CH2)silatrane and the charge transfer spectra of the TCNE complexes of 1-phenyl- and 1-benzyl- silatrane. Along with a quite large electron-releasing inductive effect, the CH2silatrane group has a substantial electron-releasing hyperconjugative effect, though this is somewhat smaller than that of the CH2SiMe3 group.

Lithium alkynethiolates, RCCSLi, react rapidly with trialkylmetal (IVB) halides, R 1 3 MX, to give the novel metal-substituted alkynethiols, RCCSMR 1 3 .

Treatment of (Me 3 Si) 3 CLi (“trisyl”lithium, TsiLi) with appropriate silicon halides has given a range of compounds of the type (Me 3 Si) 3 CSiRR′X; e.g., TsiSiCl 3 , TsiSiMeCl 2 , TsiSiMe 2 X (X = Cl, OMe), TsiSiPh 2 X (X = F, Cl, OMe), and TsiSiPhMeH. The trisyl group causes very large steric hindrance to nucleophilic displacements at the silicon to which it is attached, so that (unless one or more hydride ligands are present) most of the common displacements at silicon do not occur. However, halides can be reduced to hydrides by LiAlH 4 , and the hydrides can be converted into halides in electrophilic displacements by hallogens. The presence of even one hydride ligand markedly reduces the hindrance, so that, for example, TsiSiPhHI reacts with refluxing methanol to give TsiSiPhH(OMe).

Rates of cleavage in sulphuric acid/acetic acid mixtures at 50° have been measured for (2-methoxy-5-nitrophenyl)-, (2-methoxy-5-carboxyphenyl)-, (4-methyl-3-nitrophenyl)- and (2-methoxy-5-acetylphenyl)trimethylsilane. In the case of the first two compounds the reactivities are much as expected for additivity of the separate effects of the activating and deactivating substituents, but the 4-methyl-3-nitrophenyl compound is a little less reactive than expected, possibly because of some steric interaction between the adjacent methyl and nitro groups. The reactivity of the 2-methoxy-5-acetylphenyl compound indicates that the deactivating effect of an acetyl group on the meta-position is similar to that of a carboxy group.

Rates of uncatalysed cleavage of the compounds (XC6H4)Me2SiNMePh where X = H, p-OMe, p-Me, m-Me, m-Cl, or p-Cl, have been measured for solvolysis by solutions of sodium acetate in ethanol. Electron release by X increases the rate of the reaction, and there is an excellent correlation with the σ-constants of the X groups ( ϱ = −0.96). The mechanism is discussed in the light of this.

p-TolylC≡CPh is converted efficiently into PhC≡CPh and p-tolylC≡Ctolyl-p (metathesis) by [Mo(CO)3(PhOH)] in n-octane at the reflux temperature. Other molybdenum complexes, e.g. [Mo(CO)3(NH3)3], [Mo(CO)3(MeCN)3], trans-[Mo(CO)4(PPh3)2] and cis-[Mo(CO)2(Ph2PCH2PPh2)2] also catalyse metathesis, the first two in the absence of phenol. Coordinatively unsaturated species such as “Mo(CO)3” are considered to be active in promoting metathesis, the role of phenol being to provide an unstable intermediate complex, rather than to assist in removal of complexed acetylene from molybdenum as envisaged hitherto.

A kinetic study has been made of the reaction of some 1-organosilatranes with aqueous-methanolic hydrochloric acid. The reaction is of first-order in both silatrane and acid, and for XC6H4,-silatranes electron release by X assists the reaction. For acid catalysis in water or in water/dioxan, the rate is effectively the same irrespective of whether protium oxide or deuterium oxide is used. It is suggested that the rate-determining step involves protonation of the nitrogen atom concerted with breaking of the SiN bond, the protonation being almost complete at the transition state.

Phenyl azide and ethyl diazoacetate add ‘ endo ’ to Me 3 Si(CC) 2 SiMe 3 . 4-Nitrophenyl azide reacts exclusively with the triple bond adjacent to silicon in Me 3 Si(CC) 3 SiMe 3 , also in the ‘ endo ’. The regio- and site-specificity exhibited in these cycloadditions is attributed to orbital rather than to steric control.

Rates of cleavage by aqueous methanolic alkali have been measured for the CMR 3 bonds in some arenechromium tricarbonyl complexes. The complex ( h 6 -PhCCGeEt 3 )Cr(CO) 3 is 16 times as reactive as the uncomplexed PhCCGeEt 3 towards a mixture of methanol (5 vol) and aqueous alkali (1 vol) at 30°, which leads to a value of +0.84 for the σ-constant of the Cr(CO) 3 group. The relative rates for the complexes ( h 6 -XC 6 H 4 CCGeEt 3 )-Cr(CO) 3 with varying X correlate excellently with those for the uncomplexed XC 6 H 4 CCGeEt 3 compounds, showing that the Cr(CO) 3 group causes no distortion of the pattern of substituent effects, but the groups X have a smaller influence on the rate in the complexed series. The arylSiMe 3 bond of the complex ( h 6 -PhSiMe 3 )Cr(CO) 3 is much more readily cleaved by base than that in the uncomplexed PhSiMe 3 , but the pattern of substituent effects in ( h 6 -XC 6 H 4 SiMe 3 )Cr(CO) 3 complexes is consistent with that in the series XC 6 H 4 SiMe 3 . The complex ( h 6 -PhCH 2 SiMe 3 )Cr(CO) 3 is some 3 × 10 5 times as reactive as PhCH 2 SiMe 3 towards methanol (5 vol) containing aqueous alkali (1 vol) at 30°, which corresponds to an approximate value of +1.12 for the σ − -constant of the Cr(CO) 3 group.

Organolithium reagents prepared from BrC6H4SMR3 compounds (R3M = Me3Si,Et3Si, PhMe2Si, Me3Ge) and butyllithium rearrange rapidly in ether solution to R3MC6H4SLi species, which upon treatment with water yield benzene thiols R3MC6H4SH. Under Wurtz—Fittig “in situ” conditions the organosodium intermediate NaC6H4SSiMe3 does not rearrange but couples normally with Et3SiBr to give Et3SiC6H4SSiMe3, which on methanolysis gives Et3SiC6H4SH. These reactions provide useful new routes to silyl- and germly-substituted benzene thiols.

We have measured spectrophotometrically the rates of cleavage by aqueous methanolic alkali of some (XC 6 H 4 ) 3 SiCCPh compounds, and also of some YC 6 H 4 CCMR 3 compounds in which M  Si or Ge. (Phenylethynyl)trimethylsilane undergoes cleavage ca. 10 7 times as fast as benzyltrimethylsilane. Reaction is facilitated by electron-withdrawal and retarded by electron-release in the subtituents X or Y. The effects of the substituents Y, but not of the substituents X, can be correlated approximately with their Hammett σ-constants. Solvation of the forming carbanion YC 6 H 4 CC − is thought to be of considerable importance, and steric hindrance to such solvation (which is smaller for GeR 3 than for SiR 3 compounds) may be the major cause of the following effects: ( a ) The (phenylethynyl)-SiMe 3 bond is broken by alkali much less readily than the (phenylethynyl)-H bond, ( b ) the silicon compound PhCCSiMe 3 is only 34 times as reactive as the corresponding germanium compound PhCCGeMe 3 , ( c ) the trimethylcompound PhCCSiMe 3 is 280 times as reactive as the corresponding triethyl compound, which is ca. 1350 times as reactive as the corresponding triisopropyl compound.

The 19 F NMR spectra of m - and p -[(Me 3 Si) x CH (3-x) ]C 6 H 4 F (x = 0-3) compounds have been recorded. The σ 1 and σ U R constants for the (Me 3 Si) x CH (3-x) groups which can be derived from the 19 F chemical shifts are of doubtful validity, and the results suggest this method of obtaining σ 1 and σ U R constants may not be applicable to substituents of this type.

Infrared intensities are recorded for the η 8 ring-stretching band near 1600 cm −1 of a series of meta - and para -substituted ArCH 2 SiMe 3 and ArCH 2 SnMe 3 compounds. The substituents CH 2 SiMe 3 and CH 2 SnMe 3 are confirmed as resonance donors, with σ O R of −0.20 and −0.26 respectively.

Bis(trimethylsilyl)acetylenes, Me 3 Si(CC) n SiMe 3 , react with acyl chloride-aluminium chloride complexes, XC 6 H 4 COCl·AlCl 3 in methylene chloride at 0–20° to form the corresponding ketones XC 6 H 4 CO(CC) n SiMe 3 in excellent ( n = 1) or moderate ( n = 2, 4) yield. Treatment of the products with aqueous methanolic borax results in virtually quantitative liberation of the terminal alkynyl ketones XC 6 H 4 CO(CC) n H. The method provides the first practical route to the ketotetraynes ( n = 4) and usefully supplements existing oxidative methods for keto-monoyne and -diyne synthesis. The oxalyl chloride-aluminium chloride complex reacts with Me 3 SiCCSiMe 3 to give the novel silyl-substituted heterocycle (I)

The rates of cleavage of the 1-, 3-, and 4-trimethylsilyl derivatives of 1,2-dihydrobenzocyclobutene (“benzocyclobutene”) (I) by potassium hydroxide in dimethyl sulphoxide—water have been measured spectrophotometrically. The 3-derivative is 10.6 times as reactive as its 4-isomer, and 8.5 times as reactive as its closest analogue 1,2-dimethyl-3-trimethylsilylbenzene. The results are consistent with enhanced electronegativity of the 3-carbon atom [and thus enhanced acidity of the 3-position of (I)], which is associated with the effect of the ring-strain on the hybridization of the orbitals of the atoms of the 4-membered ring. The reactivity of the 1-derivative is much greater than that of its 3- and 4-isomers, and rather similar to that of its analogue, α-(trimethylsilyl)ethylbenzene; any enhancement of the electronegativity of the 1-carbon atom appears to be balanced out by the less effective delocalization of a lone-pair from the 1-carbon into the aromatic ring. In the strongly-basic medium used (0.05 M KOH in dimethyl sulphoxide containing 3 wt. % of water), phenyltrimethylsilane is some 9 times as reactive as its tin analogue; this unusual order of reactivity may be associated with a smaller contribution from proton-transfer to the separating carbon atom in a medium of low hydroxylic content.

When solvolysis of the bromide Me3SiCH2CD2Br by aqueous methanol is allowed to proceed to about 50% completion, the recovered bromide contains Me3SiCD2CH2Br and Me3SiCH2CD2Br, in 1 2 ratio. This migration of the Me3Si group is consistent with a mechanism involving anchimerically assisted ionization of the CBr bond to give a silacyclopropenium ion.

The compounds m - and p -(Me 2 CCH 2 )C 6 H 4 SiMe 3 have been synthesized, and the rates of their cleavage by aqueous-methanolic perchloric acid have been measured and compared with those of the corresponding m - and p -(Me 3 SiCH 2 )C 6 H 4 SiMe 3 compounds. The results show that the inductive release of electrons to a saturated carbon atom is markedly greater for the Me 3 Si than for the Me 3 C group.

The scope of the hydrosilylation of olefins catalysed by tert-butyl peroxide under UV irradiation has been studied briefly. Some conclusions are as follows: (i) The reaction between trichlorosilane and 1-hexene is not affected by temperatured change in the range -20 to +40°; (ii) good yields of trichlorosilane adduct can be obtained from trichlorosilane and 1-hexene, 1-octene and cyclohexene, but yields are very poor with 2-octene and 2-methyl-2-butene; (iii) dichloro(methyl)silane gives, acceptable yields though markedly lower than those from trichlorosilane, but triethysilane, triethoxysilane, triphenylsilane and 1,1,1,3,5,5,5-heptamethyltrisiloxane do not give detectable yields of adducts under the conditions used. Trichlorosilane has been found to react with benzene under similar conditions to give phenyltrichlorosilane in 16% yield.

The apparent dissociation constants of the acids p-[(Me3Si)xCH(3−x)]C6H4CO2H in 50% aqueous ethanol at 25° have been measured and used to give the following σ-constants for the p-[(Me3Si)xCH(3−x)] groups: x = 1, −0.29; x = 2, −0.33; x = 3, −0.27. The rates of solvolysis of the tertiary chlorides p-[(Me3Si)xCH(3−x)]C6H4CMe2Cl in aqueous acetone have also been measured and used to give the following σ+-constants: x = 1, −0.54; x = 2, −0.62; x = 3, −0.52. The results are consistent with the existence of substantial hyperconjugative electron release from the Me3SiC bonds.

The ESR spectra of the radical anions of o-, m-, and p-(trimethylsilyl)- and p-(triethylgermyl)nitrobenzene have been measured in methanol solutions. The 14N isotropic hyperfine interactions are discussed in terms of the substituent effects of the organometallic groups. Satellite spectra from 29Si and 73Ge have also been observed.

The rates of cleavage of alkynyl-silicon bonds in (a) Et 3 Si(CC) n SiEt 3 , (b) Et 3 Si(CC) n H, and (c) Mesityl(C) n SiEt 3 compounds at 29.6° in aqueous methanol containing alkali or a base buffer have been measured in order to assess both the attenuation of hydrocarbon acidity and the maximum electron-withdrawing effect attained by long-chain conjugated terminal polyyne systems. The results, expressed as relative rates within each of the series, are as follows: (a) ( n , rel. rate) 2, 1.0; 3, 17.4; 4, 86.8; 6, 357; 8, 570; 9, 575. (b) 1, 1.0; 2, 98; 3, 1790; 4, 8017; 6, 27450; 8, 42530. (c) 2, 1.0; 3, 40; 4, 220; 5, 760. In so far as the systems studied are representative, the figures indicate that both the acidity of the parent polyynes, H(C) n H, and the electron-withdrawal by H(CC) n groups attenuate rapidly as n increases, reaching limiting values for n = 8−10.

An infrared method has been used to establish that the SiMe 3 group is a weak resonance acceptor in the ground state when joined to a benzene ring. This acceptance is considerably exalted when resonance donors are attached to the para position. The relatively strong resonance donation of a CH 2 SiMe 3 group is explicable in terms of hyperconjugation.