Showing papers on "Bond cleavage published in 1969"

Some recent studies of the cleavage of carbon-silicon and related bonds

Abstract: This brief review will be concerned with heterolytic cleavages of carbon— silicon and related bonds, and will concentrate on some more recent investigations by the author and his co-workers. The C—Si bond is fairly stable towards homolytic fission, and under free radical conditions the C—H bonds of organosilicon compounds are usually more readily attacked than the C—Si bonds1. The C—Si bond is moderately polar, however, (Pauling electronegativities indicate that there is 12% ionic character in the direction CSi+), and is relatively easily attacked by ionic reagents. Since C—H bonds break heterolytically in the same direction, C-Hf, a good indication of the behaviour of an R—Si bond can be obtained by considering the reactions of the corresponding R—H bond2. For example, just as the C—H bond of chloroform, HCC13, is readily broken by attack of hydroxide ion on the hydrogen atom, so the Si—C bond of the compound Me3SiCC13 is broken, even more readily, in alkali, by nucleophilic attack at silicon. Again, just as aryl—H bonds are broken readily by electrophilic reagents such as bromine or sulphur trioxide, so aryl—SiMe3 bonds are also broken readily by these reagents. It is usually but not always true that an R—SiMe3 bond is more reactive than the corresponding R—H bond towards ionic reagents.

The Reactivity-Hydrolysis Relationship in Chemical Finishing of Cotton1

Abstract: The reactivity-hydrolysis relationship in chemical finishing of cotton with N-methyloltype reactants under acidic conditions has been discussed. Theoretical and practical justifications for the relationship have been presented to demonstrate that the ease of formation of links is related directly to the ease of hydrolysis of links, and relative rates in both directions are predictable, based on steric and electronic effects on the resonance-stabilized intermediate. Bond cleavage during hydrolysis has been shown to occur first at the carbon-oxygen bond of the methylol groups, whether or not the link was formed from a substituted urea-formaldehyde adduct or a substituted urea-glyoxal adduct. Limitations for the relationship are also discussed.

Photolysis of phenacylsulphonium salts

Abstract: Dimethylphenacylsulphonium bromide undergoes photolysis with homolytic cleavage of the C–S bond.

Synthesis of enol sulphonates from carbonyl compounds

Abstract: Sulphonic anhydrides and dimethylformamide convert ketones and aldehydes into enol sulphonates, which are generally relatively stable towards acids and bases but regenerate the carbonyl compounds by O–S bond cleavage on more vigorous treatment.

LCAO-MO-SCF Studies of Carbon-Carbon Bond Cleavage in Ethylene Oxide

Abstract: Nonempirical LCAO–MO–SCF studies of carbon–carbon bond cleavage in ethylene oxide indicate the presence of two open forms. In one form (the 90, 90 form) the terminal methylene groups are perpendicular to the C–O–C plane. In the other (the 0, 0 form), the terminal methylene groups are in the C–O–C plane. On the basis of molecular correlation diagrams such as those of Hoffmann and Woodward, one would expect that either of these open forms could add stereospecifically to olefins. Previously Huisgen had suggested that the 0, 0 open form was an intermediate in the 1, 2 cycloaddition of tetracyanoethylene oxide to olefins; however, a 90, 90 form is also consistent with the experimental data.

Electron impact studies. XLVIII. Specific hydrogen-rearrangements in the mass spectra of ortho-alkoxyanils

Abstract: The mass spectra of anils with ortho-alkoxyl substituents in the aromatic ring derived from the aldehyde contain pronounced peaks prod- uced by C=N bond cleavage accompanied by one and/or two hydrogen transfers to the nitrogen-containing fragment. Deuterium-labelling studies show that the hydrogen atoms involved are those attached to the α-carbon (α to oxygen) of the alkoxyl group. The extent of the hydrogen rearrangements may be altered by the addition of further substituents to the aromatic rings.

Kinetics of the Reaction of Benzyl Bromides with Thiourea

Abstract: The kinetics of the reaction of m-or p-substituted benzyl bromides with thiourea in methanol at 35.0were determined by an electric conductivity method. According to a plot of log k against the Hammett substituent constants, C-Br bond cleavage in benzyl bromide is postulated to be a rate determining step at the SN2 reaction of benzyl bromide with thiourea. Both electron-donating substituents and electron-withdrawing substituents quantitatively affected the rate of reaction, but each in a different manner. A mechanistic possibility was proposed to account for the results. Some activation parameters were also calculated.

A novel pyrolytic rearrangement of trans-1,3-dibenzoyl-2-phenylaziridine

Abstract: trans-1,3-Dibenzoyl-2-phenylaziridine undergoes thermal rearrangement to 1,4-diphenyl-4-benzoyloxy-2-azabutadiene via carbon–carbon bond cleavage of the aziridine ring.

Tri‐o‐tolylphosphine: A rapid photopolymerization initiator

Abstract: The rate of tri-o-tolyphosphine-initiated photopolymerization of methyl methacrylate was found to be significantly higher than that for the triphenylphosphine initiated polymerization. The mechanism was shown to be dependent upon the concentration of the initiator. At low concentrations (10−4 mole/l.), an activated complex is the initiating species, while at higher concentrations (above 10−2 mole/l.) homolytic cleavage of the phosphorus–carbon bond is the radical source. Steric inhibition of resonance is advanced as an explanation for the enhanced activity of tri-o-tolylphosphine over triphenylphosphine.

Application of Molecular Orbital Theory to the Bond Scission of Amino Acid Esters

Abstract: 計10種のアミノ酸エステルの電子衝撃による骨格結合の一次切断確率をMO理論的に算出すると,質量スペクトルからの実測値と満足すべき一致を示す。その計算に用いた各官能基に関するパラメーターはケトン,アミン,エステル,アルコール,チオールなどで最適とされたものである。しかもその一致は理論の要求するように低電位衝撃の方が良好である。これらの結果は官能基に特有なパラメーターの転用可能性を示す。したがって,前報の結果と合わせ考えると,本理論が少なくとも経験的方法としてアミノ酸エステルのみならず,各種の鎖状飽和化合物の質量スペクトルの予言と解釈に有用なことを示すといえよう。メチオニンに関するSvecの説明は衝撃電位の変化に基づき基準ピークが変わるので,必ずしも妥当でないことを実験的に明らかにし,これを本理論では説明できることを示した。