Information om | Engelska ordet CARBOCATION

Exempel på hur man kan använda CARBOCATION i en mening

• The reaction involves a carbocation intermediate and is commonly seen in reactions of secondary or tertiary alkyl halides under strongly basic conditions or, under strongly acidic conditions, with secondary or tertiary alcohols.
• In the present-day definition given by the IUPAC, a carbocation is any even-electron cation with significant partial positive charge on a carbon atom.
• The alkyl group may be transferred as an alkyl carbocation, a free radical, a carbanion, or a carbene (or their equivalents).
• Substitution reactions in organic chemistry are classified either as electrophilic or nucleophilic depending upon the reagent involved, whether a reactive intermediate involved in the reaction is a carbocation, a carbanion or a free radical, and whether the substrate is aliphatic or aromatic.
• The benzyl cation or phenylcarbenium ion is the carbocation with formula ; the benzyl anion or phenylmethanide ion is the carbanion with the formula.
• Sometimes however, the stereochemical course is complicated by intimate ion pairs, whereby the leaving anion remains close to the carbocation, effectively shielding it from an attack by the nucleophile.
• This is due to the abstraction of a hydrogen atom by the alkene from the hydrogen halide (HX) to form the most stable carbocation (relative stability: 3°>2°>1°>methyl), as well as generating a halogen anion.
• α-Pinene and β-pinene are both produced from geranyl pyrophosphate, via cyclisation of linaloyl pyrophosphate followed by loss of a proton from the carbocation equivalent.
• Although this reaction appears to be a sulfonation of an unactivated methyl group, the actual mechanism is believed to involve a retro-semipinacol rearrangement, deprotonation next to the tertiary carbocation to form an alkene, sulfonation of the alkene intermediate, and finally, semipinacol rearrangement to re-establish the ketone function.
• For instance in the following alkyl benzenesulfonate the alkene is able to delocalise the carbocation.
• The basicity of triphenylmethanol is enhanced due to the formation of a resonance-stabilized carbocation upon breaking of the C–O bond.
• An alkyl group which is situated trans- to the leaving –OH group may migrate to the carbocation center, but cis- alkyl groups migrate at a very low rate.
• The carbocation is formed by electrophilic addition to the alkene group with electrophiles such as halonium ions, Brønsted acids and Lewis acids.
• Attack of a water molecule on the carbocation and deprotonation is followed by tautomerization to give the α,β-unsaturated carbonyl compound.
• The delocalization of the carbocation reduces the bond order of the polyene chain, thereby reducing the activation energy of the trans-to-cis isomerization.
• The figure to the right depicts photochemical solvolysis of vinyl iodonium salt, through heterolytic carbon-iodine bond cleavage, to generate a vinyl carbocation and iodobenzene.
• In carbocationic polymerization the active site is a carbocation with a counterion in close proximity.
• Containing the tropylium cation and the non-coordinating tetrafluoroborate counteranion, tropylium tetrafluoroborate is a rare example of a readily isolable carbocation.
• Other methods have been proposed in order to promote carbocation formation, including photocatalytic electron transfer or direct photolysis.
• His major scientific contributions include the creation of the first silyl cation (the silicon analogue of the carbocation), elucidation of the mechanism of beta-silyl stabilization of carbocations, discovery of inductive enhancement of solvolytic participation, creation of new methods of conformational analysis by nuclear magnetic resonance spectroscopy (the R value), understanding the conformations of cyclic molecules containing heteroatoms, and development of chemical methods to examine archaeological materials.

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