Alkylhalides: Substitution reactions 4 (Sn1)

Alkylhalides: Substitution

Nucleophile substitution reaction (Sn1 reaction)

To kick off this new chapter from the alkylhalides, some experimental background theory concerning Sn1 reactions:

the reaction rate of the reaction depends ONLY on the concentration of the alkyl halide (unlike Sn2 reactions where the nucleophile concentration was important aswell !!!).
the reaction rate of the reaction INCREASES if the alkylhalide is more branched at its reaction center (again unlike Sn2 reactions where more branched reaction centers are LESS active !!!). This means a tertiary alkyl bromide f.e. will have a huge relative reaction rate, methylbromide on the other hand will have no Sn1 reaction.
when an alkyl halide reacts with its enantiomere (cfr. stereochemistry), the reaction product will be a racemic mixture (this is a mixture of two enantiomeres of the same compound) or partial racemic product.

Conclusion: this indicates at the presence of a CARBOCATION intermediate

The Sn1 reaction is a two step reaction. The leaving group has already left the alkylhalide before the nucleophile comes in to play. See the example for more details:

Reaction rate Sn1 reaction

The reaction rate of the Sn1 reaction is dependent on the following basic rules:

the better the leaving group the faster the reaction will take place and be finished.
if the carbocation is very very stable, the reaction rate will be high.
the more polar the solvent is, the higher the reaction rate.

as stated before, the concentration of the attacking nucleophile has effect at all on the Sn1 reaction. Why? It is not implemented in the rate-determing step.

Comments

Alkynen: Elektrofiele additie

Elektrofiele additie: Waterstofhaliden op alkynen Voorbeeld van waterstofhaliden: HCl, HBr, HF, HI Gebruik van één equivalent waterstofhalide met alkyn (dus 1:1 geen overmaat geen tekort) Bij een overmaat aan het waterstofhalide zal een tweede reactie plaatsvinden op het gehalogeneerde alkyn, ter vorming van een geminaal regioisomeer.

Alkanes and radicals 4: Additionreactions of radicals

Alkanes and radicals Addition of radicals on an alkene Look at the two reactions below, the first reaction is in normal circumstances, which will result in a normal Markovnikov reaction ( with the addition of a protic acid HX to an alkene , the acid hydrogen (H) becomes attached to the carbon with fewer alkyl substituents , and the halide (X) group becomes attached to the carbon with more alkyl substituents). In the second reaction, peroxide is used as condition, this will result in an anti-Markovnikov reaction. The peroxide will generate Br radicals in small amounts (this is the initiation for this anti-reaction). Let's see the peroxide mechanism in detail. As stated above, an alkyl peroxide is a radical initiator. The electrophile will add on the sp2 carbon which carries the most hydrogens (where also the radical with most alkyl groups will be formed). The termination reactions will have several other outcomes. In the major outcome, the radical will not b

Meadowsweet under the microscope - 1

We acquired some meadowsweet powder and put it under a microscope, following the standard procedure of the European Pharmacopeia (using some droplets of a chloralhydrate solution (80 g in 20 mL)), heating followed by cooling, to minimize the crystallization process of chloralhydrate. Namely a phase contrast microscope. What we saw was a lot of irrecognisable structures, cells, celldebris, trichoma's (hairs), stoma, ..., but fascinating nonetheless.

Pharmacist Blog about what I encounter and find useful/interesting

Search This Blog