Skip to main content

Alkylhalides: Substitution reactions 6 (Sn1)


Alkylhalides: Substitution

Nucleophile substitution reaction (Sn1 reaction)
Sn1 side reactions
I will now discuss some side reactions that can occur when a Sn1 reaction takes place.


Carbocation shift
Illustrated in the scheme below:


Benzyl- and allylhalides 
Benzyl- and allylhalides can undergo Sn1 AND Sn2 reactions. How to distinct them?

  • Sn1 conditions: protic solvent and by adding a weak attacking nucleophile. Note: Benzyl- and allylhalides easily undergo Sn1 reactions, because their carbocations are very stable.
  • Sn2 conditions: aprotic solvent and by adding a strong attacking nucleophile. Note: tertiary benzylhalides and tertiary allylhalides will NOT undergo a Sn2 reaction because of the steric effects (see chapter Sn2 reaction blogposts).
Sn2 reaction examples


Sn1 reaction examples


Sn1 and Sn2 reactions in biology, nature and medicines

S-Adenosyl methionine
This is a biological methylating agens, also known as SAM.
It is a frequently used cosubstrate involved in methyl transfer reactions. For more details I would suggest to look on more specified articles around this substance. A sulfide is the leaving group in this molecule.


Methyltetrahydrofolate
This is like SAM also a biological methylating agens, the amine group is the leaving group of this molecule.

Sulfur mostard
Most commonly used for Chemical Warfare. This is a very very toxic molecule and can cause severe pains and can have devastating consequenses for the body.


Temozolomide
This molecule is an alkylating agent that is used to treat aggressive brain tumors, its most famous use was for treatment of the brain tumor of Ted Kennedy.


Comments

  1. Anonymous27 July 2022 at 12:29

    Thanks for the information. I really like the way you express complex topics in lucid way. It really helps me understand it much better way. adenosyl methionine

    ReplyDelete

Post a Comment

Popular posts from this blog

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.
Post a Comment
Read more

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
Post a Comment
Read more

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.
Post a Comment
Read more