Alkyl Halides Flashcards
(12 cards)
List the ways to synthesize Alkyl Halides
- Hydrohalogenation
- Halogenation
- Halogenation
- Substitution of alcohols:
a) Using tertairy alcohols: Uses strong acid (HCl or HBr) in anhydrous conditions (ether solvent) Happen via SN1
b) using secondary and Primary alcohols : uses thionyl Chloride (SOCl2) or Phosphorous tribromide (PBr3) in anhydrous conditions
When alkyl halides participate in nucleophilic Substitution reactions are they the nucleophile or electrophile?
electrophile (specifically the Carbon).
In an Sn2 reaction, the inversion of configuration occurs (its a stereospecific reaction). Why is this?
The nucleophile attacks from the backside of the electrophilic carbon, opposite the leaving group
Sn2 Reactions are most reactive for methyl/primary/secondary/tertiary substrates. Why?
Methyl and primary. Less steric hinderance, nucleophile can easily attack.
What are the beast leaving groups for Sn2 reactions? why?
weak bases e.g, F-, Cl-. (conjugate bases of strong acids). they can stabilize the electron pair taken from sigma bond.
Weaker bonds of C-X also makes for a better leaving group
What makes a good nucleophile for Sn2 reactions?
strong bases because they readily donate electrons for form new sigma bond.
Why do Sn1 reactions result in a racemic mixture?
the carbocation formed is planar (sp2 hybridized) i.e its an achiral carbocation intermediate. This allows nucleophile to attack from either side with equal probability. BOTH ENATIOMERS ARE FORMED
what makes a good LG and Nucleophile for Sn1 reactions
much the same as Sn2, must be able to accommodate electron pair. Nucleophile strength isnt as important, rate depends more on carbocation stability and LG)
Elimination reactions: removal of substituent to form double or triple bonds. The nucleophile is a proton acceptor (strong base) as opposed to electron donor (such as in sub). This means nucleophile will snatch a H from the substrate and pi bond will form.
slay
what is Zaitsevs rule
must substituted alkene predominates, pi bond will form between alpha-carbon and beta-carbon with the most substituents. The nucleophile will snatch a beta-hydrogen
briefly explain how E1 reactions proceed
leaving group leaves, strong base attacks beta-H, pi bond form between beta-C and alpha-C
briefly explain how E2 reaction proceed
strong base attacks beta H, leaving group leaves, pi bond formed
