Understanding Allyl Chemistry: NBS Substitution Mechanism Explained
Explore the NBS substitution mechanism in allyl chemistry, focusing on radical and carbocation-based reactions, SN2 mechanism, factors governing product formation, and common electronic charge transfer behaviors. Discover the influence of steric hindrance and resonance in allylic site reactions.
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Presentation Transcript
A Quicky Allyl Chemistry review NBS substitution mechanism is: Radical based Carbocation based SN2 Eat dirt Doc Name this site: Allylic site Vinyl group Name this group: Low Br2 conc. (or NBS) + Br Br uv light Symmetric resonance ? C C YES NO
A Quicky Allyl Chemistry review (continued) Which is more likely to form , A or B ? A B NBS + light Br Br What factor governs the choice of B as more likely above? Minimizing steric crowding (hindrance) What is the most likely product of: NBS Br light What factor governs the choice above? Radical intermediate forms symmetric resonance
The hydrolysis reaction shown is: Radical based Carbocation based SN1 Eat dirt Doc A Quicky Allyl Chemistry review (continued) NaHCO3 + Cl H2 O basic What is(are) the carbocation(s) in the above reaction ? A C+ B + CH2 Which is kinetically favored and why? A, since + charge is on 3o site Why is B thermodynamically favored ? More substituted around double bond (Zaitsev s rule)
A Quicky Allyl Chemistry review (continued) Both the allylic carbocation and radical mechanism share what common electronic charge transfer behavior ? Both feature electron shift towards radical or carbocation site to produce alternative intermediates C+ CH CH + CH2 radical allylic shit Carbocation allylic shift What governs the formation of the most stable carbocation above ? Carbocation degree (higher is better) What two factors govern formation of the most stable radicals above ? 1) Seeks symmetric resonance 2) Minimizes steric hindrance
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