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Example Questions
Example Question #1 : Help With E2 Reactions
Which of the following sets of conditions most strongly favors an E2 elimination reaction?
Strong base, polar protic solvent, secondary electrophile
Strong base, polar aprotic solvent, tertiary electrophile
Strong base, polar aprotic solvent, primary electrophile
Strong base, polar aprotic solvent, primary electrophile
Weak base, polar aprotic solvent, tertiary electrophile
Weak base, polar aprotic solvent, tertiary electrophile
For E2 reactions a tertiary electrophile > secondary electrophile > primary electrophile. A polar aprotic solvent favors E2 (remember that polar protic solvents favor E1). A strong base is needed to undergo E2.
Example Question #511 : Organic Chemistry
A student carried out a substitution reaction in the lab using ether as a solvent. The student began with an optically pure reactant (100% (R)-configuration) and finished with an optically pure product (100% (S)-configuration).
The reaction went through which of the following mechanisms?
SN2
SN1
E1
E2
Either SN1 or SN2
SN2
SN2 reactions result in an inversion of products, thus R-configured reactants become S-configured products and vice versa. Polar aprotic solvents such as ether favor SN2 reactions.
E1 and E2 are elimination mechanisms and the question asks for a substitution mechanism. SN1 results in racemization of products, not inversion. Thus, if the reaction had gone through SN1 we would see a mixture of R and S-configuration in the products. Additionally, polar protic solvents (not aprotic like ether) favor SN1 reactions.
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