Page 18 Flashcards
What types of bases are commonly used in E2 reactions?
A: Strong, negatively charged bases such as \text{OH}^- and \text{OR}^- .
How does the strength of the base affect the rate of an E2 reaction?
A: The rate of the E2 reaction increases as the strength of the base increases.
Why does the base appear in the rate equation for E2 reactions?
A: Because the base participates directly in the rate-determining step.
What are two sterically hindered nitrogen bases used in E2 reactions?
A: DBN (1,5-diazabicyclo[4.3.0]non-5-ene) and DBU (1,8-diazabicyclo[5.4.0]undec-7-ene).
What is the structural feature of DBN and DBU that makes them effective in E2 reactions?
A: Their steric hindrance and strong basicity make them selective for deprotonation without nucleophilic substitution.
What is the role of the base in the E2 reaction mechanism?
A: The base abstracts a proton from the β-carbon, facilitating the formation of the double bond.
Why are sterically hindered bases like DBN and DBU preferred in some E2 reactions?
A: They reduce the likelihood of competing substitution reactions (e.g., S_N2 ).
What effect does a sterically hindered base have on E2 selectivity?
A: It increases the likelihood of elimination over substitution, favoring E2 products.
How do strong bases like \text{OH}^- and \text{OR}^- interact with the substrate in an E2 reaction?
A: They remove a β-hydrogen, leading to the simultaneous departure of the leaving group and formation of a π bond.
In what types of substrates are DBN and DBU particularly useful for E2 reactions?
A: Substrates with bulky groups where steric hindrance might impede smaller bases.
