Quiz - Alkyl Halides - Eliminations | Alkyl Halides - Elimination Reactions

1

Which statement is correct about a SN1 reaction?

The reaction is stereospecific

The bond-breaking step is the fastest step of the reaction

SN1 reactions proceed through an intermediate carbocation

The kinetic rate involves the nucleophile

SN1 reactions are​​​​​​​ nucleophilic substitutions which proceed through an intermediate carbocation ⇒ SN1 reactions are unimolecular with a bond-breaking step following by a bond-making step. The bond-breaking step is slower and therefore determines the rate: it is the rate-determining step

2

Which of the following statements regarding the E2 mechanism is incorrect?

E2 mechanism is always bimolecular

E2 mechanism is second order

E2 mechanism occurs in one step

E2 mechanism occurs with a syn periplanar geometry

E2 reactions are nucleophilic eliminations which do not proceed via an intermediate ⇒ E2 reactions are bimolecular with simultaneous bond-making and bond-breaking steps. E2 reactions always occur with an anti periplanar geometry (preferred over syn periplanar geometry)

3

Which statement is incorrect about an E1 reaction between (CH3)3CBr and NaOH?

It competes with an SN1 reaction

An alkene is formed

The reaction occurs with an anti periplanar geometry

The kinetic rate only involves (CH3)3CBr

Due to planar carbocation, E1 reactions do not always occur with an anti periplanar geometry
SN1 and E1 reactions always compete

4

Which of the following starting materials most likely reacts via an E1 mechanism?

CH3CH2I

CH3CH2Br

(CH3)2CHBr

(CH3)3CBr

The more stable the carbocation intermediate, the faster the E1 reaction. A tertiary carbocation is more stable than a secondary or a primary (hyperconjugation) ⇒ (CH3)3CBr will react via an E1 mechanism

5

What is the major product of an elimination reaction between 3-chloro-2,3-dimethylpentane and NaOH?

2,3-dimethylpent-2-ene

3,4-dimethylpent-2-ene

2-methyl-3-methylenepentane

No selectivity observed

In elimination reactions, the major product is the most substituted alkene. This is the Zaitsev's rule

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6

Which conditions favor an E1 reaction?

Strong sterically hindered base / primary alkyl halide

Strong sterically hindered base / tertiary alkyl halide

Good nucleophile / primary alkyl halide

Good nucleophile / tertiary alkyl halide