CHM 206 FINAL UPDATED ACTUAL QUESTIONS AND CORRECT ANSWERS

CHM 206 FINAL UPDATED ACTUAL QUESTIONS AND
CORRECT ANSWERS

Question:
1. In NaI and AgNO3, why does 2-bromobutane react faster than 2-chlorobutane?
Answer:
Br is a better leaving group, C-Br bond is longer than C-Cl

Question:
2. Why does benzyl chloride react under SN1 and SN2?
Answer:
Benzylic halide, easier to leave and maintain stabilization due to resonance. SN1- carbocation stabilized,
SN2 - primary alkyl halide

Question:
3. Why is bromobenzene non-reactive under both SN1 and SN2?
Answer:
Bromobenzene is unreactive due to steric hindrance from the ring and pi bond interactions (sp2) that pull
the electrons closer to the ring. The carbocation is very unstable in SN1.

Question:
4. Benzyl chloride and 1-chlorobutane are both primary alkyl chlorides, but in NaI, benzyl chloride reacts
much faster, why?
Answer:
Benzyl chloride contains an aromatic/benzylic system, which allows the benzylic carbocation intermediate
to maintain stability and form faster. 1-chlorobutane cannot achieve stability as quickly when chlorine
leaves the compound.

Question:
5. To substitute bromine with a nucleophile, would it be SN1 or SN2 for 1-methyl-bromocyclohexane?
Answer:
SN1 because it's a tertiary cyclic alkyl halide

Question:
6. To substitute bromine with a nucleophile, would it be SN1 or SN2 for 1-bromopropane?
Answer:
SN2 because it's as primary halide, available for nucleophilic attack, least substituted

Question:
7. To substitute bromine with a nucleophile, would it be SN1 or SN2 for 2-bromohexane?
Answer:
Can react as both, lacks steric hindrance and is secondary alkyl halide. Prefer SN2 due to steric hindrance,
prefer SN1 for secondary position, might slightly favor SN1

, Question:
8. Rank the speed of reactivity of 5-bromo-1,3-pentadiene, bromocyclopentane, 2-bromo-2-methylhexane
Answer:
5-bromo-1,3 pentadiene > 2-bromo-2-methylhexane > bromocyclopentane, 5-bromo-1,3 pentadiene is
fastest because of conjugated double bonds (better stabilization via electron delocalization),
2-bromo-2-methylhexane is next because stable tertiary carbocation, bromocyclopentane goes through a
secondary carbocation, least stable

Question:
9. Why does bromocyclohexane react faster than chlorocyclohexane in an SN2 reaction?
Answer:
Bromine is a better leaving group because it's a weaker base

Question:
10. T/F: To promote the SN1 mechanism, you used AgNO3 in a polar, protic solvent.
Answer:
True, A protic, polar solvent is used in SN1 reaction to help with the dissociation of the halogen via
stabilization and solvation of the resulting ions and the creation of a carbocation.

Question:
11. T/F: The rate of reaction for the SN2 mechanism is dependent on the concentration of both nucleophile
and the electrophile.
Answer:
True, Since the reaction rate of a SN2 depends on both the substrate and the nucleophile, it follows second
order kinetics. The SN2 reaction occurs when a nucleophile collides effectively with the alkyl halide and
this collision rate is increased if either one (or both) of the reactants is increased. The nucleophile needs to
be strong since it follows second order kinetics and not first order kinetics where only the substrate is
accounted for.

Question:
12. Does Zaitsev's rule come to play during the reaction carried in this experiment?
Answer:
No, cyclohexanol is symmetrical and both beta-carbons are equivalent, they have the same number of
hydrogens bonded to them

Question:
13. T/F: The E1 mechanism is a one-step mechanism
Answer:
False, it's two step, the rate order is first order, unimolecular

Question:
14. Between 1-phenyl-1-propanol and 1-cyclohexyl-1-propanol, which one is more reactive under
H3PO4/aqueous conditions?
Answer:
1-phenyl-1-propanol would be more reactive under these conditions because it forms a benzyl carbocation
as opposed to a secondary carbocation. The benzyl carbocation can stabilize the carbocation intermediate
better due to its pi bonds allowing resonance stabilization.