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CHEM 109B MIDTERM 1 Questions and
Correct Answers/ Latest Update / Already
Graded
Effects of sterics on the rate of a SN2 reaction
Ans: Rate decreases as steric hindrance increases
What kind of alkyl halides undergo SN2
Ans: Methyl, primary, and secondary
What makes a good leaving group (aprotic)
Ans: A weak (stable) base
What is the configuration of products in SN2
Ans: Inverted product only
What is the configuration of products in SN1
Ans: Inverted and retained configurations
What is the effect of a strong Nu- on the rate of SN1 and SN2
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Ans: a strong Nu- has no effect on SN1 because it does not
take part in the rate determining step.
A strong Nu- increases the rate of reaction in SN2
What is the general mechanism of an E2 reaction like
Ans: ALL ONE STEP
- a strong base removes a H from a beta-carbon
- the e- from the previous H-C bond form a double bond
between the alpha and beta carbon
- the leaving group leaves
Dehydrohalogenation
Ans: Removal of a proton and halide ion
Alpha-carbon:
Ans: The carbon to which the halogen is attached
Beta-carbon
Ans: The carbon(s) adjacent to the alpha-carbon from which a
H will be removed in a elimination reaction
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What is an elimination reaction initiated by
Ans: The removal of a proton from a beta-carbon
Which beta-carbon in an E2 reaction is a hydrogen usually eliminated
from
Ans: The beta-carbon that is bonded to the fewest hydrogens
Which beta-carbon in an E2 reaction is a hydrogen usually eliminated if
the reaction has a bulky base and if its approach to the alkyl halide is
sterically hindered and why
Ans: A hydrogen will be removed from the beta-carbon who's
hydrogen are most easily accessible because of steric
hindrance, usually the more unstable alkene will be formed
What happens in an E2 reaction that begins with an alkyl fluoride?
Why?
Ans: The less stable alkene will be formed because F is a poor
leaving group. As H is removed, F is slower to leave so it will
remove the H that is further away from it, usually from the
Beta-carbon with more H
What are carbocations stabilized by
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Ans: Stabilized by hyperconjugation and e- donating alkyl
groups
Relative reactivity of alkyl halides in E2
Ans: 3 > 2 > 1
What is the general mechanism of an E1 reaction
Ans: 2 STEPS
1. leaving group leaves and carbocation forms
- carbocation arrangement if possible
2. Relatively weak base removes H from B-carbon and the e-
from that bond form a double bond between the B-carbon and
A-carbon
Which alkyl halides undergo only E2
Ans: Primary and secondary
What elimination reactions do tertiary alkyl halides undergo
Ans: E2 - when there is a strong or bulky base
E1 - when there is a weak base
All rights reserved © 2025/ 2026 |
CHEM 109B MIDTERM 1 Questions and
Correct Answers/ Latest Update / Already
Graded
Effects of sterics on the rate of a SN2 reaction
Ans: Rate decreases as steric hindrance increases
What kind of alkyl halides undergo SN2
Ans: Methyl, primary, and secondary
What makes a good leaving group (aprotic)
Ans: A weak (stable) base
What is the configuration of products in SN2
Ans: Inverted product only
What is the configuration of products in SN1
Ans: Inverted and retained configurations
What is the effect of a strong Nu- on the rate of SN1 and SN2
All rights reserved © 2025/ 2026 |
, Page |2
Ans: a strong Nu- has no effect on SN1 because it does not
take part in the rate determining step.
A strong Nu- increases the rate of reaction in SN2
What is the general mechanism of an E2 reaction like
Ans: ALL ONE STEP
- a strong base removes a H from a beta-carbon
- the e- from the previous H-C bond form a double bond
between the alpha and beta carbon
- the leaving group leaves
Dehydrohalogenation
Ans: Removal of a proton and halide ion
Alpha-carbon:
Ans: The carbon to which the halogen is attached
Beta-carbon
Ans: The carbon(s) adjacent to the alpha-carbon from which a
H will be removed in a elimination reaction
All rights reserved © 2025/ 2026 |
, Page |3
What is an elimination reaction initiated by
Ans: The removal of a proton from a beta-carbon
Which beta-carbon in an E2 reaction is a hydrogen usually eliminated
from
Ans: The beta-carbon that is bonded to the fewest hydrogens
Which beta-carbon in an E2 reaction is a hydrogen usually eliminated if
the reaction has a bulky base and if its approach to the alkyl halide is
sterically hindered and why
Ans: A hydrogen will be removed from the beta-carbon who's
hydrogen are most easily accessible because of steric
hindrance, usually the more unstable alkene will be formed
What happens in an E2 reaction that begins with an alkyl fluoride?
Why?
Ans: The less stable alkene will be formed because F is a poor
leaving group. As H is removed, F is slower to leave so it will
remove the H that is further away from it, usually from the
Beta-carbon with more H
What are carbocations stabilized by
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, Page |4
Ans: Stabilized by hyperconjugation and e- donating alkyl
groups
Relative reactivity of alkyl halides in E2
Ans: 3 > 2 > 1
What is the general mechanism of an E1 reaction
Ans: 2 STEPS
1. leaving group leaves and carbocation forms
- carbocation arrangement if possible
2. Relatively weak base removes H from B-carbon and the e-
from that bond form a double bond between the B-carbon and
A-carbon
Which alkyl halides undergo only E2
Ans: Primary and secondary
What elimination reactions do tertiary alkyl halides undergo
Ans: E2 - when there is a strong or bulky base
E1 - when there is a weak base
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