CHEM 109B MIDTERM 1 EXAM
QUESTIONS AND ANSWERS 100% PASS
2026/2027
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 - 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
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1
,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
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 - 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
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2
, - 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
Which elimination reaction requires the L.G and the leaving proton to both be in the anti
position - ANS E2
What are the products of an E2 reaction in which the proton that is removed is from a b-carbon
that originally had 2 H in the reactants - ANS Both E and Z are formed
What are the products of an E2 reaction in which the proton that is removed is from a b-carbon
that originally had 1 H in the reactants - ANS 1 stereoisomer formed whose configuration is
dependent on the reactant
What is the stereochemistry of the products of an E1 reaction - ANS Both E and Z formed but
the major product is the one with the largest groups on opposite sides of the double bond
What has to occur in an E2 reaction of cyclohexanes - ANS Both groups being removed must
be parallel so both groups must be in axial, even if the b-hydrogen that is being removed didn't
have the most H on it
Relative reactivities of SN2 - ANS 1>2>3
What kind of product will the reaction of a 1 alkyl halide with a Nu-/base that is not sterically
hindered - ANS Mostly substitution
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QUESTIONS AND ANSWERS 100% PASS
2026/2027
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 - 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
2026/2027 ALLRIGHTS RESERVED
1
,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
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 - 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
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2
, - 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
Which elimination reaction requires the L.G and the leaving proton to both be in the anti
position - ANS E2
What are the products of an E2 reaction in which the proton that is removed is from a b-carbon
that originally had 2 H in the reactants - ANS Both E and Z are formed
What are the products of an E2 reaction in which the proton that is removed is from a b-carbon
that originally had 1 H in the reactants - ANS 1 stereoisomer formed whose configuration is
dependent on the reactant
What is the stereochemistry of the products of an E1 reaction - ANS Both E and Z formed but
the major product is the one with the largest groups on opposite sides of the double bond
What has to occur in an E2 reaction of cyclohexanes - ANS Both groups being removed must
be parallel so both groups must be in axial, even if the b-hydrogen that is being removed didn't
have the most H on it
Relative reactivities of SN2 - ANS 1>2>3
What kind of product will the reaction of a 1 alkyl halide with a Nu-/base that is not sterically
hindered - ANS Mostly substitution
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