Ch 9 Substitution and Elimination Reactions of Alkyl Halides

Question 1

An Sn2 reaction is bimolecular:

Answer 1

both the alkyl halide and the nucleophile are involved in the transition state of the rate-limiting step, so the rate of the reaction depends on the concentration of both of them

Question 2

An Sn2 reaction has a one-step mechanism:

Answer 2

the nucleophile attacks the back side of the carbon that is attached to the halogen. Therefore, it takes place with inversion of configuration

Question 3

Because of steric hindrance, the relative reactivities of alkyl halides in an Sn2 reaction are

Answer 3

primary > secondary > tertiary.

Tertiary alkyl halides cannot undergo Sn2 reactions

Question 4

The relative reactivities of alkyl halides that differ only in the halogen atom are

Answer 4

RI > RBr > RCl > RF in SN2, SN1, E2 and E1 reactions

Question 5

Basicity is a measure of

Answer 5

how well a compound shares its lone pair with a proton;

Question 6

nucleophilicity is a measure of

Answer 6

how readily a species with a lone pair is able to attack an electron-deficient atom

Question 7

Protic solvents

Answer 7

H2O, ROH

Question 8

Protic solvents have a hydrogen attached to

Answer 8

an O or an N

Question 9

Aprotic solvents

Answer 9

DMF, DMSO

Question 10

In general, the stronger base is

Answer 10

a better nucleophile

Question 11

If the attacking atoms are very different in size and the reaction is carried out in protic solvent the stronger bases are

Answer 11

poorer nucleophiles, because of ion-dipole interactions between the ion and the solvent

Question 12

An Sn1 reaction is unimolecular;

Answer 12

only the alkyl halide is involved in the transition state of the rate-limiting step, so the rate of the reaction is dependent only on the concentration of the alkyl halide

Question 13

An Sn2 reaction has a two-step mechanism:

Answer 13

the halogen departs in the first step, forming a carbocation intermediate that is attacked by a nucleophile in the second step.

Question 14

Sn1 reactions of alkyl halides are solvolysis reactions, meaning

Answer 14

that the solvent is the nucleophile

Question 15

The rate of an Sn1 reaction depends on the

Answer 15

ease of carbocation formation

Question 16

An Sn1 reaction takes place with

Answer 16

razemization

Question 17

The only substitution reactions that primary and secondary alkyl halides and methyl halides undergo are

Answer 17

Sn2 reactions

Question 18

The only substitution reactions that tertiary alkyl halides undergo are

Answer 18

Sn1 reactions

Question 19

Removal of a proton and a halide ion is called

Answer 19

dehydrohalogenation

Question 20

The product of a dehydrohalogenation elimination reaction is an

Answer 20

alkene

Question 21

An E2 reaction is

Answer 21

concerted, one-step reaction in which the proton and the halide ion are removed in the same step
CH3CH2X + B: -> CH2=CH2 + +BH + X-

Question 22

E2 reaction is called

Answer 22

a dehydrohalogenation reaction

Question 23

An E2 reaction is regioselective:

Answer 23

the major product is the more stable alkene, unless the reactants are sterically hindered or the leaving group is poor

Question 24

The more stable alkene is generally the

Answer 24

more substituted alkene

Question 25

alkyl substitution increases the stability of a carbocation and

Answer 25

decreases the stability of a caranion

Question 26

An E1 reaction is a

Answer 26

two-step reaction in which the alkyl halide dissociates, forming a carbocation intermediate. Then, a base removes a proton from a carbon adjacent to the positively charged carbon
CH3CH2X -> CH3CH2+ + X- -> CH2=CH2 + +BH + X-

Question 27

An E1 reaction is regioselective:

Answer 27

the major product is the more stable alkene

Question 28

The only elimination reactions the primary and secondary alkyl halides undergo are

Answer 28

E2 reactions

Question 29

Tertiary alkyl halides undergo

Answer 29

both E1 and E2 reactions

Question 30

For alkyl halides that can undergo both the E1 and E2 reactions, the E2 is favored by

Answer 30

a strong base and E1 is favored by a weak base

Question 31

An E2 reaction is stereoselective:

Answer 31

anti elimination is favored

Question 32

In E2 reaction: if the beta-carbon has two hydrogens

Answer 32

both E and Z stereoisomers are formed: one with the largest groups on opposite sides of the double bond is formed in greater yield because it is more stable

Question 33

In the E2 reaction: if the beta carbon is bonded to only one hydrogen

Answer 33

then only one alkene is formed. Its structure depends on the structure of the alkyl halide

Question 34

An E1 reaction is stereoselective:

Answer 34

both E and Z stereoisomers are formed regardless of the number of hydrogens bonded to the beta-carbon

Question 35

In an E2 reaction, the two groups eliminated from a six-membered ring must both be in

Answer 35

axial positions

Question 36

Primary alkyl halides undergo Sn2/E2 reactions:

Answer 36

the substitution reaction is favored unless the nucleophile/base is sterically hindered

Question 37

Secondary alkyl halides undergo Sn2/E2 reactions:

Answer 37

both substitution and elimination products are formed; strong bases, bulky bases, and high temperatures favor the elimination product

Question 38

Tertiary alkyl halides undergo

Answer 38

E2 reactions with strong bases and Sn1/E1 reactions with weak bases

Question 39

Benzylic and allylic halides undergo

Answer 39

Sn1, Sn2, E1 and E2 reactions (except tertiary not Sn2)

Question 40

Vinylic and aryl halides cannot undergo

Answer 40

Sn2, Sn1, or E1 reactions

Question 41

Vinylic halides can undergo

Answer 41

E2 reactions with a strong base

Question 42

Polar solvents insulate

Answer 42

opposite charges from one another

Question 43

Increasing the polarity of the solvent decreases the rate of the reaction if

Answer 43

one or more reactants that participate in the rate-determining step are charged

Question 44

Increasing the polarity of the solvent increases the rate of the reaction if

Answer 44

none of the reactants that participate in the rate-determining step are charged

Question 45

In ether synthesis the less hindered alkyl group should be provided by the

Answer 45

alkyl halide

Question 46

If the two functional groups of a bifunctional molecule can react with each other

Answer 46

both intermolecular and intramolecular reactions can occur

Question 47

The reaction more likely to occur depends on the concentration of the bifunctional molecule and the size of the ring that would be formed in the intramolecular reaction:

Answer 47

ring size 5-6 is favored for intramolecular reactions

the higher the concentration the more intermolecular reactions