Chapter 8 - Substitution and Elimination

Question 1

Why is I a better leaving group in comparison to Cl, Br, and F?

Answer 1

Large size

better leaving group in order

F < Cl < Br < I

Question 2

Which reaction will give a racemic mixture

a) SN1
b) SN2
c) E1
d) E2

Answer 2

A

Question 3

Differentiate between SN1 and SN2 reactions in regards to:

• weak or strong nucleophiles
• stereochemistry of the product
• whether rearrangement can occur

Answer 3

SN1 - weak nucleophile, no stereochemistry involved, gives racemic products, rearrangement possible

SN2 - strong nucleophile, inversion of stereochemistry, no carbocation formation

Question 4

When trying to determine if a reaction is SN1 or SN2, how can you differentiate between a strong or weak nucleophile?

Answer 4

strong nucleophile = resonance stabilized or has a negative charge

weak nucleophile = lone pairs

Question 5

What is the rate for SN1 and SN2 reactions?

Answer 5

SN1: rate = k [electrophile]

SN2: rate = k [electrophile][nucleophile]

Question 6

Halogens prefer to do ____ reactions

Answer 6

SN1

Question 7

T/F? Rearrangements happen in both E1 and E2 reactions

Answer 7

FALSE - they can only happen in E1

Question 8

E1 and E2 reactions will usually give the Zaitsev’s product. In what condition will either reaction yield the anti-Zaitsev?

Answer 8

If a bulk base is used

Question 9

In E2 reactions, the H being plucked off by the strong base must be in what type of formation?

Answer 9

anti-coplanar to the leaving group

Question 10

How do you determine if the nucleophile or base is acting as a nucleophile or a base?

What is the exception to this rule?

Answer 10

If it’s bigger than CH3CH2OH = elimination (acts as a base)

smaller than CH3CH2OH = substitution (acts as a nucleophile)

acetate is bigger than ethanol, but it prefers to do substitution