Nucleophilic Reactions

Question 1

Nucleophiles

Answer 1

Nucleophiles donate electrons and are Lewis bases.

The best nucleophiles are usually strong bases, and higher electronegativity means worse nucleophilicity.

Question 2

Electrophiles

Answer 2

Electrophiles are usually positively charged or polarized.
Carbonyl groups are common electrophiles.

Question 3

Good leaving groups

Answer 3

Leaving groups are the group that is removed in a nucleophilic substitution reaction
Weak bases make good leaving groups, especially halogen gases like Cl- and Br- since they avoid competing in a reverse reaction.

Question 4

Poor leaving groups

Answer 4

Stronger bases like OH- are poor leaving groups because they are not stable after leaving the molecule

Question 5

Nucleophilic substitution Sn1 vs Sn2

of steps

Answer 5

Sn1: Two steps

Sn2: One step

Question 6

Nucleophilic substitution Sn1 vs Sn2

Principle

Answer 6

Sn1: First, carbocation formed as LG leaves, THEN nucleophile attacks either side

Sn2: “Backside attack” of nucleophile simultaneous with LG leaving

Question 7

Nucleophilic substitution Sn1 vs Sn2

Rate law

Answer 7

Sn1: Unimolecular: Rate = k [substrate]

Sn2: Bimolecular: Rate = k [substrate] [nucleophile]

Question 8

Nucleophilic substitution Sn1 vs Sn2

Limiting factor

Answer 8

Sn1: Stability of carbocation

Sn2: Steric hindrance

Question 9

Nucleophilic substitution Sn1 vs Sn2

Preferred carbon

Answer 9

Sn1: Tertiary or secondary carbon

Sn2: Primary carbon (less hindered)

Question 10

Nucleophilic substitution Sn1 vs Sn2

Solvent

Answer 10

Sn1: Polar protic (ie alcohols, acetate)

Sn2: Polar aprotic (ie DMSO or acetone)

Question 11

Nucleophilic substitution Sn1 vs Sn2

Strength of nucleophile

Answer 11

Sn1: Weak (usually neutral)

Sn2: Strong (usually negatively charged)

Question 12

Nucleophilic substitution Sn1 vs Sn2

Stereochemistry of products

Answer 12

Sn1: Racemic mixture of retained/inverted

Sn2: Inverted