Sn Reactions

Question 1

what are common and very reactive intermediates?

Answer 1

• carbocation R₃C+
• Carbanion R₃C-
• Radical R₃C ^.
• carbene R₂C

Question 2

What types of reactions are there?

Answer 2

• substituition reactions
• addition reactions
• elimination reactions

Question 3

What is a nucleophile?

Answer 3

nucleous loving

• rich in electrons
• ready to donate a lone pair

Question 4

What is an electrophile?

Answer 4

electron loving

• poor in electron
• accepts electron pairs

Question 5

What is a HOMO-LUMO interaction?

Answer 5

Overlap of HOMO of nucleophile and LUMO of electrophile leads to formation of a new bond (new MO)

Question 6

What is a heterolytic cleavage?

Answer 6

bond cleavage where both electrons remain on one partner

Question 7

What is a Homolytic cleavage

Answer 7

one electron for every partner (radicals formed)

Question 8

is Sn1 is one two step mechanism?

Answer 8

Sn1 is a 2 STEP mechanism

Question 9

is Sn2 is a one or two step mechanism?

Answer 9

Sn2 is a ONE STEP mechanism (bimolecular rate determining step)

Question 10

What does the reaction rate of an Sn1 reaction depend on?

Answer 10

concentrationof starting material. NOT the Nucleophile

Question 11

What does the reaction rate of an Sn2 reaction depend on?

Answer 11

on both starting material and nucleophile

Question 12

What is the most comming leaving group in Sn reactions?

Answer 12

Halides

Question 13

Why are aprotic polar solvents preferred in Sn2 mechanisms?

Answer 13

• aprotic polar solvent helps stabilizing cation of reactant (separates cation from nucleophile)
• increaseses effectiveness of nucleophile
• nucleophile will not be solvated (therefore no steric hinderance for nucleophile to attack)

Question 14

What polar solvents are preferred in an Sn1 reaction?

Answer 14

polar PROTIC solvents

Question 15

What polar solvents are preferred in an Sn2 reaction?

Answer 15

polar APROTIC SOLVENT

Question 16

why are polar protic solvents preferred in an Sn1 reaction?

Answer 16

• protic solvents help to stabilize the carbocation
• they are usually more polar so help to remove the leaving group and stabilize it

Question 17

Is OH- or water a better nucleophile?

Answer 17

The stronger base = stronger nucleophile

• OH- > H2O

Question 18

Is CH3O– or CH3OH a stronger nucleophile

Answer 18

stronger bases are stronger nucleophiles

• CH3O– > CH3OH

Question 19

Is CH3CH2NH– or CH3CH2NH2 a stronger nucleophile?

Answer 19

stronger base is a stronger nucleophile

• CH3CH2NH– > CH3CH2NH2

Question 20

Under Sn1 conditions, does the harder or softer nucleophile react? more or less electronegative?

Answer 20

the Harder, hence high electronegativity

Question 21

Under Sn2 conditions, does the harder or softer nucleophile react? high or low electronegativity?

Answer 21

Sn2

• soft nucleophile (low electronegativity)

Question 22

What are examples of good leaving groups?

Answer 22

• Cl-, Br-, I-, Sulfonate (RSO3-), Sulfate (ROSO3-), Phosphate
• H2O, ROH, Amines, Phosphines

good leaving groups are BAD nucleophiles

Question 23

What carbons do not undergo Sn reactions?

Answer 23

Aryl and Vinylhalides do not do SN reactions

Question 24

Do we have inversion or retention stereochemistry in Sn1?

Answer 24

in Sn1, we can get both Inversion and retention stereochemistry

Question 25

Do we have inversion or retention stereochemistry in Sn2?

Answer 25

In Sn2 we only have inversion stereochemistry