Reaction Mechanisms

Question 1

What type of alcohol (1˚, 2˚, 3˚) is most likely to undergo Sn1 in the presence of acid?

Answer 1

Tertiary alcohol

• Becomes tertiary carbocation (most stable)

Question 2

Sn1

Answer 2

• Unimolecular transition state
• Forms carbocation
• Two step mechanism

Question 3

Sn2

Answer 3

• Bimolecular transition state (LG and Nu)
• Does not form carbocation
• One step mechanism

Question 4

Which type of carbon (primary, secondary, tertiary) is most reactive for SN1?

Answer 4

Tertiary is more reactive b/c tertiary carbocation that forms is more stable

Question 5

Which type of carbon (primary, secondary, tertiary) is most reactive for SN2?

Answer 5

Primary is more reactive b/c less steric hindrance for Nu attack

Question 6

Retention of absolute configuration (SN1)

Answer 6

Nu attacks same side that LG was on (

Question 7

Inversion of absolute configuration

Answer 7

Nu attacks opposite side of LG

• > 50% for SN1 b/c no LG shielding
• Always the case for SN2
• R becomes S and vice versa

Question 8

How to make OH a good LG?

Answer 8

• Protonate w/ acid

- Tosylate w/ TsCl and Pyr => OTS

Question 9

Alkyne + H2/Lindlar Pd

Answer 9

Forms cis alkene w/ syn addition

• Lindlar Pd = “poisoned” => stops reaction after alkene is formed (does not make alkane)

Question 10

Alkyne + Na/NH3

Answer 10

Forms trans alkene w/ anti addition

• Forms radical carbon anion

Question 11

Alkyne + H2/Pt

Answer 11

Reduces alkyne => alkene => alkane

• Not poisoned => doesn’t stop after alkene

Question 12

Combustion reaction of hydrocarbon forms ____ and _____

Answer 12

H2O and CO2

Question 13

What order kinetics is Sn1?

Answer 13

First order

• Depends on LG leaving to form carbocation

Question 14

Strong base + alkyl halide => _____

Answer 14

Deprotonate alkyl halide => alkene