Electrophilic Additions

Question 1

Addition Reacitons

Answer 1

• two molecules become one - reagent adds to substrate
• characteristic reactions of unsaturated compounds
• nucleophile “attacks” electrophile

Question 2

HX Addition Mechanism

Answer 2

1. C=C attack on H-X, formation of C-H sigma bond & C+

2. X- attack on C+, formation of C-X sigma bond

Question 3

Key Features of HX additions

Answer 3

1. “Either side attack” -C=C can approach H+ from left or right & X- can approach C+ from left or right
2. “Scrambling of Configuration” - new sp3 carbons in product are racemic
3. “Markovnikov Addition” - regioselective, most stable C+ intermediate

Question 4

Markovnikov’s rule

Answer 4

• in the addition of HX to C=C, the H (or any E-) adds to the carbon witht he most Hs already TO MAKE THE MOST STABLE CARBOCATION
• carbocation stability:
  tertiary > secondary > primary

Question 5

Carbocation rearrangements

Answer 5

• unstable carbocations can rearrange to form more stable carbocations
• 1,2 alkyl or hydride shift (migrates with its pair of electrons)
• Original site of shifting group attachment becomes new carbocation

Question 6

HX Addition Mechanism to Alkynes

Answer 6

1. C(triple)C attack on H-X formation of C-H sigma bond and C+
2. X- attack on C+, formation of C-X sigma bond
   REPEAT STEPS 1 AND 2 ON NEW ALKENE PRODUCT

Question 7

Key Features of HX Additions

Answer 7

1. “Either side attack” –C≡C/C=C can approach H+from left or right & X-can approach C+ from left or right
2. “Scrambling of Configuration” – new sp3 carbons in product are achiral
3. “Markovnikov Addition” –regioselective, most stable C+ intermediate

Question 8

HX (WITH ROOR) Addition Mechanism

Answer 8

1. RO• attack on H-X, formation of RO-H σbond & X•
2. C=C attack on X•, formation of C-Xσbond and C•
3. C• attack on H-X, formation of C-Hand X• (repeat from step 2)

Question 9

Anti-Markovnikov Addition

Answer 9

• The H (or any E+) adds to the carbon with the least H’s already TO MAKE THE MOST STABLE FREE RADICAL
• Carbon radical stability:
  tertiary > secondary > primary

Question 10

Key Features of HX (with ROOR) Additions

Answer 10

1. “Either side attack” –C=C can approach X• from left or right & C• can approach H-X from left or right
2. “Scrambling of Configuration” –new sp3 carbons in product are racemic
3. “Anti-Markovnikov Addition” –regioselective, most stable C• intermediate

Question 11

H2O Addition Mechanism

Answer 11

1. C=C attack on H-X, formation of C-H σ bond & C+
2. H2O attack on C+, formation of C-OH2 + σbond (more H2O than X-)
3. C-OH2+ loses H+ to water/solvent

Question 12

Markovnikov’s Rule (H2O addition)

Answer 12

in the addition of HOH to C=C, the H (or any E+) adds to the carbon with the most H’s already TO MAKE THE MOST STABLE CARBOCATION

Question 13

Key Features of H2O additions

Answer 13

1. Either side attack” –C=C can approach H+from left or right & H2O can approach C+from left or right
2. “Scrambling of Configuration” –new sp3 carbons in product are racemic
3. “Markovnikov Addition” –regioselective, most stable C+intermediate