chapter 11

Question 1

hydrohalogenation

Answer 1

• addition of HX (Cl, Br, I)
• 2 equiv
• H bonds to less substituted Carbon

1. H is deprotonated from HX and carbocation is formed
2. X atom bonds to carbocation –> vinyl halide
3. H is deprotonated from HX and carbocation forms
4. X atom bonds to carbocation –> geminal dihalide

Question 2

halogenation

Answer 2

• addition of X2(Cl, Br)
• 2 equiv
• bridged halonium intermediates
• anti addition of X2

1. bridged halonium ion X+
2. nucleophilic attack of X-
   - makes trans dihalide
3. bridged halonium ion X+
4. nucleophilic attack of X-
   - tetrahalide is formed

Question 3

hydration

Answer 3

• addition of OH and H
• H2O combines with H20, H2SO4, HgSO4 to make H3O
• H bonds to less sub. Carbon

1. H3O is deprotonated and carbocation forms
2. H2O bonds to carbocation
3. H2O is deprotonated by H2O –> enol is formed
4. tautomerization:
   - H3O is deprotonated and carbocation forms
5. movement of electrons to make C=OH
6. OH is deprotonated from H2O –> ketone is formed

Question 4

hydroboration-oxidation

Answer 4

• addition of H20
• uses (1) BH3/ (2) H202, -OH
• BH2 bonds to less sub. C atom
• unstable enol formed after oxidation then rearranges to a carbonly group and makes a aldehyde (R-CH2-CH=O)

1. H and BH2 are added –> BH2 good LG
2. OH bonds –> enol is formed
3. Tautomerization:
   - addition of H and C=O bond forms –> aldehyde is formed

Question 5

Acetylene (ethyne)

Answer 5

HC-triple bond-CH

Question 6

enol tautomer vs keto tautomer

Answer 6

enol - has O-H bonded to C=C
RHC=C(OH)R

keto - has C=O and additional C-H bond
R-CH2-C=O-R

Question 7

what is a tautomer?

Answer 7

Constitutional isomer that differs in location of a double bond and H atom

• equilibrium favors keto by C=O is stronger