Alkene/Alkynes reactions
- Nomenclature
- Reaction mechanisms (Hydration, hydrohalogenation,
halogenation) for alkenes and alkynes. Halo-hydrin reaction of
alkenes and Alkylation of alkynes.
- Predict reagents, predict reactants, predict products.
- Focus on functional groups.
- Physical properties, acidity of alkynes.
Alkene/Alkyne naming
• Find the longest chain involved C=C and
alkyne.
• Give priority to smaller numbering of
C=C or alkyne
• Find the substituents and arrange by
alphabetical order.
• Combine substituents.
• Assign R/S and E/Z if there’s any.
Alkene/Alkyne drawing
4-cyclobutyl-cyclooctyne
• Draw parent structure.
• Draw properly in which carbon attached
to triple bond be linear.
• Draw substituent.
• Add substituent by numbering across
triple bond.
Alkene/Alkyne drawing
4-cyclobutyl-cyclooctyne
• Draw parent structure.
• Draw properly in which carbon attached
to triple bond be linear.
• Draw substituent.
• Add substituent by numbering across
triple bond.
Alkene/Alkyne drawing
1-(2-methylcyclopentyl)-1-octyne
• Draw parent structure.
• Draw substituent.
Halogenation and Halohydrin reactions
Bromination and Halohydrin reactions mechanism
Halo-hydrin reaction
Alkene reactions (functional group changes)
Hydrohalogenation and Hydration H2O
Alkoxylation
Carbocation rearrangement
• Vinyl group or C=C attach to a tertiary C or quarternary C.
• H (tertiary C) or CH3/Alkyl (quarternary C) shift to form more stable carbocation.
• Applicable to hydration, hydro-halogenation, alkoxylation.
Carbocation rearrangement
Carbocation/Ring expansion
• Vinyl group or C=C attach to a quarternary C.
• Bond shift to form more stable carbocation.
Hydroboration, BH3/THF or B2H6, R2BH
• OH preferred less substituted site.
• No rearrangement.
• H and OH always cis to each others, syn addition, resulting
trans-product (CH3 and OH trans to each others) in this case.
Epoxidation, hydrogenation
• Same side for epoxide, syn addition.
• H is cis to each other for hydrogenation, syn addition.
Ozonolysis
• Cut double bond off.
• Add O to each side.
• Mono-substituted side gives aldehyde. Di-substituted side gives ketone
Alkene reactions practice
Alkene reactions practice
Halo-hydrin practice
What’s the major product/s?
What’s the major product/s?
Alkyne reactions
Alkene and Alkynes additions
Bromination/Halogenation of alkene/alkynes mechanism
Hydro-halogenation, HCl, HBr of alkene/alkyne mechanism
Hydration H2O mechanism
Hydrogenation of alkynes
Don’t confuse by both of these
Alkylation of terminal alkynes
Don’t confuse by both of these
Alkylation of terminal alkynes
1. 2 steps reaction.
2. Step one involves deprotonation of acidic terminal alkyne proton.
3. Step 2 involves nucleophilic substitution reaction in which the carbanion attacks the
electrophile alkylbromide.
4. The electrophile has to be primary halides.
Alkenes vs Alkyne reactions
Reagents
Alkene
Alkynes
H3O+/H2O
Alcohol, more substituted
Ketone, more substituted
1.BH3, 2.NaOH/H2O2
Alcohol, less substituted
Aldehyde, less substituted
HCl or HBr
Cl or Br on more substituted
Cl or Br on more substituted. If 2eq
or more, 2x Cl or Br on more
substituted.
Br2 or Cl2
trans-dibromide or dichloride
trans-dibromide or dichloride. If
2eq or more, 4 Cl or Br across 2
carbons.
Stereo and Regioselectivity
Reagents
Stereoselective
H3O+/H2O
1.BH3, 2.NaOH/H2O2
Regioselective
Markovnikov
Syn-addition
HCl or HBr
Anti-Markovnikov
Markovnikov
Br2 or Cl2
Anti-addition
Br2 and H2O
Anti-addition
Markovnikov
Cl2 and H2O
Anti-addition
Markovnikov
mCPBA
Syn-addition
H2/Pd or Ni or Pt
Syn-addition
Example of questions
Example of questions
Alkylation of terminal alkynes, which combo?
Multiple choice questions
1. Most stable carbocation?
Multiple choice questions
1. Most stable carbocation?
Multiple choice questions
1. Rank increasing acidity (from
least acidic to most acidic)?
Multiple choice questions
1. Which one follows anti-Markovnikov?
2. Which one will give H-shift or rearranged product?
Multiple choice questions
1. Which will give syn product?
2. Which will give 2 diastereomers?
Multiple choice questions
1. Which will NOT give 2 products?
2. Which will NOT have ketone product?
GOOD LUCK! Have a
great holiday!