Major product

Dr. Clower
CHEM 2411
Spring 2014
McMurry (8th ed.) sections 7.7-7.8, 7.10-7.11, 10.3-10.4,
8.2-8.8, 8.10, 8.12, 9.3-9.8, 7.1, 8.1, 9.2, 9.9
• Reactions of alkenes
• Reactions of alkynes
• Preparation of alkenes and alkynes
• Synthesis
• No reactions of alkyl halides (originally on syllabus)
Reaction Charts
• Help organize reaction details
• Organize charts by reaction
type, starting material, product
• See webpage for template
• Example:
Reaction Type
1. Hg(OAc)2, H2O
2. NaBH4
Anti addition
Reactions of Alkenes
Allylic halogenation
Electrophilic addition
I. Allylic Halogenation
• Similar to radical halogenation of alkanes
• Alkene react with molecular halogen in the presence of
heat or light
• Alkyl halide is produced
• Substitution of –X for –H at the allylic position
• Most stable radical intermediate
• Stabilized by resonance
Allylic Halogenation
• Another set of reagents:
• N-bromosuccinimide (NBS), hn
• Bromination only (no chlorination)
• Product is a racemic mixture (if there is a stereocenter)
Radical Stability
• What is the major product of the reaction of 1-octene with
NBS (in the presence of light)?
• What is the major product of the reaction of 1-octene with
NBS (in the presence of light)?
• Reaction occurs at less sterically hindered carbon and
produces the more stable C=C
• What is the major product of the following reaction?
II. Electrophilic Addition
• Most common reaction of alkenes
• Examples:
• Break p bond of alkene
• Form new s bonds to each C of double bond
• Alkene is nucleophile; reacts with electrophile (HX, H2O, etc.)
• Forms carbocation intermediate
Electrophilic Addition
• General mechanism:
• Step 1:
• Step 2:
• Which step is RDS?
Addition of Hydrogen Halides
• HCl, HBr, HI
• Example: 2-methylpropene + HBr
• What is the major product of the following reaction?
• Stereochemistry of product = racemic mixture
• Carbocation intermediate is planar, sp2 hybridized
• Regiochemistry of reaction
• Which C gets the H? Which C gets the X?
• Reaction is regiospecific for one product
Regiochemistry of Electrophilic Addn.
• Markovnikov’s Rule:
• In the addition of HX (or H2O) to an alkene, the H will add to the
carbon with the greater number of H’s already bonded to it
• The X (or OH) attaches to the carbon with fewer H’s (the more
substituted carbon)
• Product = Markovnikov product
• Opposite product = anti-Markovnikov or non-Markovnikov
• Formed under specific conditions
Markovnikov’s Rule
Markovnikov’s Rule
• Why is the Markovnikov product favored?
• Look at reaction intermediate
• Carbocation
• Markovnikov addition forms the more stable R+
• 3º > 2º > 1º
• More stable carbocation forms faster, will react to give
Markovnikov’s Rule
• Draw and name the major product of the following reaction.
• Draw and name the major product of the following reaction.
• Expected product =
• Actual product =
• What happened?
Carbocation Rearrangement
• Carbocation intermediates can rearrange to form a more
stable carbocation structure
• Hydride shift = H:- moves from C adjacent to carbocation
Carbocation Rearrangement
• Alkyl groups can also shift
• Typically methyl or phenyl
(Major product)
Anti-Markovnikov Addition of HBr
• In the presence of peroxides
• H2O2 or R2O2
• Free radical mechanism
• Only HBr, not HCl or HI
Addition of Halogens
• X2 = Br2 or Cl2 (F2 too reactive, I2 unreactive)
• Solvent = inert, nonaqueous
• Stereochemistry = anti addition
• Two X atoms add from opposite sides of the C=C
• Product = a vicinal dihalide
• Two X atoms on adjacent carbons
Addition of Halogens
• Draw the major product of the following reaction.
Addition of Halogens in the
Presence of Water
• Stereochemistry: X and OH add anti
• Regiochemistry: X adds to the less substituted carbon
OH adds to the more substituted carbon
• Mechanism the same as addition of X2, except H2O is the
nucleophile in the second step
• Water attacks the carbon with the largest d+
• Results in OH on more substituted carbon
• Draw the major product of the following reaction.
• Addition of water
• Three methods:
A. Acid-catalyzed hydration
B. Oxymercuration-demercuration
C. Hydroboration-oxidation
A. Acid-catalyzed hydration
• Regiochemistry = Markovnikov
• Acid catalyst typically H2SO4 or H3PO4 (or just H3O+)
• Carbocation intermediate, so rearrangement can occur
• Draw the major product of the following reaction.
B. Oxymercuration-demercuration
• Step 1: Alkene reacts with mercuric acetate
• Step 2: Reduction with sodium borohydride
• Regiochemistry =Markovnikov
• Stereochemistry = anti addition of OH and H
• No rearrangements
• Milder conditions than H3O+
• Electrophile is +HgOAc
• Formed by dissociation of AcO-Hg-Oac
• Intermediate is bridged mercurinium ion (similar to bromonium)
• Draw the major product for each of the following reactions.
C. Hydroboration-oxidation
• Anti-Markovnikov product
• Syn addition of H and OH (add on same side of C=C)
• No rearrangements
• THF stabilize highly reactive BH3
• Mechanism of first step:
• BH2 on the right because less steric hindrance
• Leads to anti-Markovnikov product
• Second step: H2O2/NaOH replace –BH2 with –OH
• Keep same stereochemistry (syn)
• Draw the major product of the following reaction.
• Draw the major product formed when the following alkene
undergoes (a) acid-catalyzed hydration, (b) oxymercurationdemercuration, and (c) hydroboration-oxidation.
Oxidation and Reduction
• What is oxidation?
• What is reduction?
• Classify these reactions as oxidation or reduction:
• CH3─CH═CH2 → CH3─CH2─CH3
• CH3─CH2─OH → CH3─CO2H
III. Reduction
• Catalytic hydrogenation
• Seen before with heat of hydrogenation (alkene stability)
• Catalyst = metal, usually Pd, Pt, or Ni
• Reaction takes place on metal surface
• Stereochemistry = syn (both H’s add to same side of C=C)
Catalytic Hydrogenation
• This reduction does not work with C=O, C=N, or benzene
except at very high P or T, or with a special catalyst
IV. Oxidation
• Three types
A. Epoxidation
B. Hydroxylation
C. Oxidative cleavage
A. Epoxidation
• Formation of epoxide
• Cyclic ether
• Example:
• Reagent is peroxy acid (RCO3H)
• Stereochemistry = syn
• Another method: treat halohydrin with base:
B. Hydroxylation
• Formation of a 1,2-diol/glycol/vicinal diol
• Methods:
1. Opening of epoxide using aqueous acid
• Product is trans diol
• Mechanism:
2. Addition of osmium tetroxide (OsO4) or potassium
permanganate (KMnO4)
• How do you know these are both oxidizing agents?
• Reaction includes some appropriate work-up
• H2O2 or NaHSO3, H2O for OsO4
• HO- (aq) for KMnO4
• Stereochemistry = syn
• Draw the major product of the following reaction.
C. Oxidative Cleavage
• Oxidize and alkene and split the C=C
• Results in formation of 2 carbonyls
• Type of carbonyls depends on alkene structure and the oxidizing
agent used
• Three types of oxidizing agents
1. Ozone
2. Potassium permanganate
3. Periodic acid
Oxidative Cleavage
1. Ozone
• Ozonolysis
• Reagents: 1. O3
2. (CH3)2S or Zn, H3O+
• Products = 2 carbonyls (ketones or aldehydes)
• Terminal alkenes give CO2
Oxidative Cleavage
2. KMnO4
• Reagents: KMnO4 (excess or concentrated) and heat or acid
• Use heat and excess KMnO4 to split intermediate glycol
• Products = 2 carbonyls (ketones or carboxylic acids)
• Aldehydes oxidize to carboxylic acids in KMnO4
• Terminal alkenes still give CO2
Oxidative Cleavage
2. HIO4
• Specifically used to split glycol
• Draw the major product for each of the following reactions.
V. Polymerization
• Polymer = large molecule synthesized by covalently
linking single parts (monomers)
• Biological polymers: proteins, cellulose, nucleic acids
• Organic polymers: plastics
• Chain-growth polymers: made from alkene monomers
• Radical reaction
Chain-growth Polymerization
• Initiation by peroxides:
• Propagation:
• Termination:
R─CH2CH2• + •CH2CH2─R →
Chain-growth Polymers
• Draw the structure of poly(vinyl chloride).