Alkene Reactions, Section 2

Radical Halide Addition Reaction of Alkenes with HBr (with radical formation). Reaction Type: Radical Addition; 1 reduced (H) and 1 oxidized (X) Overall Reaction: HBr + alkenes  Hydrogen Halide Reactivity Order: Regioselectivity: ____Markovnikov (goes through most stable free radical intermediate). C H 3 2 C H 3 2 B r h u 2

Radical Halide Addition Reaction of Alkenes with HBr (with radical formation). Stereoselectivity: Mechanism includes a planar free-radical. Requirements. ___________________initiate radical reaction via: RO + HBr  ROH + Br 2

Radical Halide Addition Mechanism: H C 2 3 B r H C 2 3 B r H B r H H B r C H H 3 2

Non-Radical vs. Radical Addition Conditions Electrophile Intermediate Regioselectivity 2

Overall Reaction: Alkenes + Acids  Hydration Reaction Type: Overall Reaction: Alkenes + Acids  Regioselectivity: _______Markovnikov’s Rule (_______________intermediate). Stereoselectivity: Requirements: Aqueous acid (usually H2SO4). . 2

Hydration H C 3 + 2 O H C 3 H C 3 H H C H H 3 _________________act as Lewis Base, _____ is electrophile, water acts as ___________. 2

Follows Markovnikov's Rule 50% H2SO4 50% H2O CH2 4

Suppose you wanted to prepare 1-decanol from 1-decene? Synthesis Suppose you wanted to prepare 1-decanol from 1-decene? OH Needed: a method for hydration of alkenes with a regioselectivity ___________ Markovnikov's rule. 13

Hydroboration Oxidation Reaction Type: Overall Reaction: Alkenes  Regioselectivity: ______Markovnikov’s Rule Stereoselectivity:. Requirements: – Electrophilic Addition – Oxidation 2

Hydroboration Oxidation C 2 3 B t R e p a 2 x H C 2 3 B R H C 3 B H 2 H O - H C 2 3 B R O _ H C 2 3 O B R _ + O H H C 2 3 O - H C 2 3 O H O R e p a t c y l 2 + B R 2 O H 2

Hydroboration Oxidation Step 1: H C 2 3 B H C 3 B H 2 2

Hydroboration Oxidation Step 2: t R e p a 2 x H C 2 3 B H C 2 3 B R 2

Hydroboration Oxidation Step 3: H C 2 3 B R O _ H C 2 3 B R H O - 2

Hydroboration Oxidation Step 4: H H C 2 3 O B R H C C H C H 2 3 _ B R 2 H O O 2

Hydroboration Oxidation Step 5: H C 2 3 O B R H C 2 3 O - _ + O H + B R 2 O H 2

Hydroboration Oxidation Step 6: H C 2 3 O - H C 2 3 O H O 2

Overall Reaction: Alkene  Regioselectivity: ___Markovnikov’s Rule Halogenation Reaction Type: Overall Reaction: Alkene  Regioselectivity: ___Markovnikov’s Rule (_______ acts as electrophile). Reactivity Order: Stereoselectivity: Requirements: 2

Mechanism: Reaction proceeds via _________ __________ ion. Halogenation Mechanism: Reaction proceeds via _________ __________ ion. B r B r B r - B r 2

Formation of Bromonium Ion 11

Example Br2 CH3CH CHCH(CH3)2 CHCl3 0°C 4

Overall Reaction: Alkene  vicinal Regioselectivity: Halohydration Reaction Type: Overall Reaction: Alkene  vicinal Regioselectivity: Stereoselectivity: Requirements: X2/H2O or HOX (hypohalous acid). 2

Halohydration Mechanism: B r O B r O B r H + 3 H 2 O B r Br H 2 O 2

Examples H2O H2C CH2 + Br2 OH Cl2 H H2O 6

Regioselectivity CH3 OH C CH2Br H3C C CH2 Br2 H2O (77%) Markovnikov's rule applied to halohydrin formation: the halogen adds to the carbon having the ____________ number of hydrogens. 32

are examples of heterocyclic compounds Epoxides are examples of heterocyclic compounds three-membered rings that contain oxygen H2C CH2 O H2C CHCH3 O 2

Overall Reaction: Alkene  Regioselectivity: Stereoselectivity: Epoxidation Reaction Type: Overall Reaction: Alkene  Regioselectivity: Stereoselectivity: Requirements: 2

Epoxidation Mechanism: - O R + H d H O - d + d + O d R O 2

Example + CH3COOH O + CH3COH O 7

Overall Reaction: Alkene  Ozonolysis Reaction Type: Overall Reaction: Alkene  Requirements: Ozone, Reductive work up (Zn in acetic acid; HC2H3O2). 2

Epoxidation Mechanism: + _ O O O " R ' H O H R " R ' R R " ' C H O + R 2nd C-O is formed by nucleophilic O attacking other end of C=C Mechanism: + _ O O O Step 1: Pi bond acts as nucleophile, attacks O3 on electrophilic terminal O. " R ' H O Step 2: Cyclic ozonide rearranges to the malozonide. H R " R ' R R " ' C H O + R " ' C O H Step 3: Work up. Zn/acetic acid makes malozonide decompose to two carbonyl groups. 2

Example CH3 CH2CH3 H C 1. O3 2. H2O, Zn 19