Addition Reactions

general features of addition reactions

2Xs added across pi bond or X & Y are added arcoss pi bonds

Syn addition

add at same time so on the same side

Anti addition

add at different times through bridged intermediate so on different sides

Random Additionally

add at different times, carbocation/carbon radical intermediate forms; can have same side or different sides

syn additions result in (stereochemistry)

enantiomers (mirror images) → 50:50 racemic mixture

anti addition results in (stereochemistry)

identical; only mesocompound bc achiral, internal mirror plane, & 2 chiral centers

Hydrohalogenation

adding H and halogen to C=C

Hydrohalogenation produces

Markovnikov product (major) and Anti-Markovnikov products (minor)

Markovnikov’s Rule

When H-A is added to a C=C, the H⁺ adds to the least substituted carbon so a more stable carbocation can form

Hydrohalogenation using just H-X

produce Markovnikov as major product and anti-Markovnikov as minor product; all heterolytic cleavages & H bonds first & carbocation intermediates

Hydrohalogenation with H-X and H₂O₂

gets Anti-Markovnikov as major product and Markovnikov as minor product; uses homolytic cleavage & carbon radical intermediates & Br binds first

Which halogenation (H-X or H-X & H₂O₂) gets markovnikov as major product?

with H-X

Which halogenation (H-X or H-X & H₂O₂) gets markovnikov as minor product?

H-X and H₂O₂

Hydration with acid-catalyzed

Markovnikov product is major; rearrangement; regenerates acid so only a small amount is needed; heterolytic cleaves & H bonds first & carbocation forms

Hydration with Acid-catalyzed mechanism

heterolytic cleavage; H bonds first, then OH₂, then hydrogen is removed by H₂O to get OH on compound

Common acids for acid-catalyzed hydration

H₂SO₄ & H₃PO₄

Oxymercuration-Demercuration Hydration

adds and removes mercury to get OH and H on compound; anti-addition & favors Markovnikov product; no rearrangment; heterolytic cleavages & forms bridged intermediates

Oxymercuration mechanism

bridged intermediate; H₂O attacks carbon that is more substituted & anti-addition

Demercuration mechanism

just know this; favors Markovnikov product & no rearrangement

Hydroboration-Oxidation

favors Markovnikov; gets product with OH and H on compound; two steps

Hydroboration-Oxidation Mechanism

favors anti-Markovnikov; all heterolytic cleavages & syn addition & H bonds to the more substituted carbon because of sterics; no rearrangment

Types of Hydrohalogenation

use H-X or use H-X and H₂O₂

Types of Hydration

Acid-Catalyzed, Oxymercuration-Demercuration, Hydroboration-Oxidation

Which hydration methods favor Markovnikov products?

acid-catalyzed, Oxymercuration-Demercuration

Which hydration methods favor anti-Markovnikov products?

Hydroboration-Oxidation

Side of Addition (Stereoselectivity) of Acid-Catalyzed Hydration

random bc C⁺ intermediate; 50:50 racemic mixture

Side of Addition (Stereoselectivity) of Oxymercuration-Demercuration

anti bc stepwise

Side of Addition (Stereoselectivity) of Hydroboration-Oxidation

syn bc concerted

Rearrangment in hydration?

only in acid-catalyzed hydrations

Acid-Catalyzed reagents

H₂0, H⁺_catylase

Oxymercuration-Demercuration reagents

1) Hg(OAc)₂, H₂O; 2) NaBH₄

Hydroboration-Oxidation reagents

1) BH₃; 2) NaOH, H₂O₂

Acid-Catalyzed regioselectivity

markovnikov

Oxymercuration-Demercuration regioselectivity

markovnikov

Hydroboration-Oxidation regioselectivity

anti-markovnikov

Alkene → Ether

acid-catalyzed or oxymercuration-demercuration; like hydration but with ROH; get H and OR

Alkene → ether acid-catalyzed method mechanism

OR on more substituted carbon; add H and OR

common acids for alkene → ether with acid-catalyzed

H₂SO₄, H₃PO₄

Alkene → ether with acid-catalyzed method reagents

ROH, HA

Alkene → ether with acid-catalyzed method regioselectivity

Markovnikov

Alkene → ether with acid-catalyzed method side of addition (stereoselectivity)

random; 50:50 mixture

Alkene → ether with acid-catalyzed method rearrangment

yes

Alkene → ether with oxymercuration-demercuration method mechanism

get RO and H in place of double bond; like hydration but with OR

Alkene → ether with oxymercuration-demercuration method reagents

1) Hg(OAc)₂, ROH; 2) NaBH₄

Alkene → ether with oxymercuration-demercuration method regioselectivityq

stepwise/anti

Alkene → ether with oxymercuration-demercuration method rearrangement

no

Alkene → Di-Halogen

replace double bond with two hydrogens; meso and racemic mixture products with meso predicted in lab

Alkene → di-Halogen mechanism for meso

anti-addition; similar to intermediate in oxymercuration-demercuration and S_N2

What does free radical halogenation target?

sp³ C-H; with heat and light

What does alkene → di-halogen target?

double bond

What are other common non-X₂ halogenation reagents?

Alkene → Di-Halogen reagents

X₂ or common non-X₂

Alkene→Di-Halogen side of addition (stereoselectivity)

anti or syn

Alkene → Di-Halogen rearrangement

no

Alkene → Alcohol + Halogen

halohydrin

Halohydrin

X (Br, Cl, or I) and OH replace double bond

Halohydrin mechanism

anti-addition with the nucleophile attacking the more substituted carbon; bottom and top attacks; same first step as di-halogen

Stronger nucleophile: Br^- or H₂O

H₂O

Where do nucleophiles attack?

more substituted carbon

Halohydrin reagents

X₂ (Cl, Br, I) and H₂O

Halohydrin side of addition (stereoselectivity)

anti-addition bc stepwise

Halohydrin rearrangement

no

Alkene → Alkane

hydrogenation

Hydrogenation

two hydrogens replace double bond

Hydrogenation mechanism

diastereomer products

Hydrogenation reagents

H-H, metal catalyst (Pt, Pd, Ni)

Hydrogenation side of addition (stereoselectivity)

syn-addition

Hydrogenation rearrangement

no