ALL redox

Reduction

• Decrease oxidation state

• Gain of C–H bonds

  Loss of C–X bonds or C–O bonds

• Example: alkyne → alkene → alkane

Pd/C + H₂

Hydrogenation (reduction)

What it reduces:

• alkene → alkane

• alkyne → alkane

• aldehyde → alcohol

• ketone → alcohol

Stereochemistry:
syn addition

(two H add same side)

Hydrogenation outcome

Pd/C + H₂

Adds 2 hydrogens across π bond

alkene → alkane

alkyne → alkane

carbonyl → alcohol

Lindlar's Catalyst, H2

Reaction type: partial alkyne reduction

What it reacts with: alkyne

Outcome: alkyne → cis alkene TWO H SAME FACE

Stereochemistry: syn addition

Key: poisoned Pd catalyst, reaction stops at alkene

Na0 / NH₃

Reaction type: dissolving metal reduction

Outcome:

alkyne → trans alkene H ON OPPOSITE

Stereochemistry:

anti addition

(H atoms opposite sides)

Alkyne Reduction Summary

Pd/C + H₂ → alkane

Lindlar + H₂ → cis alkene

Na / NH₃ → trans alkene

LiAlH₄

Lithium aluminum hydride

Reduces:

• alkyl halides R–X (halogen)

• sulfonates (OTs good LG) R–O–SO₂–Ph

Outcome:

C–X → C–H

Hydride H⁻ acts as a nucleophile and performs an SN2 attack. less substituted carbon (because SN2).

LiAlH₄ mechanism type

Behaves like SN2

Hydride (H⁻) attacks carbon

Stereochemistry:

inversion of configuration

(backside attack)

Oxidation

• Increase oxidation state

• More bonds to heteroatoms

• Fewer C–H bonds

Example:

alcohol → aldehyde → carboxylic acid

mCPBA

Reaction: Epoxidation

What it reacts with: Alkene

Outcome: Alkene → epoxide

Stereochemistry:
syn addition (O adds to the same face of the alkene)

• cis alkene → cis epoxide

• trans alkene → trans epoxide

Products: Epoxide + enantiomer (if new stereocenter forms)

O inserts across C=C to form a 3-membered epoxide ring.

Syn dihydroxylation

1. OsO4/ 2. NaHSO3/ H2O
alkene → syn diol

two OH groups add to same side

product:

cis diol

+e

Anti dihydroxylation

1. mCPBA / 2. KOH
alkene → anti diol

two OH groups add to opposite sides

product:

trans diol

+e

Ozonolysis

Ozonolysis ozone (o3) splits the double or triple bond into two molecules.

Reagents:

1. O₃

2. Zn / H₂O or (CH₃)₂S

Outcome:

alkene → two carbonyl compounds

(aldehydes or ketones)

reduction of alkene: hydrogenation

reduction of alkene: hydrogenation

reduction of carbonyl. reduce aldehyde

reduction of carbonyl, reduce ketone

reduction of alkyne

reduction of alkyne, cis alkene

reduction of alkyne, trans alkene

reduction of epoxide

reduction of alkyl halides and sulfonates

reduction of alkyl halides and sulfonates

epoxidation

dihydroxylation

dihydroxylation

oxidative cleavage

oxidative cleavage

oxidation

oxidation

LiAlH₄, H₂O

• epoxide ring opening

• Mechanism: SN2 attack by hydride (H⁻)

• Attack occurs on less substituted carbon

• Outcome: epoxide → alcohol

ring opens

H adds to one carbon

OH forms after H₂O workup

OsO₄, NaHSO₃, H₂O

Reaction type: dihydroxylation

What it reacts with: alkene

Outcome: alkene → syn diol (two OH same face of the double bond)

Stereochemistry: syn addition

mCPBA, KOH

Reaction type: anti dihydroxylation

Steps:

1. epoxide formation

2. base opening

What it reacts with: alkene

Outcome: alkene → anti diol anti diol (two OH opposite sides)

Stereochemistry: anti addition

O₃, Me₂S

Reaction type: ozonolysis

What it reacts with: alkene

Outcome: alkene → 2 NEW aldehydes/ketones

Key: breaks C=C bondIf that alkene carbon had at least one H on it → it becomes an aldehyde

• If that alkene carbon had only carbons attached (no H) → it becomes a ketone

O₃, H₂O

Reaction type: oxidative cleavage

What it reacts with: alkyne

Outcome: alkyne → carboxylic acid

carboxylic acid:containing –COOH , has two parts Carbonyl (C=O), Hydroxyl (–OH) attached to the same C

Key: breaks C≡C bond

PCC

Reaction type: Partial oxidation

What it reacts/STARTS with:

1° alcohol

2° alcohol

Outcome:

1° alcohol → aldehyde

2° alcohol → ketone

Key: Stops at aldehyde (does NOT oxidize to carboxylic acid)

Jones reagent

CrO₃, H₂SO₄, H₂O

Reaction type: strong oxidation

What it reacts with:

1° alcohol
2° alcohol

Outcome:

1° alcohol → carboxylic acid

2° alcohol → ketone

Reduction reagents

Pd/C, H₂ → alkane

Lindlar → cis alkene

Na/NH₃ → trans alkene

LiAlH₄ → strong hydride reduction

Oxidation reagents

mCPBA → epoxide

OsO₄ → syn diol

mCPBA + KOH → anti diol

O₃ + Me₂S → aldehydes / ketones

O₃ + H₂O → carboxylic acids

PCC → aldehyde

Jones → carboxylic acid

Dihydroxylation

alkene → diol

adds two OH groups

two possible stereochemistries:

syn-diol
anti-diol

Pd/C, H₂ for Carbonyls

Carbonyl: C=O (carbon double bonded to oxygen)

Aldehyde: R–CHO, 1 C / 1 H

Ketone: R–CO–R′, 2 C

Outcome:

aldehyde → 1° alcohol

ketone → 2° alcohol

What happens:

gain C–H bond

C=O becomes C–OH

Stereochemistry:

syn addition

H₂SO₄

They dehydrate an alcohol to form an alkene.

ROH→alkene

Think: alcohol → elimination → double bond.

POCl₃ / pyridine

They dehydrate an alcohol to form an alkene.

ROH→alkene

Think: alcohol → elimination → double bond.

H₃PO₄

Strong acid for alcohol dehydration → alkene

For 2°/3° alcohols: usually E1 → carbocation forms, so check for rearrangement.

tsoh

Strong acid for alcohol dehydration → alkene