Organic Chemistry I - Synthesis Reactions

Radical Chlorination of Alkanes Nuc

Cl2, hv

Radical Bromination of Alkanes Nuc

Br2, heat

Radical Fluorination of Alkanes Nuc

F2, hv

SN2 reaction

Nucleophile: Strong, small, negative nuc only

• Examples → I⁻, Br⁻, CN⁻, SH⁻, OR⁻, OH⁻

Solvent: Polar aprotic (no H-bonding)

• DMF, DMSO, acetone

MeX » 1 » 2 Never happens with 3° (too hindered)

SN1 reaction

Nucleophile: Weak

• H₂O, ROH

Solvent: Polar protic (H20, CH3OH)

• stabilizes carbocation; intermediate

• Rearrangements common

3 » 2 » 1 » » methyl

E2 reaction

Nucleophile/Base: Strong Bulky Base

• t-BUO-, LDA, NaOH

Solvent: Polar aprotic (DMSO, acetone)

• No carbocation rearrangement

3 » 2 » 1 primary only if bulky)

• formation of an alkene

E1 reaction

Nucleophile/Base: Weak Base

• H2O, CH3OH, EtOH, NH3, COOH

Requires: Heat + acid

• Rearrangements common

3 » 2 » 1

• formation of an alkene

• Competes with SN1

What does LiAlH₄ reduce?

Carbonyls of ALL types — aldehydes, ketones, esters, acids

What does LiAlH₄ use?

LiAlH4, Et2O and H3O+ for protonation

What does NaBH₄ reduce?

Aldehydes and ketones only

What does a Grignard reagent attack?

Carbonyl carbon, forming a new C–C bond

What does Grignard reactions use?

CH3MgBr and H3o+ for protonation

What does PCC use as its solvent?

CH2Cl2

What does PCC form?

converts an alcohol to ketone/aldehyde

What does PCC do to 1° alcohols?

aldehydes

What does PCC do to 2° alcohols?

ketones

What does chromic acid oxidation do to 1° alcohols?

Oxidizes to carbonyls/carboxylic acids

What does chromic acid oxidation do to 2° alcohols?

Oxidizes to ketones

What does chromic acid oxidation use

K2Cr2O7 (or Na2Cr2O7 or CrO3)

• solvents: H2O, H2SO4 for protonation

What mechanism will a HX have with a primary R-OH?

SN2 mechanism

What mechanism will a HX have with a secondary/tertiary R-OH?

SN1 mechanism

What reagent converts alcohols to alkyl halides?

HCl, HBr, HI

Which reagent converts a 1° or 2° alcohol to a halide via SN2? (PX3)

PBr₃ or PCl₃ or P, I₂

What stereochemical effect does PX₃ substitution have?

Inversion of configuration

Do rearrangements occur with PX₃?

No — SN2 mechanism

What reagents convert OH to a tosylate or mesylate?

TsCl or MsCl + pyridine

Why tosylate formation is useful?

Creates an excellent leaving group without altering stereochemistry

What mechanism does ROTs undergo next?

SN2 or E2

What conditions cause dehydration of alcohols to alkenes?

• (Acid-catalyzed dehydration of Alcohols)

H₂SO₄ + heat

What mechanism is followed?

• E2 for 1° (170-180 C)

E1 for 2°/3° (100-140, 25-80 C)

What major risk occurs in dehydration?

Carbocation rearrangements

What substrates are required for Williamson ether synthesis?

1° alkyl halide + alkoxide ion

Wgat are the solutions used from the Williamson Ether synthesis?

NaH, CH3CH2I

When do rearrangements happen?

Any reaction that forms a carbocation (SN1, E1, dehydration, tertiary alcohol + HX). NEVER in SN2 or E2.