Unit 5: Alkyl Halides and Alcohols - Vocabulary

Vocabulary flashcards covering SN1/SN2, E1/E2/E1cB, carbocation chemistry, hydration, reduction and Grignard reactions, dehydration, ether formation, and alcohol oxidation.

Nucleophile

A species that donates an electron pair to an electrophile during a reaction; often bears a negative charge or lone pairs (e.g., OH−).

Electrophile

An electron-poor species that accepts an electron pair from a nucleophile; in alkyl halides, the carbon bearing the leaving group is electrophilic.

Leaving group

The group that departs with its bonding electrons in a substitution or elimination reaction; good leaving groups form stable anions.

SN1

Nucleophilic substitution with unimolecular rate-determining step that forms a carbocation; common with tertiary substrates; can lead to racemization.

SN2

Bimolecular nucleophilic substitution with backside attack; transition state; inversion of configuration at the reacting carbon; rate depends on both nucleophile and substrate.

E1

Elimination via unimolecular mechanism: leaving group leaves to form a carbocation, then base removes a proton to form an alkene.

E2

Elimination via a concerted mechanism: base abstracts a proton as the leaving group leaves; alkene forms in one step; rate depends on base and substrate.

E1cB

Elimination via a carbanion intermediate formed by deprotonation before leaving group departure; then leaving group leaves to form the alkene.

Carbocation

A positively charged carbon intermediate formed during SN1 and E1 reactions; typically planar and can lead to racemization.

Transition state

High-energy arrangement during bond rearrangement as reactants convert to products; features partial bonds.

Inversion (SN2)

Opposite stereochemistry at the reacting carbon resulting from backside attack in an SN2 reaction.

Racemization (SN1)

Loss of optical activity due to the planar carbocation allowing attack from both faces, yielding enantiomeric products.

Zaitsev's rule

In elimination, the more substituted alkene is the major (favored) product.

Hydration (alkenes)

Addition of water across a carbon–carbon double bond to form an alcohol, usually acid-catalyzed.

Reduction

Conversion of carbonyl compounds or other groups to a lower oxidation state (e.g., to alcohols).

Reducing agent

A reagent that donates hydride or electrons to reduce substrates (e.g., NaBH4, LiAlH4).

Sodium borohydride (NaBH4)

A mild reducing agent that reduces aldehydes and ketones to alcohols; typically used with aqueous workup.

Lithium aluminum hydride (LiAlH4)

A strong reducing agent that reduces aldehydes, ketones, carboxylic acids, and esters to alcohols; used in ether solvent.

Grignard reagent

An organomagnesium halide prepared from organohalides and Mg; reacts with carbonyl compounds to form alcohols after workup.

Formaldehyde with Grignard (primary alcohol)

Grignard reagent reaction with formaldehyde yields a primary alcohol after acidic workup.

Aldehydes with Grignard reagents

Grignard adds to aldehydes to form secondary alcohols after workup.

Ketones with Grignard reagents

Grignard adds to ketones to form tertiary alcohols after workup.

Williamson ether synthesis

Synthesis of ethers by reacting an alkoxide with a primary alkyl halide in an SN2 mechanism.

Alkoxide

Conjugate base of an alcohol formed by deprotonation; used to generate ethers in Williamson synthesis.

Protonation of alcohol (dehydration mechanism)

Protonation of the alcohol oxygen to form a better leaving group (protonated alcohol) prior to carbocation formation.

Carbocation formation (dehydration)

Loss of water after protonation to give a carbocation intermediate in dehydration.

Elimination dehydration mechanism (E1)

Two-step process: protonation, carbocation formation, then loss of a proton to form an alkene.

Oxidation of alcohols (oxidizing agents)

Conversion of alcohols to higher oxidation state products using oxidants such as CrO3, Na2Cr2O7, or periodinane.

Chromium trioxide (CrO3)

A strong oxidizing agent used to oxidize primary and secondary alcohols.

Sodium dichromate (Na2Cr2O7)

A strong oxidizing agent used in oxidation of alcohols to carbonyls.

Periodinane

A mild, versatile oxidizing agent used for selective oxidation of alcohols (e.g., Dess–Martin periodinane).