Alcohols, Ethers & Thiols Singly Bonded Oxygen

Alcohols Structure Alcohols contain a hydroxyl group (-OH) Oxygen is sp3 hybridized, with bent geometry OH bond is polar, so smaller alcohols are soluble in water 1º, 2º, 3º Alcohols

Alcohols

Alcohol Nomenclature Suffix –ol Gets numbering priority over double bonds Hydroxyl carbon must be numbered (C3 or higher)

Nomenclature & Physical Properties High boiling compared to similar MW alkanes due to hydrogen bonding Higher MW alcohols have higher MP/BP

Physical Properties & Reactions C1-C3 alcohols miscible with water Reactions of alcohols Acid catalyzed dehydration to alkenes

Reactions Ease of dehydration: 3º>2º>1º Mechanism – ionic Water is a good “leaving group”

Reactions Orientation of elimination: Zaitsev’s Rule Elimination will predominately give the most substituted alkene

Reactions Oxidation to aldehydes and ketones During double bond formation both carbons have a partial + charge Oxidation to aldehydes and ketones Primary alcohols are oxidized to aldehydes Secondary alcohols are oxidized to ketones

Reactions Rxn w/ acids esters

Ethers Structure – contain C-O-C group – bent geometry like water Nomenclature Common names almost always used Name both groups attached to oxygen, and end both names in –yl

ethoxyethane (diethyl ether) Ethers Common usage – groups ranked in size order IUPAC – OR is named as an alkoxy group CH3CH2OCH2CH3 ethoxyethane (diethyl ether) Physical properties – lower BP, less solubility in water than isomeric alcohols – no H bonding Ethers are relatively inert

Williamson ether synthesis

Thiol structure and nomenclature Contain sulfydryl group (-SH) They are sulfur analogs of alcohols Sulfur is sp3 hybridized, with S-H bond angles of about 100º (big lone pairs) Nomenclature Suffix is –thiol. The “e” of the parent carbon chain is not dropped.

Thiol nomenclature Older name – “mercaptan” CH3SH methyl mercaptan

Thiol reactions Precipitation with mercury salts 2CH3SH + Hg+2  (CH3S)2Hg Oxidation to disulfides