Alcohols • Homer Simpson and Organic Chemistry Alcohols H3C O H • Contain a hydroxyl (-OH) group − R O O H3C H H + H • Intermolecular forces: dipole-dipole, H-bonding O H • H-bonds between alcohol molecules: high boiling points • H-bonds with water: up to 4-carbon alcohols soluble in water • -OH group can act as a weak base or a weak acid H R O alkoxide + Strong base R OH alcohol + Strong acid R O oxonium ion H Alcohol Nomenclature • Parent chain = longest chain containing C with -OH • Root name: replace –e with –ol • ethane ethanol, butene butenol, etc. • Give –OH the smallest possible number • –OH has priority over double bonds, alkyl groups • Two –OH groups -diol; three –OH groups -triol – Add to end of root name (propane propanediol) HO OH OH 5-methyl-3-hexanol 1,2-ethanediol (ethylene glycol) antifreeze Alcohol Naming Practice OH OH 2-propanol (isopropyl alcohol) 2,4-dimethyl-3-pentanol OH OH OH 3,5-dimethyl-2,4-heptanediol 4-penten-2-ol Classes of Alcohols OH 1-butanol Primary (1°) alcohol OH C attached to 1 other C OH Secondary (2°) alcohol OH C attached to 2 other C’s 4-phenyl-2-hexanol CH3 OH 1-methylcyclohexanol Tertiary (3°) alcohol OH C attached to 3 other C’s Reactions of Alcohols • Reaction with strong bases R OH Strong base R – alcohol as proton donor (weak acid) • Reaction with strong acids R alkoxide OH H Strong acid R H – reverse of hydration of alkenes H – requires H+ catalyst • Oxidation – increase # of C-O bonds oxonium ion OH C C H H O H – alcohol as proton acceptor (weak base) • Dehydration O CH3 H H+ - H2O CH3 C C H H alkene R OH O oxidizing agent R O or H aldehyde R R' ketone Dehydration Mechanism Step 1: electrophilic H+ catalyst attacks nucleophilic O atom H H H OH C C H H CH3 H H H O H C C H H CH3 Step 2: H2O dissociates, leaving behind a carbocation H H H O H C C H H CH3 H H C CH3 C H H + H 2O Step 3: Electrons from neighboring C-H bond form bond, regenerating H+ catalyst H H C H C CH3 H H CH3 C H C + H H Hydration and Dehydration H CH3 C H C H+ + H H 2O H H OH C C H H CH3 Hydration and dehydration are in equilibrium Can change [H2O] to favor one reaction or the other Change Favors Increase [H2O] Formation of Alcohol (hydration) Decrease [H2O] Formation of Alkene (dehydration) Possible Dehydration Products OH H+ ? H OH H OH Least H’s on double bond Major product OH H The most-substituted alkene product is favored (most stable) Oxidation of Alcohols • Oxidation: increases oxidation number – More C-O bonds (add O) or increases bond order – Fewer C-H bonds (remove H) • Needs an oxidizing agent – CrO3, Cr2O72-, MnO4-,or PCC (pyridinium chlorochromate) PCC stops at aldehyde 1° alcohol +1 H 0R -1 -2 -2 C +1 H OH +1 oxidizing agent 0R -2 O C oxidizing agent +1 H +1 aldehyde CrO3 (Cr6+) Cr3+ O +3 C 0R -2 OH +1 carboxylic acid Breathalyzer Tests H oxidized CH3 C OH oxidized CH3 + Cr6+ CH3 C H H ethanol O O C OH ethanal ethanoic acid (acetaldehyde) (acetic acid) + Cr3+ Breathalyzer Tests H oxidized CH3 C OH oxidized CH3 CH3 C ethanol + Cr6+ OH ethanal ethanoic acid (acetaldehyde) (acetic acid) + Cr3+ H C C H H H O O O O OH H methanol oxidized H oxidized C H H C OH methanal methanoic acid (formaldehyde) (formic acid) Oxidation of Alcohols 0 2° alcohol 0 0 R R -2 +1 C OH oxidizing agent -2 +1 H +2 0R O C R0 ketone H CH3 O C CH3 OH C CH3 CH3 propanone 2-propanol (acetone) R 3° alcohol R C R OH oxidizing agent No reaction Naming aldehydes and ketones Parent chain = longest chain containing C=O (carbonyl) Aldehyde Ketone oxo oxo Prefix –e becomes –al –e becomes –one Suffix Numbering C=O is always C #1 C=O is lowest possible number (don’t have to number it) (must number it) Naming Priority: Aldehydes > Ketones > Alcohols -OH (alcohol) substituent → “hydroxy” OH O O Cl H 3-hydroxy-4-methylpentanal 3-chloro-2-butanone Naming Practice O O O O propanedial Has both an aldehyde and a ketone 2,4-pentanedione O O Aldehyde has priority Ketone = oxo 3-oxopentanal Condensation of Alcohols Condensation reaction: two molecules combine to form a larger molecule (+ water) – Catalyzed by acid (H+) CH3−OH + H-O−CH3 alcohol + alcohol H2SO4 catalyst CH3−O−CH3 + H2O ether + water Ethers H R O O H H − water alcohol R O R H-bond acceptor No H-bond donor Two alkyl groups (C’s) bound to oxygen • Intermolecular forces: – Dipole-dipole – No H-bonding between ether molecules • Lower boiling point than alcohols – Water or alcohols can H-bond to ether oxygen • Somewhat soluble in water and other polar solvents Naming Ethers • Common names: name both R groups, add “ether” O ethyl ethyl diethyl ether (anesthetic) Naming Ethers • Common names: name both R groups, add “ether” diethyl ether (anesthetic) O ethyl ethyl tert-butyl methyl ether (used as gasoline additive) CH3 O tert-butyl methyl O propyl O O propyl people ether ♫ “one-eyed, one-horned, flying...” ♪ Reactions of Ethers • Formation of peroxides peroxide O O + H O2 O O diisopropyl ether • Reactions of peroxides: Explosive! diisopropyl ether peroxide Controlled detonation Resulting crater: 3 feet wide, one foot deep Aldehydes and Ketones O 120° R O C and O both sp2 hybridized C H 120° C R' R aldehyde ketone • C=O group called a carbonyl group − R O O C C + H R Very polar C=O bond • Higher boiling point than alkanes H H-bond acceptor • Soluble in polar solvents No H-bond donor • Lower boiling point than alcohols Structural Isomers • Draw all the possible structural isomers for the following formulas: C4H10O C5H12O C4H8O C5H10O Alcohols and Ethers Aldehydes and Ketones (contain a double bond) Notice that all formulas contain one oxygen What functional groups do you know that contain one oxygen? Does the atom ratio of carbon to hydrogen make a difference? C4H10O Isomers OH OH 1-butanol 2-butanol OH OH 2-methyl-2-propanol O diethyl ether 2-methyl-1-propanol O methyl propyl ether O isopropyl methyl ether C5H12O Isomers OH OH OH 2-pentanol 1-pentanol 3-pentanol OH HO OH 2-methyl-1-butanol 3-methyl-2-butanol OH 2-methyl-2-butanol 3-methyl-1-butanol OH 2,2-dimethyl-1-propanol C5H12O Isomers O butyl methyl ether O isobutyl methyl ether O tert-butyl methyl ether O ethyl propyl ether O sec-butyl methyl ether O ethyl isopropyl ether C4H8O Isomers O O butanal 2-butanone O 2-methylpropanal C5H10O Isomers O O O pentanal 2-pentanone 3-pentanone O O 3-methylbutanal O 2,2-dimethylpropanal 3-methyl-2-butanone O 2-methylbutanal Reactions of Aldehydes and Ketones • Oxidation of aldehydes to carboxylic acids – CrO3, MnO4- • Reduction of aldehydes and ketones to alcohols – Decrease C-O bonds, increase C-H bonds – Reducing agents: LiAlH4, NaBH4, H2/Pt O LiAlH4 propanal OH H 1-propanol CH3−CH2−CH2−OH CH3−CH2−CHO O OH NaBH4 2-methyl-3-pentanone 2-methyl-3-pentanol Reduction of Aldehydes/Ketones O OH LiAlH4 OH O 3-oxopentanal 1,3-pentanediol OH O NaBH4 cyclohexanol cyclohexanone O O pentanedial H2/Pt HO 1,5-pentanediol OH Carboxylic Acid Nomenclature O R C • Parent chain: longest containing carboxyl group (COOH) O H • Name of parent: replace “–e” with “–oic acid” • Numbering starts at carboxyl carbon – Priority: Carboxylic acid > aldehydes > ketones > alcohols O O “hydroxy” “oxo” substituent substituents OH 3-oxobutanoic acid O (diabetes) O HO O OH OH propanedioic acid (apples) trans-3-methyl-2-hexenoic acid (human armpits) OH O O OH O HN O CH3 aspirin Tylenol Can irritate your stomach Gentle on the stomach A carboxylic acid Just an alcohol Carboxylic Acid Reactions • Reduction to 1° alcohols – Only LiAlH4 reduces carboxylic acids (not NaBH4 or H2/Pt) O LiAlH4 butanoic acid 1-butanol OH OH butanoic acid O NaBH4 OH or H2/Pt O NO RXN OH Reactant remains unchanged What are the products? O O OH 3-oxo-4-pentenoic acid H2/Pt NaBH4 LiAlH4 OH O OH OH O OH 3-hydroxypentanoic acid 3-hydroxy-4-pentenoic acid OH OH 4-pentene-1,3-diol