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Alcohols

Alcohols. Contain a hydroxyl (-OH) group. −. +. Intermolecular forces: dipole-dipole, H-bonding 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. + Strong acid.

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Alcohols

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  1. Alcohols • Contain a hydroxyl (-OH) group − + • Intermolecular forces: dipole-dipole, H-bonding • 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 + Strong acid + Strong base alkoxide alcohol oxonium ion

  2. 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) 1,2-ethanediol (ethylene glycol) antifreeze 5-methyl-3-hexanol

  3. Alcohol Naming Practice 2-propanol (isopropyl alcohol) 2,4-dimethyl-3-pentanol 3,5-dimethyl-2,4-heptanediol 4-penten-2-ol

  4. Classes of Alcohols Primary (1°) alcohol 1-butanol OH C attached to 1 other C Secondary (2°) alcohol OH C attached to 2 other C’s 4-phenyl-2-hexanol Tertiary (3°) alcohol OH C attached to 3 other C’s 1-methylcyclohexanol

  5. Reactions of Alcohols Strong base • Reaction with strong bases • alcohol as proton donor (weak acid) • Reaction with strong acids • alcohol as proton acceptor (weak base) • Dehydration • reverse of hydration of alkenes • requires H+ catalyst • Oxidation • increase # of C-O bonds alkoxide Strong acid oxonium ion H+ - H2O alkene oxidizing agent or aldehyde ketone

  6. Dehydration Mechanism Step 1: electrophilic H+ catalyst attacks nucleophilic O atom Step 2: H2O dissociates, leaving behind a carbocation H2O + Step 3: Electrons from neighboring C-H bond form  bond, regenerating H+ catalyst +

  7. Hydration and Dehydration H+ H2O + 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)

  8. Possible Dehydration Products H+ ? The most-substituted alkene product is favored (most stable) Major product Least H’s on double bond

  9. 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 -2 -2 -2 -1 oxidizing agent oxidizing agent 0 +1 +3 +1 -2 0 0 +1 +1 +1 aldehyde carboxylic acid CrO3 (Cr6+) Cr3+

  10. Breathalyzer Tests oxidized oxidized ethanol ethanal (acetaldehyde) ethanoic acid (acetic acid) + Cr6+ + Cr3+

  11. Breathalyzer Tests oxidized oxidized ethanol ethanal (acetaldehyde) ethanoic acid (acetic acid) + Cr6+ + Cr3+ oxidized oxidized methanol methanal (formaldehyde) methanoic acid (formic acid)

  12. Oxidation of Alcohols 0 -2 +1 0 oxidizing agent 2° alcohol 0 +2 -2 0 0 +1 ketone propanone (acetone) 2-propanol oxidizing agent No reaction 3° alcohol

  13. Naming aldehydes and ketones Parent chain = longest chain containing C=O (carbonyl) Aldehyde Ketone oxo –e becomes –al C=O is always C #1 (don’t have to number it) oxo –e becomes –one C=O is lowest possible number (must number it) Prefix Suffix Numbering Naming Priority: Aldehydes > Ketones > Alcohols -OH (alcohol) substituent → “hydroxy” 3-hydroxy-4-methylpentanal 3-chloro-2-butanone

  14. Naming Practice propanedial 2,4-pentanedione Aldehyde has priority Ketone = oxo Has both an aldehyde and a ketone 3-oxopentanal

  15. Condensation of Alcohols Condensation reaction: two molecules combine to form a larger molecule (+ water) • Catalyzed by acid (H+) H2SO4 catalyst + CH3−O−CH3 + H2O CH3−OH H-O−CH3 alcohol alcohol + ether + water

  16. Ethers • 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 H-bond acceptor No H-bond donor − water alcohol Two alkyl groups (C’s) bound to oxygen

  17. Naming Ethers • Common names: name both R groups, add “ether” diethyl ether (anesthetic) ethyl ethyl

  18. Naming Ethers • Common names: name both R groups, add “ether” diethyl ether (anesthetic) ethyl ethyl tert-butyl methyl ether (used as gasoline additive) tert-butyl methyl propyl people ether propyl ♫ “one-eyed, one-horned, flying...” ♪

  19. Reactions of Ethers • Reactions of peroxides: • Formation of peroxides peroxide + O2 diisopropyl ether Explosive! diisopropyl ether peroxide Controlled detonation Resulting crater: 3 feet wide, one foot deep

  20. Aldehydes and Ketones • C=O group called a carbonyl group C and O both sp2 hybridized 120° 120° aldehyde ketone − • Very polar C=O bond • Higher boiling point than alkanes • H-bond acceptor • Soluble in polar solvents • No H-bond donor • Lower boiling point than alcohols +

  21. 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?

  22. C4H10O Isomers 1-butanol 2-butanol 2-methyl-2-propanol 2-methyl-1-propanol diethyl ether methyl propyl ether isopropyl methyl ether

  23. C5H12OIsomers 2-pentanol 1-pentanol 3-pentanol 2-methyl-1-butanol 3-methyl-1-butanol 3-methyl-2-butanol 2,2-dimethyl-1-propanol 2-methyl-2-butanol

  24. C5H12OIsomers sec-butyl methyl ether tert-butyl methyl ether butyl methyl ether isobutyl methyl ether ethyl propyl ether ethyl isopropyl ether

  25. C4H8O Isomers butanal 2-butanone 2-methylpropanal

  26. C5H10O Isomers pentanal 2-pentanone 3-pentanone 3-methyl-2-butanone 3-methylbutanal 2-methylbutanal 2,2-dimethylpropanal

  27. 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 LiAlH4 propanal 1-propanol CH3−CH2−CH2−OH CH3−CH2−CHO NaBH4 2-methyl-3-pentanol 2-methyl-3-pentanone

  28. Reduction of Aldehydes/Ketones LiAlH4 3-oxopentanal 1,3-pentanediol NaBH4 cyclohexanol cyclohexanone H2/Pt pentanedial 1,5-pentanediol

  29. Carboxylic Acid Nomenclature • Parent chain: longest containing carboxyl group (COOH) • Name of parent: replace “–e” with “–oic acid” • Numbering starts at carboxyl carbon • Priority: Carboxylic acid > aldehydes > ketones > alcohols  “hydroxy” substituent “oxo” substituents 3-oxobutanoic acid (diabetes) trans-3-methyl-2-hexenoic acid (human armpits) propanedioic acid (apples)

  30. aspirin Tylenol Can irritate your stomach Gentle on the stomach A carboxylic acid Just an alcohol

  31. Carboxylic Acid Reactions • Reduction to 1° alcohols • Only LiAlH4 reduces carboxylic acids • (not NaBH4 or H2/Pt) LiAlH4 butanoic acid 1-butanol NaBH4 butanoic acid NO RXN or H2/Pt Reactant remains unchanged

  32. What are the products? 3-oxo-4-pentenoic acid H2/Pt NaBH4 LiAlH4 3-hydroxypentanoic acid 3-hydroxy-4-pentenoic acid 4-pentene-1,3-diol

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