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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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