alcohol

• Alcohol


  A compound that contains an -OH (hydroxyl group) bonded to a tetrahedral carbon
• Methanol


  The simplest alcohol, CH3OH
• Nomenclature for alcohols


  1. Select the longest carbon chain that contains the -OH group as the parent alkane and number it from the end that gives the -OH the lower number

  2. Change the ending of the parent alkane from -e to -ol and use a number to show the location of the -OH group; for cyclic alcohols, the carbon bearing the -OH group is carbon-1

  3. Name and number substituents and list them in alphabetical order

  
• Alcohols

  • 2-methylpropan-2-ol
  • 2-methylbutan-2-ol
  • 3-methylpentan-2-ol
  • 2,2-dimethylpropan-1-ol

  
• Diol

  A compound containing two hydroxyl groups
• Triol

  A compound containing three hydroxyl groups
• Glycols


  Compounds containing two hydroxyl groups on adjacent carbons
• Alcohols


  • The C-O and O-H bonds are both polar covalent
  • In the liquid state, alcohols associate by hydrogen bonding
• Alcohols have about the same pKa values as water
• Aqueous solutions of alcohols have the same pH as that of pure water
• Phenols


  Weak acids that react with NaOH and other strong bases to form water-soluble salts
• Alcohols


  Weaker acids than phenols and do not react with strong bases in the same way
• Dehydration of alcohols


  1. Elimination of a molecule of water from adjacent carbon atoms gives an alkene

  2. Dehydration is most often brought about by heating an alcohol with either 85% H3PO4 or concentrated H2SO4

  3. 1° alcohols are the most difficult to dehydrate and require temperatures as high as 180°C

  4. 2° alcohols undergo acid-catalyzed dehydration at somewhat lower temperatures

  5. 3° alcohols generally undergo acid-catalyzed dehydration at temperatures only slightly above room temperature
• When isomeric alkenes are obtained, the alkene having the greater number of alkyl groups on the double bond generally predominates
• Dehydration-Hydration


  1. Acid-catalyzed hydration of alkenes to give alcohols and acid-catalyzed dehydration of alcohols to give alkenes are competing reactions

  2. The following acid-catalyzed equilibrium exists

  3. In accordance with Le Chatelier's principle, large amounts of water favor alcohol formation, whereas removal of water from the equilibrium mixture favors alkene formation
• Oxidation of 1° alcohols


  1. Oxidation of a 1° alcohol gives an aldehyde or a carboxylic acid, depending on the experimental conditions

  2. Oxidation of a 1° alcohol to a carboxylic acid is commonly carried out using potassium dichromate, K2Cr2O7, in aqueous sulfuric acid

  3. It is sometimes possible to stop the oxidation at the aldehyde stage by distilling the mixture; the aldehyde usually has a lower boiling point than either the 1° alcohol or the carboxylic acid
• Oxidation of 2° alcohols


  Oxidation of a 2° alcohol gives a ketone
• Tertiary alcohols are resistant to oxidation. In the presence of an acid-catalyst they are prone to dehydration
• Ether


  The functional group of an ether is an oxygen atom bonded to two carbon atoms
• Dimethyl ether


  The simplest ether
• Diethyl ether


  The most common ether
• Nomenclature for ethers


  1. Common names are derived by listing the alkyl groups bonded to oxygen in alphabetical order and adding the word "ether"

  2. Alternatively, name one of the groups on oxygen as an alkoxy group

  
• Cyclic ether


  An ether in which one of the atoms in a ring is oxygen
• Cyclic ethers


  • Ethylene oxide
  • Tetrahydrofuran
• Ethers


  • Polar molecules in which oxygen bears a partial negative charge and each carbon bonded to it bears a partial positive charge
  • Only weak forces of attraction exist between ether molecules in the pure liquid
  • Boiling points of ethers are close to those of hydrocarbons of similar molecular weight
  • Ethers have lower boiling points than alcohols of the same molecular formula
• Ethers resemble hydrocarbons in their resistance to chemical reaction

  
• Ethers do not react with oxidizing agents such as potassium dichromate
• Ethers do not react with reducing agents such as H2 in the presence of a transition metal catalyst or with hydride reducing agents such as NaBH4
• Ethers are not affected by most acids or bases at moderate temperatures
• Because of their general inertness and good solvent properties, ethers, such as diethyl ether and THF, are excellent solvents in which to carry out organic reactions
• Thiol


  A compound containing an -SH (sulfhydryl group)
• The most outstanding property of low-molecular-weight thiols is their stench
• The scent of skunks is due primarily to these two thiols
• Nomenclature for thiols


  1. IUPAC names are derived in the same manner as are the names of alcohols, but the final -e of the parent alkane is retained and the suffix -thiol added

  2. Common names for simple thiols are derived by naming the alkyl group bonded to -SH and adding the word "mercaptan"

  
• Thiols


  • Because of the small difference in electronegativity between sulfur and hydrogen (2.5 - 2.1 = 0.4), an S-H bond is nonpolar covalent
  • Thiols show little association by hydrogen bonding
  • Thiols have lower boiling points and are less soluble in water and other polar solvents than alcohols of similar molecular weight
• Acidity of thiols

  • Thiols are weak acids (pKa 10) and are comparable in strength to phenols (pKa 10)
  • Thiols react with strong bases such as NaOH to form water-soluble thiolate salts
• Oxidation of thiols


  1. The most common reaction of thiols in biological systems is their oxidation to disulfides, the functional group of which is a disulfide (-S-S-) bond

  2. Thiols are readily oxidized to disulfides by O2

  3. Thiols must be protected from contact with air during storage

  4. Disulfides, in turn, are easily reduced to thiols by several reducing agents including H2 in the presence of a transition metal catalyst
• Important alcohols


  • Ethanol
  • Isopropanol
  • Glycerol
  • Ethylene glycol

  
• Propene is the raw material base for the manufacture of these important alcohols