Pharmaceutical Organic Laboratory

• Hydrocarbons


  Organic compounds composed of carbon and hydrogen atoms only
• Hydrocarbons


  • Most are used as fuel (petroleum products) because of their flammable property
  • Have a special property to catenate forming seemingly endless chain of carbons (potential combinations estimated up to 10^6)
  • Are non-polar in nature, thereby most of them are insoluble in water
• Classification of hydrocarbons based on presence of multiple bonds

  • Saturated - carbon atoms are bonded with single bond
  • Unsaturated - carbon atoms are bonded with double or triple bonds
• Single bond


  Possesses one sigma bond which is a relatively strong type of bond compared to double and triple bonds which possess a sigma and pi bonds; pi bonds are relatively weak type of bond
• Unsaturated hydrocarbons are more reactive than saturated ones
• Classification of hydrocarbons based on structure

  • Open-chain - linear structure; could be straight or branched chains
  • Closed-chain - ring structure; could be aliphatic or aromatic
• Aliphatic hydrocarbons


  • Alkanes (saturated, single bonds)
  • Alkenes (unsaturated, double bonds)
  • Alkynes (unsaturated, triple bonds)
  • Cycloalkanes (cyclic, saturated)
  • Cycloalkenes (cyclic, unsaturated)
  • Cycloalkynes (cyclic, unsaturated)
• Aromatic hydrocarbons


  • Benzene and its derivatives
  • Polycyclic benzenoids
• Aliphatic hydrocarbons


  Open-chain hydrocarbons
• Alkanes


  Saturated hydrocarbons with single bonds, also called paraffins
• Alkenes


  Unsaturated hydrocarbons with double bonds, also called olefins
• Alkynes


  Unsaturated hydrocarbons with triple bonds
• Aromatic hydrocarbons


  Cyclic hydrocarbons with delocalized pi electrons between carbon atoms of ring
• Criteria for aromaticity


  • Must be cyclic in structure
  • Must be flat or planar in configuration
  • Must have conjugated double bonds
  • Must follow Hückel's rule of aromaticity
• Hückel's rule of aromaticity

  A compound is particularly stable if all of its bonding molecular orbitals are filled with paired electrons, where the number of pi electrons = 4n + 2 = n, where n = 0 or any positive whole integer
• Benzene, being the most common example of an aromatic compound, generally undergoes electrophilic aromatic substitution reactions
• Aromatic compounds resemble reactions of saturated rather than unsaturated hydrocarbons because the ring system is not destroyed and therefore resist addition of substituent groups within the pi bonds
• Ignition test results


  • Benzene - luminous flame, presence of soot
  • Cyclohexane - luminous flame, presence of soot
  • Gasoline - non-luminous flame, absence of soot
  • Kerosene - non-luminous flame, absence of soot
  • n-Hexane - luminous flame, presence of soot
• Luminous flame


  Burns brightly yellow flame, indicates incomplete combustion
• Non-luminous flame


  Burns almost invisible blue flame, indicates complete combustion
• Combustion reaction


  Hydrocarbon reacts with oxygen to produce carbon dioxide, water, and heat
• Incomplete combustion reaction produces carbon, carbon monoxide, and water as products instead of carbon dioxide
• When a fuel (e.g. gasoline, kerosene) burns in plenty of air, it receives enough oxygen for complete combustion, thereby producing non-luminous flame
• When a fuel burns in a limited space (e.g. car engine), there is no enough oxygen to completely oxidize the fuel, thereby producing black smoke/soot
• Baeyer's test for unsaturation results

  • Benzene - purple-colored solution
  • Cyclohexane - purple-colored solution
  • Gasoline - dark-brown precipitate
  • Kerosene - reddish-brown precipitate
  • n-Hexane - purple-colored solution
• Baeyer's test for unsaturation


  Used as a qualitative test for unsaturation, where reaction with double or triple bonds causes the color to fade from purple to brown precipitate
• Oxidation reaction in Baeyer's test

  1. Alkene is oxidized by KMnO4 producing products of a diol, manganese dioxide (MnO2) and permanganate ion (MnO4-)

  2. Alkyne is oxidized by KMnO4 producing products of a compound with four hydroxyl groups, manganese dioxide (MnO2) and permanganate ion (MnO4-)
• Bromine test for unsaturation results

  • Benzene - yellow-colored solution
  • Cyclohexane - yellow-colored solution
  • Gasoline - clear pinkish solution
  • Kerosene - clear colorless solution
  • n-Hexane - yellow-colored solution
• Bromine test for unsaturation

  Used as a qualitative test for unsaturation, where reaction with double or triple bonds causes the color to fade from brown to clear colorless solution
• Addition reaction in bromine test

  1. Alkene reacts with Br2 producing a dibromo product

  2. Alkyne reacts with Br2 producing a tetrabromo product
• Test for aromaticity (nitration) results

  • Benzene - pale yellow-colored layer in solution
  • Cyclohexane - clear colorless solution
  • Gasoline - deep yellow-colored layer in solution
  • Kerosene - yellow-colored layer in solution
  • n-Hexane - clear colorless solution
• Test for aromaticity (nitration)


  Benzene is nitrated using a nitrating acid (HNO3 + H2SO4) to produce nitrobenzene, which forms a yellow colored layer in solution after warming the test sample. This predicts the presence of aromatic ring through the formation of this yellow layer.
• Electrophilic aromatic substitution: Nitration of benzene


  Nitration of benzene firstly involves the formation of a very powerful electrophile, the nitronium ion, which is linear. This occurs following the interaction of sulfuric and nitric acid. Benzene then attacks the positively charged nitrogen atom of the electrophile, where one of the N=O bonds is broken at the same time. This is followed by rapid loss of a proton to regenerate the aromaticity.
• Alkanes are saturated hydrocarbons with single bonds between carbon atoms, while alkenes have double bonds.
• The functional group is the part of an organic molecule that determines its chemical properties.
• Aromatic compounds contain benzene rings and exhibit unique physical and chemical properties.
• Alcohols


  Organic compounds composed of an aliphatic carbon atom with a hydroxyl (-OH) functional group
• Hydroxyl group


  Functional group of all alcohols, hence the general formula of ROH, where R is the alkyl group
• Alcohols


  • Exhibit some unique set of physicochemical properties mainly due to the presence of the hydroxyl functional group
  • Some properties depend on the length of the alkyl chain attached to the hydroxyl group
• Ethanol (ethyl alcohol)


  The active component of alcoholic beverages, is just one and most common among the large family of alcohols