HYDROCARBONS CHEMISTRY, Lecture notes of Chemistry

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The

Hydrocarbons

Antonio G. Celajes Jr., RCh

WCC Prayer

Today’s Learning Objectives

At the end of the lesson, the students will be able to propose correct names of hydrocarbons as well

as their importance.

The Hydrocarbons

a. Aliphatic and Alicyclic Hydrocarbons

b. Aromatic Hydrocarbons

c. Nomenclature of Hydrocarbons

d. Properties, Usage and Applications of Hydrocarbons

The Hydrocarbons

Hydrocarbon Aliphatic Alkanes (Saturated) Alkenes (Unsaturated) Alkynes (Unsaturated) Alicyclic Cycloalkane Cycloalkene Cycloalkyne Aromatic Benzene Benzene Derivatives Other Aromatic Compounds

Nomenclature of Hydrocarbon

• Use prefix from the Homologous Series to indicate number of carbons
• For aliphatic HC, add
  • • ane for alkane
  • • ene for alkene
  • • yne for alkyne
• For alicyclic HC,
  • Preceded by cyclo- then add - ane for cycloalkane
  • Preceded by cyclo- then add - ene for cycloalkane
  • Preceded by cyclo- then add - ene for cycloalkane

The Alkanes (Paraffins): IUPAC Nomenclature of Alkanes

• Find and name the longest continuous carbon chain
• Identify and name groups attached to this chain and name them by using suffix - yl
• Number the chain consecutively, starting at the end nearest a substituent group
• Designate the location of each substituent group by an appropriate number and name
• Assemble the name, listing groups in alphabetical order using the full name (e.g. cyclopropyl before isobutyl)
• The prefixes di, tri, tetra etc., used to designate several groups of the same kind, are not considered when alphabetizing.

The Alkanes: Isomerism in Alkanes

• Structural / Constitutional Isomerism
  • a form of isomerism in which molecules with the same molecular formula have different bonding patterns and atomic organization
    • Skeletal / Chain Isomerism – same molecular formula but different arrangement of carbon skeleton, found in alkanes
    • Positional Isomerism – same molecular formula but different position of multiple bond or functional group, found alkenes, alkynes, alcohols, etc.
    • Functional Isomerism – same molecular formula but different functional group present i.e ketone is the functional isomer of aldehydes, cycloalkane is the functional isomer of alkene
  • Alkanes exhibit Skeletal / Chain isomerism
    • components of the (usually carbon) skeleton are distinctly re-ordered to create different structures
    • Example: n-pentane is the skeletal isomer of isopentane and neopentane

The Alkanes: Isomerism in Alkanes

• Stereoisomerism
  • a form of isomerism in which molecules with the same molecular formula have different spatial arrangement of carbon atoms
    • Conformational isomerism – same molecular formula but different spatial arrangement of groups attached to carbons due to rotation, applicable to alkanes
    • Cis and trans (E-Z) isomerism – same molecular formula but different spatial arrangement of groups attached to doubly bonded carbon, applicable to alkenes
    • Optical Isomerism – same molecular formula but different spatial arrangement of groups attached to chiral carbon (carbon with four different groups attached), could be enantiomers or diastereomers
  • Alkanes exhibit conformational isomerism
    • Conformation – can be eclipsed (least stable), gauched and staggered (most stable) conformation and may be written as:
      • Newman projection
      • Sawhorse projection

The Alkanes: General Properties

• Chemical Properties
  • Reaction with Oxygen
    • Alkanes react with oxygen through combustion to produce CO 2 and H 2 O under excess oxygen
    • Produce CO, H 2 O and Free Carbon under insufficient oxygen
  • Reaction with Halogens
    • Follows substitution reaction when reacting with a halogen through free radical formation
    • Free radical – group of element with unpaired electron, highly reactive and unstable

The Alkanes: Occurrence and Applications

Occurrence

• Found in the atmosphere of giant gas planets such as Jupiter, Saturn and Uranus
• Found in Oil and gas fields as by products of anaerobic decomposition of organic matter i.e

dinosaur

• Respiration product of bacteria and archaea (methanogens)

Applications

• Fuels and lubricants
• Candles

Cycloalkanes: Isomerism in Cycloalkanes

• Some cycloalkanes exhibit conformational isomerism
  • Cyclohexane – has boat and chair conformational isomers
  • Cyclopentane – has envelop conformational isomers

Cycloalkanes: General Properties of Cycloalkanes

• Cycloalkane has similar trending as alkanes when it comes to density, boiling

and melting points;

• Cycloalkanes exhibit similar reactions as alkanes

The Alkenes (Olefins) and Alkynes (Acetylenes): Common Nomenclature of Alkenes and Alkynes

• Alkenes
  • Common / trivial names are for straight, unsubstituted alkene only
  • Name the groups attached to doubly bonded carbon then name them with – yl ending
  • Arrange them alphabetically then add - ethylene
• Alkynes
  • Common / trivial names are for straight, unsubstituted alkyne only
  • Name the groups attached to triply bonded carbon then name them with – yl ending
  • Arrange them alphabetically then add - acetylene

The Alkenes and Alkynes: General Properties of Alkenes and Alkynes

• Physical Properties
  • Usually similar with alkanes but alkenes and alkynes have stronger odor than alkanes
• Chemical Properties
  • Alkenes and alkynes are more reactive than alkanes and generally follows addition reaction;
  • The pi bonds are usually the site of reactions among alkenes and alkynes