Notes on Nonpolar Molecules

Nonpolar Molecules

Properties

• Melting and boiling points increase with the number of carbons in the parent chain.
• Highly flammable.
• Unsaturated hydrocarbons (containing double or triple bonds) are more reactive than saturated hydrocarbons (containing only single bonds).
• Alkenes and alkynes can form polymers (large molecules).
• Generally colorless and odorless.

Cyclic (Ring Structures)

• Cyclic hydrocarbons connect to form a ring.
• To name them:
  • Identify the parent ring and name it.
  • The name begins with "cyclo-", followed by a prefix for the number of carbons, and ends with "-ane" (single bonds), "-ene" (one double bond), or "-yne" (one triple bond).
  • Examples: cyclobutane, cyclopentene, cyclooctyne.
  • Number the carbons in the ring, with a multiple bond (if present) always labeled as carbon 1.
  • Name the alkyl groups attached to the ring. Use prefixes (di-, tri-, etc.) if there are multiple identical alkyl groups.
  • Show the positions of the alkyl groups with numbers.
• Examples:
  • 1,3-dimethylcyclopentane
  • 3-ethyl-1-cyclohexene
  • 1,4-cyclohexadiene
  • 2,3-dimethylhexane (This example is not a cyclic structure, but is listed among the examples in the source material)

Aromatics

• Contain benzene, which is a cyclohexene with alternating double bonds.
• Formula for benzene: $C<em>6H</em>6$
• Generally have a strong pleasant odor.

Structural Isomers

• Structural isomers are isomers with the same number of carbons but different arrangements/structures.
• Example: Pentane ($C<em>5H</em>{12}$) has 3 isomers: pentane, 2-methylbutane, and 2,2-dimethylpropane.

Geometric Isomers

• Geometric isomers result from different arrangements across a double bond.
• cis- isomers: substituents are on the same side of the double bond.
• trans- isomers: substituents are on opposite sides of the double bond.