Isomers

• Compounds with the same molecular formula but different atomic arrangements.
• Constitutional isomers differ in the order in which atoms are connected.

Constitutional Isomers: Alkyl Substituents

Example: Constitutional Isomers of C₄H₁₀

• Butane: Continuous 4-carbon chain
• 2-Methylpropane: 3-carbon chain with 1 substituent

These structural differences define distinct compounds with different physical and chemical properties (e.g., boiling points differ by ~11°C).

The branched nature of 2-Methylpropane reduces potential contact between molecules causing reduced intermolecular dispersion forces

Constitutional Isomers: Non-Alkyl Substituents

• Substituting a heteroatom for a hydrogen atom in an alkane creates various constitutional isomers.
• Haloalkanes (Alkyl Halides): Replacing an alkane hydrogen with a halogen results in a class of compounds called haloalkanes or alkyl halides.

Example: Constitutional Isomers of C₃H₇Cl

• 1-Chloropropane
• 2-Chloropropane

Functional Groups

• The carbon-halogen bond in haloalkanes is considered a functional group.
• Functional groups exhibit predictable chemical behavior and are the reactive centers of parent carbon chains.

Table 7.4: Common Halogen Substituents

Drawing constitutional isomers

1. Determine all parent geometries
2. determine all hydrogen environments
3. determine all isomers