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
Condensed Structure | Name |
---|---|
−F | fluoro |
−Cl | chloro |
−Br | bromo |
−I | iodo |
Drawing constitutional isomers
- Determine all parent geometries
- determine all hydrogen environments
- determine all isomers