Definitions [3]
Definition: Alkanes
Alkanes are hydrocarbons in which all the linkages between the carbon atoms are single covalent bonds.
Definition: Alkenes
Alkenes are compounds with at least one carbon-carbon double bond. Alkenes form a homologous series having the general formula Cn H2n
Definition: Alkynes
The aliphatic hydrocarbons that contain a triple bond (-C = C-), i.e., acetylenic bond, between two carbon atoms are known as alkynes. The general formula CnH2n-2.
Key Points
Key Points: Alkanes
- General formula: CₙH₂ₙ₊₂ (where n = number of carbon atoms)
- Suffix used for IUPAC naming: –ane
- e.g., Methane (CH₄), Ethane (C₂H₆), Propane (C₃H₈)
- Alkanes exhibit chain isomerism due to absence of any functional group and the possibility of more than one chain type for the same molecular formula
- e.g., C₅H₁₂ forms n-pentane, neo-pentane, and iso-pentane
Conformations in Alkanes:
Conformation = spatial arrangement of atoms that can be interconverted by rotation about a C–C single bond. Also called conformers or rotamers.
For ethane, two extreme conformations exist:
| Conformation | Description | Energy | Stability |
|---|---|---|---|
| Eclipsed | Hydrogen atoms on adjacent carbons are as close as possible | Maximum energy | Highly unstable |
| Staggered | Hydrogen atoms are as far apart as possible | Minimum energy | Highly stable |
Skew conformation is an intermediate between eclipsed and staggered conformations. Both are represented by Sawhorse and Newman projections.
Sawhorse formula of ethane
Newmann projection formula ethane
