Elimination Reactions
In elimination reactions, single bond molecules (alkanes), becomes double bond molecules (alkenes), giving off a smaller molecule.
So this the removal of a molecule from a larger one.
"alkane → alkene + something"
DEHYDROHALOGENATION
de-hydro-halogenation
removal of a halogen
HCl is removed form the organic molecule
Reaction Condition
• conc NaOH / KOH or
• NaOH / KOH dissolved in ethanol

Diagram 1
- Chloroethane is on the left, and becomes ethene.
- The H and Cl from separate carbons are removed.
- These leftover bonds join up to become a double bond
- The H and Cl becomes HCl
- The organic molecule is that much smaller.
DEHYDRATION
de-hydration
removal of water H2O from the alcohol organic compound
Reaction Condition
• H2SO4
• hot catalyst

Diagram 2
- The left is an alcohol, ethanol
- The H and OH are eliminated.
- The leftover bonds join to become a double bond molecule, ethene.
- Water H2O is eliminated from the ethanol and is produced.
CRACKING
breaking large alkanes into smaller alkenes and alkanes.
typically in the fuel industry
Reaction Condition
• Pt catalyst (platinum)
• 8000C
Diagram 3
- Left Hand Side:
Number of C = 7
Number of H = 16
- Right Hand Side:
Number of C = 2 + 5 = 7
Number of H = 4 + 12 = 16
- Notice that both sides have the same number of individual atoms