Steric factors refer to the effect of the size and shape of molecules on the rate of a chemical reaction. They are important because molecules must collide in the correct orientation for a reaction to occur.
Significance in Reaction Rates (Simple Explanation):
- Molecular crowding:
- Large or bulky groups in a molecule can block access to the reactive site.
- This makes it harder for reactants to collide properly, slowing the reaction.
- Orientation of collision:
- For a reaction, molecules must collide in a specific way (correct angle or orientation).
- Steric hindrance can prevent proper alignment, reducing the reaction rate.
- Selective reactions:
- Steric factors can influence which reactions happen when multiple possibilities exist.
- This is important in organic synthesis to produce the desired product.
Example:
- Tertiary alkyl halides react more slowly in SN2 reactions than primary ones because the bulky groups around the carbon block the nucleophile from attacking.
Simple idea:
- Steric factors = “molecular crowding or blocking” that can slow down or control how fast a reaction happens.