Substitution and addition reactions are two important types of reactions that happen in organic chemistry. They have different styles, products, and uses. Let’s break them down in a simpler way.

Substitution Reactions

What Are They? In a substitution reaction, one atom or group of atoms in a molecule gets swapped out for another.

How Do They Work? There are two main ways this happens:

1. Nucleophilic Substitution (SN reactions): Here, a nucleophile, which is something that wants to give away an electron pair, makes a new bond while a different group leaves.
2. Electrophilic Substitution (SE reactions): In this case, an electrophile, which wants to grab electrons, attacks a spot in the molecule and replaces a certain atom or group.

Examples: A typical example would be changing haloalkanes to alcohols through nucleophilic substitution. Another example is the Friedel-Crafts reaction, which involves aromatic substitutions.

Key Points: These reactions usually keep the carbon structure of the original molecule. This means the new product looks quite a bit like the original reactant. The outcome depends on what groups are involved and the conditions when the reaction happens.

Addition Reactions

What Are They? Addition reactions happen when atoms or groups are added to a molecule that has multiple bonds, like in alkenes or alkynes.

How Do They Work? These reactions mainly occur in two ways:

1. Electrophilic Addition: An electrophile reacts with a nucleophile, often breaking a double bond in an alkene.
2. Nucleophilic Addition: This occurs with carbonyl compounds where the nucleophile goes after the carbon in a double bond to create a new bond.

Examples: One simple example is the hydrogenation of alkenes, where hydrogen (H₂) is added across a double bond, turning it into a fully saturated alkane.

Key Points: Addition reactions usually add more atoms to the product, making the molecule more complex. They can change the structure of molecules a lot, leading to various new functional groups and properties.

Key Differences

1. Type of Bonds:

   • Substitution reactions replace atoms or groups, keeping the main structure intact.
   • Addition reactions break double bonds and create new bonds, changing the structure.

2. Carbon Skeleton:

   • In substitution, the overall carbon skeleton stays the same.
   • In addition, new atoms are added to the carbon skeleton.

3. Product Variety:

   • Substitution reactions usually produce something that looks quite similar to the original.
   • Addition reactions can create a wide range of different products from simple starting materials.

Understanding these differences is really important for chemists. It helps them design better ways to build and change molecules for different purposes.