What is the Difference Between 1 2 Addition and 1 4 Addition?

The main difference between 1,2-addition and 1,4-addition lies in the position of the carbon atoms in the conjugated diene that are involved in the addition reaction. In a 1,2-addition, the reactant adds to the first and second carbon atoms of the diene, resulting in a product where the added atoms or groups are adjacent to each other. In a 1,4-addition, the reactant adds to the first and fourth carbon atoms of the diene, resulting in a product where the added atoms or groups are separated by two carbon atoms.

Here are some key points about 1,2- and 1,4-additions:

• The 1,2-addition has a smaller activation energy than the 1,4-addition, making it occur faster.
• At low temperatures, the 1,2-addition product is favored, while at higher temperatures, the 1,4-addition product becomes more dominant.
• The 1,4-addition product is more thermodynamically stable than the 1,2-addition product due to its more substituted double bond.

For example, when HBr is added to butadiene, the 1,2-addition product is formed when HBr bonds to the first carbon atom and the Br bonds to the second carbon atom, resulting in 1-bromo-2-butene. The 1,4-addition product is formed when HBr bonds to the first carbon atom and the Br bonds to the fourth carbon atom, resulting in 2-bromo-1-butene.

Comparative Table: 1 2 Addition vs 1 4 Addition

The difference between 1,2-addition and 1,4-addition lies in the position at which the new attacking molecule bonds to the double bond of a conjugated diene. Here is a summary of the two types of addition:

At low temperatures, the products are formed irreversibly and reflect the relative rates of the two competing reactions. As the temperature increases, the amount of 1,4 product increases.