When an alkane is heated with bromine, it undergoes halogenation, which is a type of substitution reaction. In this reaction, one or more hydrogen atoms in the alkane are replaced by a halogen atom such as bromine. The reaction is typically carried out in the presence of a catalyst such as iron or aluminum.
What is Monobromination?
Monobromination is a type of halogenation in which only one hydrogen atom in the alkane is replaced by a bromine atom. The resulting product is called a monobrominated alkane. The major product formed during monobromination depends on the structure of the alkane.
Example of Monobromination of Alkanes
Let's take an example of monobromination of an alkane. Consider the reaction between methane (CH4) and bromine (Br2) in the presence of iron catalyst. The reaction can be represented as:
CH4 + Br2 ??? CH3Br + HBr
In this reaction, one hydrogen atom in methane is replaced by a bromine atom to form methyl bromide (CH3Br) and hydrogen bromide (HBr) is produced as a byproduct.
Monobromination of Propane
Now, let's consider the monobromination of propane (C3H8). Propane has three hydrogen atoms, any of which can be substituted by a bromine atom. However, the major product formed during monobromination of propane depends on the location of the hydrogen atom that is substituted.
Location of Hydrogen Atom Substitution
The three hydrogen atoms in propane are labeled as alpha, beta, and gamma. The alpha hydrogen atoms are those that are directly attached to the carbon atom that is bonded to two other carbon atoms. The beta hydrogen atoms are those that are attached to the carbon atom that is bonded to only one other carbon atom. The gamma hydrogen atom is the one that is attached to the carbon atom that is bonded to three other carbon atoms.
In the monobromination of propane, the major product formed depends on which hydrogen atom is substituted. If the alpha hydrogen atom is substituted, the product formed is 1-bromopropane. If the beta hydrogen atom is substituted, the product formed is 2-bromopropane. If the gamma hydrogen atom is substituted, the product formed is 2-bromo-2-methylpropane (also known as tert-butyl bromide).
Draw the Major Monobromination Product
Now, let's draw the major monobromination product formed by heating propane with bromine. Since the location of substitution determines the product formed, we need to consider each possibility.
1-Bromopropane
If the alpha hydrogen atom is substituted, the major product formed is 1-bromopropane. The reaction can be represented as:
2-Bromopropane
If the beta hydrogen atom is substituted, the major product formed is 2-bromopropane. The reaction can be represented as:
2-Bromo-2-Methylpropane
If the gamma hydrogen atom is substituted, the major product formed is 2-bromo-2-methylpropane. The reaction can be represented as:
Conclusion
In conclusion, monobromination is a type of halogenation in which one hydrogen atom in an alkane is replaced by a bromine atom. The major product formed during monobromination depends on the location of the hydrogen atom that is substituted. In the case of propane, three products can be formed depending on which hydrogen atom is substituted: 1-bromopropane, 2-bromopropane, and 2-bromo-2-methylpropane.
