Which of the following minor products could NOT arise from the halogenation rxn below?
2-methylpropane + Br2 -> 1-bromo-2-methylpropane + HBr + minor products
a) 2,5-dimethyl hexane
b) 2-bromo-2-methylpropane
c) 1,3-dibromo-2-methylpropane
d) 2,4-dimethylhexane
e) 2,2,4 trimethylpentane
To determine which of the listed products could NOT arise from the given halogenation reaction, we need to analyze the reaction mechanism and the structure of each compound.
The halogenation reaction involves the substitution of a hydrogen atom in 2-methylpropane with a bromine atom. This reaction follows a free radical mechanism, where a chlorine atom is generated as a reactive intermediate. The bromine atom replaces a hydrogen atom in 2-methylpropane, resulting in 1-bromo-2-methylpropane. Additionally, hydrogen bromide (HBr) is produced as a byproduct.
Now let's analyze each of the listed compounds:
a) 2,5-dimethyl hexane: This compound has two methyl groups attached to a hexane chain. In the given halogenation reaction, there are no conditions for substituting hydrogens in distant positions or on different chains. Therefore, 2,5-dimethyl hexane cannot arise as a product of this reaction.
b) 2-bromo-2-methylpropane: This compound is one of the expected products of the reaction. It is formed by the substitution of a hydrogen atom in 2-methylpropane with a bromine atom.
c) 1,3-dibromo-2-methylpropane: This compound has two bromine atoms attached to different carbons in the 2-methylpropane structure. Although bromine substitution occurs in the reaction, it is not possible to have two bromine atoms substituted at different carbons through this reaction. Therefore, 1,3-dibromo-2-methylpropane cannot arise as a product.
d) 2,4-dimethylhexane: This compound is not directly related to the structure of the reactant 2-methylpropane. It has a different carbon chain without any substitution of hydrogen atoms. Therefore, 2,4-dimethylhexane cannot arise as a product.
e) 2,2,4-trimethylpentane: Similar to compound (d), this compound is not directly related to the structure of the reactant. It has a different carbon chain without any substitution of hydrogen atoms. Therefore, 2,2,4-trimethylpentane cannot arise as a product.
In conclusion, the minor product that could NOT arise from the halogenation reaction is c) 1,3-dibromo-2-methylpropane.