What is the substitution reaction?

What is the substitution reaction?

• A. Reactants put under a bright light with bromine water.
• B. Reactants are heated with oxygen.
• C. Reactants are dissolved in acid.
• D. Reactants are treated with base to form salts.

Answer: (A)

Substitution reactions involve replacing one atom or group in a molecule with another. In organic chemistry, a common substitution is halogenation of alkanes, where a hydrogen atom in an alkane is replaced by a halogen atom. When reactants are exposed to bright light in the presence of bromine water, bromine molecules absorb energy and form bromine radicals. These radicals initiate a chain reaction that replaces a hydrogen on the alkane with bromine, producing a bromoalkane and hydrogen bromide. The bromine water decolorizes as bromine is consumed, which is a visual sign that substitution is occurring. Other scenarios don’t involve replacing a hydrogen with a halogen on the carbon skeleton. Heating with oxygen leads to combustion, not substitution. Dissolving in acid or reacting with base to form salts typically results in other types of reactions, not hydrogen being swapped for a halogen.

Substitution reactions involve replacing one atom or group in a molecule with another. In organic chemistry, a common substitution is halogenation of alkanes, where a hydrogen atom in an alkane is replaced by a halogen atom.

When reactants are exposed to bright light in the presence of bromine water, bromine molecules absorb energy and form bromine radicals. These radicals initiate a chain reaction that replaces a hydrogen on the alkane with bromine, producing a bromoalkane and hydrogen bromide. The bromine water decolorizes as bromine is consumed, which is a visual sign that substitution is occurring.

Other scenarios don’t involve replacing a hydrogen with a halogen on the carbon skeleton. Heating with oxygen leads to combustion, not substitution. Dissolving in acid or reacting with base to form salts typically results in other types of reactions, not hydrogen being swapped for a halogen.