Question

Write a balanced chemical equation for the reaction that is described and then classify the reaction as a substitution, an elimination, an addition, or a rearrangement reaction. (a) 3,3 -dimethyl- 1 -butene reacts in acid solution to yield 2,3-dimethyl-2-butene. (b) 1 -iodo-2,2-dimethylpropane reacts with water, 2,2-dimethyl-1-propanol, and HI(aq). (c) 2-chloro-2-methylpropane reacts with NaOH(aq) to give 2 -methyl- 1 -propene, sodium chloride, and water.

Short answer

(a) is a rearrangement reaction given by the equation \( (CH_3)_3C-CH=CH_2 + H^{+} \rightarrow (CH_3)_3C-CH_2-CH_3 \). (b) is a substitution reaction: \( (CH_3)_3CI + H_2O \rightarrow (CH_3)_3COH + HI \). (c) This is an elimination reaction: \( (CH_3)_3CCl + NaOH \rightarrow (CH_3)_2C=CH_2 + NaCl + H_2O \).

Step-by-step solution

- Reaction (a)

Observing 3,3-dimethyl-1-butene reacts in an acid solution to yield 2,3-dimethyl-2-butene, the process implies a rearrangement occurs. Thus, the reaction can be written as \( (CH_3)_3C-CH=CH_2 + H^{+} \rightarrow (CH_3)_3C-CH_2-CH_3 \). This is considered a rearrangement reaction.

- Reaction (b)

1-iodo-2,2-dimethylpropane reacting with water gives 2,2-dimethyl-1-propanol and HI(aq). This can be represented as \( (CH_3)_3CI + H_2O \rightarrow (CH_3)_3COH + HI \). This is a substitution reaction, where iodine has been replaced by hydroxyl group owing to its reaction with water.

- Reaction (c)

2-chloro-2-methylpropane reacting with NaOH(aq) gives 2-methyl-1-propene, sodium chloride, and water. The equation for the reaction is \( (CH_3)_3CCl + NaOH \rightarrow (CH_3)_2C=CH_2 + NaCl + H_2O \). This reaction is an elimination reaction, where chlorine on the 2-chloro-2-methylpropane is replaced with a hydrogen, effectively eliminating a molecule of water and forming the double bond in the product.

Key concepts

Rearrangement Reaction

Rearrangement reactions involve the structural reorganization of atoms within a molecule. When 3,3-dimethyl-1-butene reacts in an acid solution to form 2,3-dimethyl-2-butene, it undergoes a rearrangement. This means the connectivity of atoms changes, but the molecular formula remains the same.

• The main factor driving rearrangement is often the stability gained by the new structure.
• Such reactions are common in organic compounds where the product is more stable than the reactant.

Imagine rearranging building blocks into a different shape without adding or removing any pieces. This is similar to what happens during a rearrangement reaction.

Substitution Reaction

Substitution reactions occur when an atom or group within a molecule is replaced by another atom or group. In our example, 1-iodo-2,2-dimethylpropane reacts with water to form 2,2-dimethyl-1-propanol and HI, illustrating a substitution reaction. Here, the iodine is replaced by a hydroxyl group.

• Substitution reactions are prevalent in organic chemistry, especially in halogenated compounds.
• This type can further be classified into nucleophilic and electrophilic substitution based on the nature of the substituting species.

Think of substitution reactions like swapping pieces in a puzzle—one piece is taken out and another is put in its place.

Elimination Reaction

Elimination reactions involve the removal of elements from a molecule resulting in the formation of a double bond. When 2-chloro-2-methylpropane reacts with NaOH, producing 2-methyl-1-propene, sodium chloride, and water, an elimination reaction occurs. This process eliminates hydrogen and chlorine to form a double bond.

• These reactions often compete with substitution reactions.
• They can result in the formation of alkenes, which have carbon-carbon double bonds.

Think of this as removing pieces from a structure, resulting in a leaner, tighter design, akin to tightening a belt to form new connections.