Draw the structure of the activated benzene ring and the diazonium ion used in the synthesis of each of the following compounds, whose structures can be found on page 607.
b. methyl orange

Verified step by step guidance

1. Identify the structure of methyl orange, which is an azo dye. It contains an azo group (-N=N-) linking two aromatic rings, one of which is substituted with a sulfonic acid group (-SO3H) and the other with a methyl group (-CH3).
2. Understand that the synthesis of methyl orange involves a diazonium coupling reaction. This reaction requires a diazonium ion and an activated benzene ring. The diazonium ion is typically derived from an aromatic amine through diazotization.
3. Determine the structure of the diazonium ion. In this case, the diazonium ion is derived from sulfanilic acid (an aromatic amine with a -SO3H group). The diazonium ion is formed by treating sulfanilic acid with sodium nitrite (NaNO2) and hydrochloric acid (HCl) under cold conditions, resulting in the structure: \( \text{C}_6\text{H}_4\text{SO}_3^-\text{N}_2^+ \).
4. Identify the activated benzene ring. The coupling partner in this reaction is N,N-dimethylaniline, which has a benzene ring activated by the electron-donating dimethylamino group (-N(CH3)2). This group increases the electron density on the benzene ring, making it more reactive toward electrophilic attack by the diazonium ion.
5. Combine the diazonium ion and the activated benzene ring. The diazonium ion acts as an electrophile and reacts with the activated benzene ring of N,N-dimethylaniline at the para position relative to the -N(CH3)2 group. This forms the azo bond (-N=N-) and results in the structure of methyl orange.

Key Concepts

Activated Benzene Ring

An activated benzene ring is a benzene derivative that has substituents that increase its reactivity towards electrophilic aromatic substitution. These substituents, such as -OH or -NH2, donate electron density to the ring, making it more nucleophilic. Understanding the structure and reactivity of activated benzene is crucial for predicting the outcomes of reactions involving electrophiles.

Diazonium Ion

A diazonium ion is a positively charged species with the general formula R-N2^+, where R is an aryl group. It is formed by the reaction of an aromatic amine with nitrous acid and is a key intermediate in various organic reactions, particularly in the synthesis of azo compounds. The diazonium ion can undergo substitution reactions to introduce new functional groups onto the aromatic ring.

Methyl Orange Structure

Methyl orange is a pH indicator that changes color based on the acidity of the solution. Its structure includes a diazo compound linked to a sulfonic acid group, which contributes to its solubility and color change properties. Understanding the molecular structure of methyl orange is essential for recognizing how it interacts with acids and bases, as well as its synthesis from diazonium ions.