Question

Which of the following will be most stable diazonium salt $(R\, N^{+}_{2}\,X^{-})$ ?

• A. $CH_3 N_2^+X^-$
• B. $C_6H_5 N_2^+X^-$
• C. $CH_3 CH_2 N_2^+X^-$
• D. $C_6H_5 CH_2 N_2^+X^-$

Answer 1

The Correct Option is B

The stability of diazonium salts R\, N_2^+X^-\ largely depends on the ability of the substituent R to stabilize the positive charge on the nitrogen atom. Typically, aromatic or conjugated systems provide stabilization through resonance, which increases the overall stability of the diazonium ion.

1. Stability of Aliphatic Diazonium Salts:
   • Aliphatic diazonium ions such as CH_3N_2^+X^-\ and CH_3CH_2N_2^+X^-\ are generally unstable because they lack the ability to delocalize the positive charge effectively. Without resonance stabilization, these ions rapidly decompose to form nitrogen gas and other byproducts.
2. Stability in Benzilic Systems:
   • The compound C_6H_5N_2^+X^-\ (benzenediazonium ion) is much more stable due to resonance stabilization. The aromatic ring can delocalize the positive charge over the entire ring structure, leading to enhanced stability.
   • This resonance stabilization is key to the stability of aryl diazonium salts and is not present in aliphatic counterparts.
3. Role of Benzyl Group:
   • A diazonium ion formed on a benzyl group such as C_6H_5CH_2N_2^+X^-\ is also not as stable as the benzenediazonium ion because the resonance structure does not effectively extend into the aromatic ring capably as compared to the benzene directly attached to the diazo group.

In conclusion, based on resonance stabilization, the most stable diazonium salt is C_6H_5N_2^+X^- due to the effective delocalization of the charge across the aromatic ring.