# What's the evidence that it is the nitronium cation (NO2+) acting as the attacking electrophile in mixed acid nitration of aromatic compounds (SeAr)

As per the title, I'm looking as to what is the evidence is that it is the $\ce{NO2+}$ cation acting as the attacking electrophile in an electrophillic aromatic substitution reaction involving the 'mixed acid' reagents of $\ce{H2SO4 + HNO3}$

I have considered the following although I feel as if other explanations exist and doesn't really specifically tackle the question:

The generation of the electrophile is as follows

$$\ce{2 H2SO4 + HNO3 -> H3O+ + NO2+ + 2 HSO4-}$$

Of which has been shown to be valid via spectroscopy methods & being consistent with the expected freezing-point depression. The $\ce{NO2+}$ cation can be trapped within unreactive anions (such as $\ce{BF4-},\ce{PF6-}$) to form salts which can then themselves act as nitrating agents to obtain the same nitration reaction product.

• Water will be protonated to $\ce{H3O+}$ in this medium. – Oscar Lanzi Nov 24 '17 at 14:24
• Can you be more specific? What are some alternatives that you have considered? – TAR86 Dec 10 '17 at 19:57