Which is not an electrophile?

• A. NO₂⁺
• B. CH₃ - CH₂⁺
• C. PCl₅
• D. CH₃⁺

To determine which option is not an electrophile, let's first understand what an electrophile is. Electrophiles are species that accept electrons during a chemical reaction, typically possessing a positive charge or a partial positive charge.

Analyzing the Options

• NO₂⁺: This is a nitronium ion, which is a strong electrophile due to its positive charge.
• CH₃ - CH₂⁺: This is a primary carbocation, also an electrophile because it can accept electrons.
• PCl₅: Phosphorus pentachloride can act as an electrophile in certain reactions, but it is more commonly known as a Lewis acid.
• CH₃⁺: This is a methyl cation, which is a well-known electrophile.

Identifying the Non-Electrophile

Among the options, PCl₅ is the least likely to be classified strictly as an electrophile in the same way the others are. While it can participate in reactions as a Lewis acid, it does not fit the typical definition of an electrophile that accepts electrons directly.

Therefore, the answer is PCl₅.