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Which of the following species is not electrophilic in nature?
A
$Cl^+$
B
$BH_3$
C
$H_3O^+$
D
$NO_2^+$
Detailed Solution
An electrophile is an electron-deficient species that can accept a pair of electrons; it needs a vacant orbital (or an atom able to take up a pair).
$Cl^+$ has only six valence electrons, so it is electron deficient and electrophilic.
$BH_3$ has only six electrons around boron and an empty p orbital; it is electrophilic.
$NO_2^+$ (nitronium ion) has an electron-deficient nitrogen that accepts an electron pair in nitration; it is electrophilic.
$H_3O^+$: although it carries a positive charge, oxygen already has a complete octet (three bond pairs and one lone pair) and has no vacant orbital, so it cannot accept an electron pair.
Hence $H_3O^+$ is not electrophilic.
$Cl^+$ has only six valence electrons, so it is electron deficient and electrophilic.
$BH_3$ has only six electrons around boron and an empty p orbital; it is electrophilic.
$NO_2^+$ (nitronium ion) has an electron-deficient nitrogen that accepts an electron pair in nitration; it is electrophilic.
$H_3O^+$: although it carries a positive charge, oxygen already has a complete octet (three bond pairs and one lone pair) and has no vacant orbital, so it cannot accept an electron pair.
Hence $H_3O^+$ is not electrophilic.