Among the following number of meta directing groups are: –CN, –NO₂, –COOH, –CH₃, –SO₃H, –NH₃ , –F

The correct answer is 5.

To determine the number of meta-directing groups among the given list, we need to analyze the electronic effects of each substituent on the benzene ring.

Substituents on a benzene ring are classified as ortho/para-directing or meta-directing based on their resonance and inductive effects:
1. Electron-withdrawing groups (EWGs): Groups that deactivate the benzene ring by withdrawing electron density via resonance (-M effect) or induction (-I effect) are generally meta-directing. These groups decrease electron density at all positions of the ring, but the deactivation is least severe at the meta position.
2. Electron-donating groups (EDGs): Groups that donate electron density to the ring via resonance (+M effect) or hyperconjugation/induction (+I effect) are ortho/para-directing. Halogens (like -F) are deactivating due to their strong -I effect, but they are ortho/para-directing due to their +M resonance effect.

Let's analyze each group given in the question:

1. -CN (Cyano group):
The nitrogen atom is highly electronegative and is connected to carbon by a triple bond. It strongly withdraws electron density from the ring via resonance (-M) and induction (-I). Thus, it is a meta-directing group.

2. -NO₂ (Nitro group):
The nitrogen atom carries a formal positive charge and is bonded to electronegative oxygen atoms. It is one of the strongest electron-withdrawing groups via both resonance (-M) and induction (-I). Thus, it is a meta-directing group.

3. -COOH (Carboxylic acid group):
The carbonyl carbon is electron-deficient due to the electronegative oxygen double bond, withdrawing electron density from the ring via resonance (-M) and induction (-I). Thus, it is a meta-directing group.

4. -CH₃ (Methyl group):
Alkyl groups donate electron density to the ring through hyperconjugation and inductive effect (+I). Thus, it is an activating, ortho/para-directing group.

5. -SO₃H (Sulfonic acid group):
The sulfur atom is bonded to three electronegative oxygen atoms, making it highly electron-deficient. It strongly withdraws electron density via resonance and induction. Thus, it is a meta-directing group.

6. -NH₃⁺ (Ammonium group):
The nitrogen atom carries a full positive charge and has no lone pair of electrons to donate. It strongly withdraws electron density through a powerful inductive effect (-I). Thus, it is a strongly deactivating, meta-directing group.

7. -F (Fluoro group):
Halogens have lone pairs on the key atom adjacent to the ring, allowing them to donate electron density through resonance (+M), which directs incoming electrophiles to the ortho and para positions, despite their overall deactivating nature due to their strong inductive effect (-I). Thus, it is an ortho/para-directing group.

Therefore, the meta-directing groups from the list are:
-CN, -NO₂, -COOH, -SO₃H, and -NH₃⁺.

Counting these groups: 1 (-CN) + 1 (-NO₂) + 1 (-COOH) + 1 (-SO₃H) + 1 (-NH₃⁺) = 5.