Question

The set of meta directing functional groups from the following sets is:

• A. –CN, –NH\(_2\), –NHR, –OCH\(_3\)
• B. –NO\(_2\), –NH\(_2\), –COOH, –COOR
• C. –NO\(_2\), –CHO, –SO\(_3\)H, –COR
• D. –CN, –CHO, –NHCOCH\(_3\), –COOR

Answer 1

The Correct Option is C

To determine which set of functional groups are meta directing, we need to know about the electronic effects these groups have when attached to an aromatic ring. Meta directing groups withdraw electron density from the benzene ring through resonance or inductive effects, making the meta position relatively electron-rich compared to ortho and para positions. Here, we'll analyze the given options: 

1. Option 1: –CN, –NH₂, –NHR, –OCH₃
   • –CN is a meta director because it is an electron-withdrawing group.
   • –NH₂ and –NHR are electron-donating groups, typically ortho/para directing.
   • –OCH₃ is also an electron-donating group, which directs to ortho/para positions.
   • Thus, this set contains both meta and ortho/para directors.
2. Option 2: –NO₂, –NH₂, –COOH, –COOR
   • –NO₂, –COOH, and –COOR are electron-withdrawing groups and hence are meta directors.
   • –NH₂ is an electron-donating group and is ortho/para directing.
   • This set also contains both types of directors.
3. Option 3: –NO₂, –CHO, –SO₃H, –COR
   • All these groups (–NO₂, –CHO, –SO₃H, and –COR) are electron-withdrawing by both resonance and inductive effects.
   • Meta Directors: These groups withdraw electron density and stabilize the meta position during electrophilic substitution.
   • Therefore, this entire set is comprised of meta directors.
4. Option 4: –CN, –CHO, –NHCOCH₃, –COOR
   • –CN, –CHO, and –COOR are electron-withdrawing and meta directing.
   • However, –NHCOCH₃ can have a different effect due to its resonance donation capabilities under certain conditions, primarily neither strongly directing to meta or ortho/para.
   • This set has a majority of meta directors but isn't entirely consistent.

Based on the above analysis, the correct set which completely consists of meta directing groups is Option 3: –NO₂, –CHO, –SO₃H, –COR. These groups withdraw electrons from the aromatic ring and direct further substitution to the meta position.

Answer 2

Meta directing groups are typically electron-withdrawing groups (EWGs) that deactivate the benzene ring and direct incoming electrophiles to the meta position relative to themselves. This is due to their ability to withdraw electron density from the ortho and para positions, making these positions less reactive to electrophilic substitution reactions.
Explanation of Each Functional Group Set
Option (1): Groups like --NH$_2$, --NHR, and --OCH$_3$ are electron-donating and act as ortho/para directors, not meta directors.
Option (2): While --NO$_2$ and --COOH are meta directing, --NH$_2$ is an electron-donating group and acts as an ortho/para director.
Option (3): Groups --NO$_2$, --CHO, --SO$_3$H, and --COR are strong electron-withdrawing groups and are known meta directors.
Option (4): --NHCOCH$_3$ and --COOR are electron-withdrawing groups but are less effective meta directors compared to the strong meta directing groups in Option (3).
Conclusion: The correct set of meta directing functional groups is --NO$_2$, --CHO, --SO$_3$H, --COR.