Question

How many compounds among the following compounds show inductive, mesomeric as well as hyperconjugation effects?

• A. Methoxybenzene (Anisole)
• B. 3-Methylpent-3-en-2-one
• C. Benzene
• D. Chlorocyclohexane
• E. 2-Isopropyl-1-nitrobenzene
• F. 2-Allyl-1-nitrobenzene
• G. 3-Methylanisole (m-Methylanisole)
• H. 1-Acetyl-2,6-dimethylcyclohex-1-ene

Answer 1

6

Answer 2

Here's an analysis of each compound to determine if it exhibits inductive, mesomeric, and hyperconjugation effects:

1. Methoxybenzene (Anisole)

• Inductive Effect (I): Present due to the electronegativity difference between C and O in the C-O bond, and C-H bonds. Oxygen is electronegative (-I effect from O, +I effect from CH₃).
• Mesomeric Effect (M): Present. The lone pairs on the oxygen atom of the -OCH₃ group can be delocalized into the benzene ring, exhibiting a +M effect.
• Hyperconjugation (H): Present. The C-H bonds of the methyl group are adjacent to the oxygen atom, which is attached to the aromatic ring. These C-H sigma bonds can overlap with the adjacent C-O sigma bond or the pi system of the benzene ring, contributing to hyperconjugation.
  • Exhibits all three effects.

2. 3-Methylpent-3-en-2-one $\text{CH}_3-\text{CH}=\text{C}(\text{CH}_3)-\text{C}(=\text{O})-\text{CH}_3$

• Inductive Effect (I): Present due to C-C, C-H, C=C, and C=O bonds. Methyl groups are +I, carbonyl carbon is -I.
• Mesomeric Effect (M): Present. The C=C double bond is conjugated with the C=O double bond, allowing for resonance (electron delocalization). The C=O group exhibits a -M effect.
• Hyperconjugation (H): Present. There are alpha-hydrogens on the methyl group attached to the double bond (CH₃-CH=) and on the methyl group of the acetyl moiety (-C(=O)-CH₃). These hydrogens are adjacent to sp² hybridized carbons (double bond and carbonyl carbon attached to the double bond), allowing for hyperconjugation.
  • Exhibits all three effects.

3. Benzene

• Inductive Effect (I): Present due to C-C and C-H sigma bonds.
• Mesomeric Effect (M): Present. The delocalization of pi electrons in the aromatic ring is a mesomeric effect.
• Hyperconjugation (H): Not present. Benzene itself does not have alkyl substituents with alpha-hydrogens adjacent to a pi system or charged center.
  • Does not exhibit all three effects.

4. Chlorocyclohexane

• Inductive Effect (I): Present due to the electronegativity difference between C and Cl in the C-Cl bond (-I effect of Cl).
• Mesomeric Effect (M): Not present. There is no pi system or lone pair conjugation.
• Hyperconjugation (H): Not present. There are no double bonds, aromatic rings, carbocations, or radicals.
  • Does not exhibit all three effects.

5. 2-Isopropyl-1-nitrobenzene

• Inductive Effect (I): Present due to C-C, C-H bonds in the ring and isopropyl group. The nitro group (-NO₂) exhibits a strong -I effect. The isopropyl group exhibits a +I effect.
• Mesomeric Effect (M): Present. The nitro group (-NO₂) is directly attached to the benzene ring and exerts a strong -M effect.
• Hyperconjugation (H): Present. The isopropyl group [-CH(CH₃)₂] has methyl groups whose C-H bonds are alpha to the carbon attached to the benzene ring. These alpha-hydrogens can participate in hyperconjugation with the pi system of the benzene ring.
  • Exhibits all three effects.

6. 2-Allyl-1-nitrobenzene $\text{o-NO}_2\text{-C}_6\text{H}_4\text{-CH}_2\text{-CH}=\text{CH}_2$

• Inductive Effect (I): Present due to C-C, C-H bonds in the ring and allyl group. The nitro group (-NO₂) is -I. The allyl group has C=C, which influences electron distribution.
• Mesomeric Effect (M): Present. The nitro group (-NO₂) is directly attached to the benzene ring and exerts a strong -M effect.
• Hyperconjugation (H): Present. The allyl group (-CH₂-CH=CH₂) has alpha-hydrogens on the methylene group (-CH₂-) directly attached to the ring, and also alpha-hydrogens on the vinylic methylene group (-CH=CH₂). These contribute to hyperconjugation.
  • Exhibits all three effects.

7. 3-Methylanisole (m-Methylanisole)

• Inductive Effect (I): Present due to C-C, C-H bonds, and the C-O bond. -OCH₃ group is -I (due to O) and +I (due to CH₃). CH₃ group is +I.
• Mesomeric Effect (M): Present. The lone pairs on the oxygen atom of the -OCH₃ group can be delocalized into the benzene ring, exhibiting a +M effect.
• Hyperconjugation (H): Present. The C-H bonds of the methyl group (-CH₃) attached to the benzene ring can participate in hyperconjugation with the pi system of the ring.
  • Exhibits all three effects.

8. 1-Acetyl-2,6-dimethylcyclohex-1-ene (Assuming the structure is as depicted: a cyclohexene ring with a double bond, one carbon of the double bond has -COCH₃, the other has -CH₃, and a third -CH₃ is on a saturated carbon of the ring, likely at position 6 relative to the double bond).

• Inductive Effect (I): Present due to C-C, C-H, C=C, and C=O bonds. Methyl groups are +I, carbonyl carbon is -I.
• Mesomeric Effect (M): Present. The C=C double bond is conjugated with the C=O double bond of the acetyl group, allowing for resonance. The C=O group exhibits a -M effect.
• Hyperconjugation (H): Present. There are alpha-hydrogens on the methyl group attached to the double bond (at C2) and on the methyl group of the acetyl moiety (-COCH₃). These hydrogens are adjacent to sp² hybridized carbons and contribute to hyperconjugation. The methyl group at C6 also has alpha-hydrogens attached to a saturated carbon, which can contribute to hyperconjugation, although usually less significantly than those directly adjacent to pi systems. However, for the presence of the effect, it is considered.
  • Exhibits all three effects.

Summary: The compounds that show inductive, mesomeric, as well as hyperconjugation effects are:

1. Methoxybenzene (Anisole)
2. 3-Methylpent-3-en-2-one
3. 2-Isopropyl-1-nitrobenzene
4. 2-Allyl-1-nitrobenzene
5. 3-Methylanisole
6. 1-Acetyl-2,6-dimethylcyclohex-1-ene

Therefore, there are 6 such compounds.