Stability of `pi`-bond in following alkenes in the increasing order is :
`underset("(I)")CH_(3)-CH=CH-CH_(3)" "underset("(II)")(CH_(3)-underset(CH_(3))underset(|)C=underset(CH_(3))underset(|)C-CH_(3))" "underset("(III)")(CH_(3)-underset(CH_(3))underset(|)C=CH_(2))"`
`underset("(IV)")(CH_(3)-underset(CH_(3))underset(|)C=CH-CH_(3))`

Options

A. `IltIIIltIVltII`
B. `IltIIltIIIltIV`
C. `IVltIIIltIIltI`
D. `IIltIIIltIVltI`

Answer

To determine the stability of the π-bond in the given alkenes, we will analyze each compound based on two main factors: the number of alpha hydrogen atoms and the degree of substitution of the double bond. More substituted alkenes are generally more stable due to hyperconjugation and the inductive effect.

Let's analyze each alkene:

1. **Alkene (I)**: CH₃-CH=CH-CH₃
- This alkene has a double bond between the second and third carbon atoms.
- The alpha carbons (adjacent to the double bond) are CH₃ groups, each contributing 3 hydrogen atoms.
- Total alpha hydrogens = 3 (from left CH₃) + 3 (from right CH₃) = 6 alpha hydrogens.
- Substitution: This is a monosubstituted alkene.

2. **Alkene (II)**: (CH₃)₂C=CH₂
- Here, we have a double bond between the second and third carbon atoms.
- The alpha carbon (adjacent to the double bond) is a tertiary carbon (two CH₃ groups).
- Total alpha hydrogens = 3 (from left CH₃) + 3 (from right CH₃) = 6 alpha hydrogens.
- Substitution: This is a trisubstituted alkene.

3. **Alkene (III)**: (CH₃)₂C=CH-CH₃
- The double bond is between the second and third carbon atoms.
- The alpha carbon is also a tertiary carbon.
- Total alpha hydrogens = 3 (from left CH₃) + 2 (from CH) + 3 (from right CH₃) = 8 alpha hydrogens.
- Substitution: This is a disubstituted alkene.

4. **Alkene (IV)**: (CH₃)₂C=CH-CH₂-CH₃
- The double bond is between the second and third carbon atoms.
- The alpha carbon is a secondary carbon.
- Total alpha hydrogens = 3 (from left CH₃) + 2 (from CH) + 2 (from right CH₂) = 7 alpha hydrogens.
- Substitution: This is also a disubstituted alkene.

Now, let's summarize the findings:

- Alkene (I): 6 alpha hydrogens, monosubstituted (least stable)
- Alkene (II): 6 alpha hydrogens, trisubstituted (most stable)
- Alkene (III): 8 alpha hydrogens, disubstituted (more stable than I but less than II)
- Alkene (IV): 7 alpha hydrogens, disubstituted (more stable than I but less than II)

Now, we can arrange the stability in increasing order:

1. Alkene (I) - least stable
2. Alkene (IV) - more stable than (I)
3. Alkene (III) - more stable than (IV)
4. Alkene (II) - most stable

Thus, the stability of the π-bond in the given alkenes in increasing order is:

**(I) < (IV) < (III) < (II)**