Question

\(\mathrm{H}_{2} \mathrm{C}=\mathrm{CH}-\mathrm{C}^{\mathrm{O}} \sum_{\mathrm{H}}^{\mathrm{CH}_{3} \mathrm{OH}}{\mathrm{dryHCl}}(\mathrm{A}) \stackrel{\mathrm{dil.KMnO}_{4}}{\longrightarrow}(\mathrm{B}) \stackrel{\mathrm{dil} \cdot \mathrm{HCl}}{\longrightarrow}(\mathrm{C})\) The structure of (C) is (a) \(\mathrm{H}_{2} \mathrm{C}=\mathrm{CHCH}_{2} \mathrm{OH}\) (b) \(\mathrm{HOCH}_{2}-\mathrm{CHOH}-\mathrm{CHO}\) (c) \(\mathrm{OHC}-\mathrm{CH}_{2}-\mathrm{COOH}\) (d) \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{COOH}\)

Short answer

Answer: The structure of compound (C) is \(\mathrm{HOCH}_{2}-\mathrm{CHOH}-\mathrm{CHO}\).

Step-by-step solution

Initial Compound (A)

The initial compound (A) has this formula: \(\mathrm{H}_{2}\mathrm{C}=\mathrm{CH}-\mathrm{C}^{\mathrm{O}}\). This indicates that it is an aldehyde.

Reduction of Aldehyde with Dry HCl

In this step, the aldehyde group in compound (A) gets reduced by dry HCl to form compound (B). The aldehyde group is transformed into an alcohol group. Thus, the structure of compound (B) becomes: \(\mathrm{H}_{2}\mathrm{C}=\mathrm{CH}-\mathrm{CH}_{2}\mathrm{OH}\).

Oxidation with Dilute KMnO4

Now, we need to oxidize compound (B) with dilute \(\mathrm{KMnO}_{4}\). In this reaction, the carbon-carbon double bond will be oxidized to form two alcohol groups, so our intermediate product would be: \(\mathrm{HOCH}_{2}-\mathrm{CHOH}-\mathrm{CH}_{2}\mathrm{OH}\).

Acidification with Dilute HCl

The final step involves acidification with dilute HCl. This will convert any alcohols adjacent to a carbonyl group into a ketone or an aldehyde. In our case, the intermediate product formed in Step 3 has an alcohol group adjacent to another alcohol group. Upon acidification, the terminal alcohol group gets oxidized to an aldehyde group: \(\mathrm{HOCH}_{2}-\mathrm{CHOH}-\mathrm{CHO}\).

Identify the Structure of Compound (C)

Now that we have the structure of the final product after the sequence of reactions, we can compare it to the given options: (a) \(\mathrm{H}_{2}\mathrm{C}=\mathrm{CHCH}_{2}\mathrm{OH}\) (b) \(\mathrm{HOCH}_{2}-\mathrm{CHOH}-\mathrm{CHO}\) (c) \(\mathrm{OHC}-\mathrm{CH}_{2}-\mathrm{COOH}\) (d) \(\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{COOH}\) Our final product is the same as option (b), \(\mathrm{HOCH}_{2}-\mathrm{CHOH}-\mathrm{CHO}\). Therefore, option (b) is the correct answer for the structure of compound (C).

Key concepts

Aldehyde Reduction

Aldehyde reduction is a crucial process in organic chemistry. It's a reaction where an aldehyde group is transformed into an alcohol group. This is achieved through the addition of hydrogen (reduction).
In our exercise, the compound undergoes reduction by reacting with dry HCl. Although HCl is typically known as an acid, in some creative reactions, it acts indirectly as a reducing agent.

• In this setting, the aldehyde group in the compound i.e., (−CHO), changes to a hydroxyl group (−CH₂OH),
• turning the carbon-oxygen double bond into a single bond.

This conversion is essential and is often a precursor step to more complex organic transformations. It allows further adjustments of the molecule, opening new opportunities for desired chemical structure modifications.

Oxidation Reactions

Oxidation reactions in organic chemistry often involve an increase in the oxidation state of a molecule. This can mean the addition of oxygen atoms or the removal of hydrogen atoms.
In this exercise, the compound post-reduction undergoes such oxidation through a reaction with dilute potassium permanganate ( KMnO₄).

• The carbon-carbon double bond, crucial to the initial structure, is oxidized,
• and each carbon in the double bond forms an additional alcohol group with hydroxyl (-OH).

For instance, the structure transforms the double-bonded carbon atoms into diol configurations:

(−CHOH). Thus, producing a compound with primary and secondary alcohol groups is key to setting the stage for later reactions.

Acidification with HCl

The role of acidification in organic reactions is to alter functional groups. Through acid-catalyzed mechanisms, it can turn alcohols into aldehydes or ketones.
In the final part of our exercise, the compound formed from oxidation undergoes acidification with dilute hydrochloric acid (HCl). The focus here is on the alcohol groups connected to the molecule, close to carbonyl locations.

• When the molecule is exposed to HCl, the terminal alcohol group adjacent to another alcohol,
• is further oxidized, resulting in an aldehyde group (-CHO).

This selective oxidation leads to the final product of the reaction sequence, demonstrating the importance of acidification in finalizing organic synthesis reactions.