MCQ Detailed View

Alcohols are classified into primary, secondary, and tertiary based on the number of carbon atoms attached to the carbon bearing the hydroxyl (-OH) group. When alcohols undergo oxidation, their products depend on their class and the availability of a hydrogen atom on the carbon bonded to the -OH group.

A primary alcohol (R-CH₂OH) has two hydrogen atoms attached to the carbon bearing the hydroxyl group. When oxidized under controlled conditions with oxidizing agents like potassium dichromate (K₂Cr₂O₇) or pyridinium chlorochromate (PCC), it loses two hydrogen atoms—one from the hydroxyl group and one from the alpha carbon—to form an aldehyde (R-CHO). The oxidation process does not break the carbon skeleton, meaning the aldehyde produced has the same number of carbon atoms as the original alcohol.

For example:

CH3CH2OH  →[O]  CH3CHOCH₃CH₂OH \;\xrightarrow{[O]}\; CH₃CHOCH3CH2OH[O]CH3CHO

Here, ethanol (primary alcohol) oxidizes to acetaldehyde, maintaining the same two-carbon structure.

The other options are not correct:

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  Secondary alcohols (R₁-CHOH-R₂): Oxidize to ketones, not aldehydes.

  
  


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  Tertiary alcohols (R₁R₂R₃COH): Do not undergo oxidation easily because they lack a hydrogen atom on the carbon bearing the -OH group.

  
  


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  None of these: Incorrect, since primary alcohols fit the condition.

  
  

This reaction is a fundamental concept in organic chemistry, as it explains how aldehydes are synthesized from alcohols and highlights the relationship between functional groups during oxidation. It is also an important step in industrial processes, such as converting ethanol to acetaldehyde, which is a key raw material for many chemical products.