Chemistry Fundamental Principles of Organic Chemistry PMDC 2020
PMDC Verified Question 58 of 83
Generic formula of cycloalkane is:
A
\( \text{C}_n\text{H}_{2n+2} \)
B
\( \text{C}_n\text{H}_{2n} \)
C
\( \text{C}_n\text{H}_{2n-1} \)
D
\( \text{C}_n\text{H}_{2n-2} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: \( \text{C}_n\text{H}_{2n} \)
Concept:

The general formula connects the number of carbon atoms (n) to hydrogen atoms. Forming a ring from an open chain requires the removal of two hydrogen atoms to connect the ends.

Solution:

  • An open-chain alkane has the formula \( \text{C}_n\text{H}_{2n+2} \).


  • To form a single ring (a cycloalkane), two ends of the chain join together, expelling 2 hydrogen atoms.


  • Therefore, the formula becomes \( \text{C}_n\text{H}_{2n} \).


  • (Note: This is the same general formula as mono-alkenes).


Why other options are incorrect:

Option A is for straight-chain alkanes. Option D is for alkynes or dienes.

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