Chemistry Hydrocarbons DUHS 2024
PMDC Verified Question 7 of 65
The bond length between C-C in benzene is:
A
1.34Å
B
1.39Å
C
1.56Å
D
1.38Å
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: 1.39Å
Concept:

Because of resonance, the carbon-carbon bonds in benzene are intermediate in length and strength between a standard single bond and a standard double bond.

Solution:

  • A pure C-C single bond (alkane) has a length of 1.54 Å.


  • A pure C=C double bond (alkene) has a length of 1.34 Å.


  • In benzene, the pi electrons are completely delocalized over all six carbon atoms. This means every bond is functionally a "one-and-a-half" bond.


  • X-ray diffraction shows all six C-C bonds in benzene are exactly equal at 1.397 Å (often cited as roughly 1.39 Å).


Why other options are incorrect:

  • 1.34 Å is the length of an isolated double bond.


  • 1.54 Å (closest to 1.56 Å) is the length of an isolated single bond.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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