Chemistry Industrial Chemistry PMDC Conceptual Practice
PMDC Verified Question 28 of 41
An auxochrome fails to deepen the color of a chromogen if it is substituted at which position relative to the chromophore?
A
Ortho position
B
Meta position
C
Para position
D
Both ortho and para positions
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Meta position
Concept:

Auxochromes deepen color (bathochromic shift) by donating or withdrawing electron density via resonance into the conjugated chromophoric \(\pi\)-system.

Formula / Reaction:

Qualitative concept / No formula required.

Solution:

  • Resonance delocalization between electron-donating auxochromes (e.g., \(-\text{NH}_2\), \(-\text{OH}\)) and electron-accepting chromophores operates efficiently only at ortho and para positions.


  • At the meta position, resonance interaction is electronically isolated, meaning the auxochrome cannot effectively extend conjugation or induce a significant bathochromic shift.


Why other options are incorrect:

  • Ortho and Para positions: Enable direct quinoid-type resonance delocalization, maximizing the bathochromic color-deepening effect.


  • Option D: Contradicts resonance stabilization theory.

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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