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GATE 2021 CY – Question 33

Organic Chemistry · Experimental Techniques in Organic Chemistry: Optical rotation (polarimetry). Application of various chromatographic techniques such as thin-layer, column, HPLC and GC. Applications of UV-visible, IR, NMR spectroscopy and Mass spectrometry in the structural determination of organic molecules. · 1 mark · Numerical answer

The number of $^1H$ NMR signals of the illustrated compound at 25 °C in $CDCl_3$ is ______.

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Correct answer: 3 to 3

Explanation

A mirror symmetry through Br and the opposite acetyl group exchanges the two remaining aromatic hydrogens, so they give one aromatic signal. It also exchanges the two acetyl groups adjacent to Br, giving one methyl signal for those six hydrogens. The opposite acetyl methyl gives a second methyl signal.

Thus there are **3 chemical shifts**, irrespective of multiplicity.