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Answers:

option A

Reasoning:

Since both molecules have the same expected number of signals at approximately the same expected positions in the spectrum, it becomes necessary to look at the fine structure of the signals - as well as their respective relative intensities - if we attempt to assign the proper molecule to the spectrum.
  • The two methyl groups -CH2-CH2- would give rise to two tripletts in the spectrum, while
  • the >CH-CH3 group would generate a doublet and a quartet .
Molecule Equivalent protons d [ppm] (expected) Integral (expected) Multiplicity (expected)
a) CH3-CHBr-CO-CH3 -CHBr-CH3
-CO-CH3
-CHBr-
0.6 ... 1.9
1.7 ... 2.7
2.8 ... 5.8
3
3
1
2
1
4
c) CH2Br-CH2-CO-CH3 -CO-CH3
-CH2Br-CH2-CO-
-CH2Br
1.7 ... 2.7
1.9 ... 3.2
2.4 ... 4.7
3
2
2
1
3
3

(If you had problems with this type of question, then you might want to go back and work through the section on spin-spin coupling once more.)

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