In the ¹H NMR spectrum of bromoethane the methylene group is split into a quartet by the α and β nuclear spins of the protons on the neighboring methyl group. If the external magnetic field, B_∘, directs upward, which sequence of nuclear spins contributes to the second farthest peak down field within the spin-spin splitting pattern?

Question

Quizplus · Accepted Answer

The methylene protons in bromoethane are split into a quartet by the α and β protons on the neighboring methyl group. Since the external magnetic field is directed upward, the spin of the α proton will be oriented downward (↓) and the spin of the β proton will be oriented upward (↑). The quartet splitting pattern arises from the coupling of these two spins to the spin of the methylene protons. The second farthest peak downfield will be a peak with two adjacent spins oriented in opposite directions. This corresponds to the α and β protons, which can be represented as ↑↓ or ↓↑. The closest choice is B, which shows ↑↓↑. The other choices either have all spins oriented in the same direction (C) or have a sequence that is not physically possible (A, D and E).

In the 1H NMR Spectrum of Bromoethane the Methylene Group

In the ¹H NMR Spectrum of Bromoethane the Methylene Group