Which of the protons in the following molecule appear furthest downfield in the ¹H NMR spectrum?

Question

Quizplus · Accepted Answer

The proton in the iii position appears furthest downfield because it is directly attached to the phosphorus atom (P11) which has a strong electron-withdrawing effect. This causes the surrounding atoms to become deshielded and therefore have a higher chemical shift. The other protons are further away from the phosphorus atom and are therefore less affected by its electron-withdrawing effect.

Which of the Protons in the Following Molecule Appear Furthest