Which of the following functional groups has the most deshielded proton and would be predicted to show an NMR signal that is the farthest downfield?

A) benzylic - H
B) allylic - H
C) aldehyde - H
D) aromatic - H
E) acetylenic - H

Deshielded Proton

A proton in an NMR spectrum that appears at lower field due to its electron cloud being less shielded from external magnetic fields, often indicating an electron-withdrawing group nearby.

Farthest Downfield

In NMR spectroscopy, refers to the signal appearing at the lowest field strength, typically associated with environments experiencing the greatest deshielding.