Question

Which of the following compounds has the most deshielded protons? CH3Cl CH3I CH3Br CH4

Answer 1

Deshielding is the effect of withdrawal of electron density from a specific atom. Electronegative atoms like F, Cl, O, N, Br and I generally deshield the nearby atoms. When an atom is deshielded, it interacts more with the local magnetic field resulting in higher chemical shift compared to a shielded atom.

Between CH₃Cl, CH₃I, CH₃Br and CH₄, the first three molecules contain an electronegative atom. Hence, CH₄ has the most shielded protons and will result in a small value of chemical shift.

The question asks for the most deshielded protons.

Since deshielding in our molecules are being caused by the electronegaative atoms, Cl, Br and I, the more electronegative the atom is, more is the deshielding. Since Cl is more electronegative than I and Br, the protons of CH₃Cl will be the most deshielded among the given molecules.

Note the order of deshielding from most to least deshielded will be .

Hence, the correct choice is CH₃Cl.