Chapter 16, Problem 16.15P

Interpretation Introduction

Interpretation:

The protons D–H are to be ranked in order from largest chemical shift to smallest.

Concept introduction:

A proton’s absorption peak is shifted downfield (i.e., to higher chemical shift) by nearby electronegative atoms. This downfield shift occurs because electronegative atoms are inductively electron withdrawing, so they remove electron density from the nearby proton. The proton is said to be deshielded, resulting in a higher signal frequency, and thus, a larger chemical shift. Magnetic anisotropy deshields hydrogen nuclei associated with simple alkenes and aldehydes. The inductive effect and magnetic anisotropy shifts the proton signal downfield leading to a higher chemical shift. The effects that cause deshielding are essentially additive. Deshielding effects fall off very rapidly with distance.