Shoolery's rule

Shoolery's rule, which is named after James Nelson Shoolery, is a good approximation of the chemical shift δ of methylene groups in proton nuclear magnetic resonance. We can calculate shift of the CH2 protons in a A–CH2–B structure using the formula
 * $$\delta = 0.23\,\mathrm{ppm} + S_\mathrm{A} + S_\mathrm{B}$$

where 0.23 ppm is the chemical shift of methane and the empirical adjustments S are based on the identities of the A and B groups:

Shoolery's rule is a particular instance of a general class of rules of the form
 * $$\delta = b_0 + \sum_i z_i$$,

with two substituents on methylene resulting in two parameters $$S_A$$ and $$S_B$$.