Molecular size was inferred from direct measurements of self-diffusion
for species resolved by 1H DOSY NMR (table
2 ). Often the sizes of oil oxidation products are estimated using size
exclusion chromatography in THF solvent, with polystyrene standards. In
contrast, DOSY provides self-diffusion coefficients (D) of multiple
species in solution resolved by 1H NMR.
DOSY measures the measured by mean-squared displacement (D), in one
direction (z), of a molecule undergoing Brownian motion, over time (t)
as z2 = 2Dt. D (in units of m2/s) is
obtained for multiple species simultaneously, replacing laborious
measurements with tracer reagents. Application of a linear magnetic
field gradient (G) allows detection of molecular translations (over
micrometers), see Figure S1 . D is used to reveal changes in
size. More massive molecules (oligomers) diffuse more slowly. DOSY plots
are expanded in the D dimension, leaving out the 1H
signal (at 7.25 ppm) from residual CHCl3 (in CDCl3),
with fast D = ca. 30 x 10-10 m2/s.