The values of this quantity can span a large range of about 800 in fluorine-19 NMR, far larger than the generally single-digit values for proton NMR. For 10 points each:
[10e] Name this quantity measured in ppm that represents the difference in the resonant frequency of a nucleus compared to that of a standard in NMR.
ANSWER: chemical shift
[10h] Inconsistencies in chemical shifts in fluorine-19 NMR were linked to interactions of this standard with various solvents. In fluorine-19 NMR, a chemical shift of 0 is assigned to the pure form of this ozone-depleting compound.
ANSWER: trichloro•fluoro•methane [or fluoro•trichloro•methane; or CCl3F; or CFCl3; accept R-11, freon-11, or CFC-11; reject partial answers]
[10m] Fluorine-19 NMR’s detection of a single fluorine environment for phosphorus pentafluoride, without separate axial and equatorial ones, led to the discovery of this mechanism of rapid isomerization of trigonal bipyramidal compounds.
ANSWER: Berry pseudorotation [or Berry mechanism; prompt on pseudorotation; reject answers containing just “rotation”]
<Gerhardt Hinkle, Chemistry>