CH 9-4: NMR-I Chemical Equivalence and Chemical Shift (1)Chemical Equivalence of Hydrogen atoms. The number of equivalent H atoms, or groups of H atoms corresponds to the number of “signals” in the NMR spectrum. (a)(b)(a)(b)

Chemical Equivalence = Number of Signals 2 signals 3 signals 1 signal 2 signals

(2) The NMR Spectrum: Chemical Shift Scale The “Chemical Shift” scale is defined as ppm, and ranges from ppm. (a)(b) (a) (b) (a) (b)

The “Chemical Shift” is a measure of how far a proton signal is relative to “zero” as defined by the TMS reference. “upfield”“downfield”

H-1 NMR Chemical Shift Data

Chemical Shift Data: 0 – 4.5 ppm Many protons give signals in the region from 0 – 4.5 ppm; not diagnostic for protons on specific functional groups.

The region from 4.5 – 13 ppm is very diagnostic for protons on specific functional groups. Chemical Shift Data: 4.5 – 13 ppm