NUCLEAR MAGNETIC RESONANCE 



91 



tinctive not of nitrogen alone, but of nitrogen in its particular sur- 

 roundings. These same surroundings might recur in several different 

 types of molecule, or might be confined to one. The formula of ethyl 

 alcohol may be written as CH3-CH2-OH. This compound presents 

 three proton-peaks, Fig. 7, separated by a few per cent of one gauss 

 when the big field is of the order of 10,000: they have been ascribed 

 to protons in the three "groups" CH3 and CH2 and OH. To identify a 

 group is to perform a process of chemical analysis, and this is a nascent 

 application of nuclear magnetic resonance. 



This is a good place to speak of the efficacy of nuclear resonance in 

 revealing the presence of chemical elements or of individual isotopes. 

 The proton is one of the easiest nuclei to discern in this way, largely 

 owing to its relatively high magnetic moment. It has been calculated 

 that 2-10^^ protons suffice to give a detectable "signal" by the induc- 



Fig. 7 — Breakup of the proton resonance peak of ethyl alcohol into three 

 peaks, each believed to arise from protons in distinctive 'groups within the 

 molecule. (Courtesy of M. E. Packard). 



