Illustrated Glossary of Organic Chemistry

Natural abundance: The relative amount of the isotopes of an element, as it occurs in nature. Influences intensity of signals in mass spectrometry and NMR spectroscopy (among other things).

Relative Abundance of Some Isotopes Important in Organic Chemistry
Isotopes not listed are present only in negligible amounts.
Element
   
Isotope (Natural Abundance)
   
Isotope (Natural Abundance)
   
Isotope (Natural Abundance)
Hydrogen
1H (99.985%)
2H (0.015%)

Carbon
12C (98.893%)
13C (1.107%)

Nitrogen
14N (99.634%)
15N (0.366%)

Oxygen
16O (99.759%)
17O (0.037%)
18O (0.204%)
Fluorine
19F (100%)



Sulfur
32S (95.0%)
33S (0.76%)
34S (4.22%)
Chlorine
35Cl (75.77%)


37Cl (24.23%)
Bromine
79Br (50.69%)


81Br (49.31%)
Iodine
127I (100%)