Carbon compounds element abundance relative

Formally oxygen is also an A + 2 element. However, the natural abundance of the lsO isotope is only 0.2% of that of the main isotope ieO. That is why reliable calculation of the number of oxygen atoms based on the intensity of the isotopic peaks is hardly possible. Nevertheless, it is quite possible to estimate this number. Thus, if the intensity of the M + 2 peak in the mass spectrum of a sample with a low number of carbon atoms is higher than 0.5% relative to M+, this compound may contain one or more oxygen atoms. 

Carbon and its compounds occur widely, and the element is 14th in abundance. The most prevalent naturally occurring compounds are C02, living organisms, coal, natural gas, and petroleum. Relatively small amounts of the element are found in the graphite and diamond forms. 

The isotopic distributions of several elements commonly found in organic compounds are shown in Table 13.2. From the isotopic distributions, we see why the M -b 1 peak can be used to determine the number of carbon atoms in a compound It is because the contributions to the M + 1 peak by isotopes of H, O, and the halogens are very small or nonexistent. This formula does not work as well in predicting the number of carbon atoms in a nitrogen-containing compound because the natural abundance of is relatively high. 

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