A 1 Elements Carbon and Nitrogen

The three A -I- 1 elements in Table 2.1 are hydrogen, carbon, and nitrogen, but the H/ H ratio is so low that we shall consider hydrogen to be an A element. Each element exhibits its isotopic abundances independently thus the carbon atom in the CHjBr molecule of Unknown 2.2 contributes 1.1% of the intensity of the m/z 94 peak ( CH3 Br ) to the mjz 95 peak ( CHj Br ), and of the tn/z 96 ( CHj Br ) to the 97 ( CHj Br ). Unknown 2.3, which contains no A -I- 1 elements, shows [m/z 65]/[m/z 64] close to that expected for one carbon (but actually due to and that gives us 

In Unknown 2.4, calculate [after checking for A + 2 elements] the maximum number of carbon atoms in the ions of m/z 43 and 58. The results indicate that m/z 43 peak is formed from the m/z 58 by the loss of what group  

Note that many small peaks in Unknown 2.4 were relatively unimportant for deriving its structure, such as peaks which can be formed from abundant peaks by the loss of hydrogen or which represent doubly charged ions. In other unknowns of this book, unimportant peaks will often be omitted. For Unknown 2.5, find the elemental formula of the molecular ion this is the largest ( base ) peak in the spectrum, indicating high stability. 

Double C-13. The Unknown 2.5 spectrum also contains a minor, but important, peak at m/z 80 of 0.2% intensity. Assigning this as the 0 contribution of one 0 atom in m/z 78 would mean that the latter contains no more than five carbon atoms, whereas the m/z 79 abundance indicates six. The peak at m/z 80 actually arises from ions containing two atoms and four atoms. 

The abundance of such (A + 2) ions relative to the A ion depends on the number of carbon atoms, just as [(A + 1) ]/[A ] does these abundances are also tabulated in Table 2.2. 

---