Propylbenzene, mass spectrum

FIGURE 13 43 The mass spectrum of propylbenzene The most intense peak is... 

Repeat your analysis for n-propylbenzene. (Compare geometries of 1-propylbenzene radical cation and 1-propylbenzene.) Where would you expect a strong peak in the mass spectrum Identify the ion responsible. 

Fig. 6.14. El mass spectrum of n-propylbenzene. The molecular ion peak and the primary fragment ion have significant intensity, whereas low-mass fragments are less abundant. Spectrum used by permission of NIST. NIST 2002.

Exercise 9-47 The mass spectrum of propylbenzene has a prominent peak at mass number 92. With (3,3,3-trideuteriopropyl)benzene, this peak shifts to 93. Write a likely mechanism for breakdown of propylbenzene to give a fragment of mass number 92. 

If we have the mass spectrum of a molecule containing an aromatic ring, then we should expect to find a peak from a very stable ion, the benzyl ion, PhCH2, provided the structure permitted this ion to form. An unsubstituted benzyl peak is found at m/z 91 substitution will obviously change the mass of the ion. Formation of a benzyl ion is shown in the next spectrum. Figure 2.4, which shows the mass spectrum of propylbenzene, PhCH2CH2CH3. 

The mass spectrum of propylbenzene. The most Intense peak Is... 

Mass spectra for l-bromo-4-propylbenzene and (3-bromopropyl)benzene are shown in Figure 13.45. Match each spectrum to the appropriate compound. Write a structure for the ion that corresponds to the base peak in each spectrum. 

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