Limonene, mass spectrum

The peak at m/z 68 in the mass spectrum of limonene results from the molecule breaking in half as shown in Figure 9.14. 

El mass spectrum of limonene produced by retro Diels-Alder fragmentation. 

In the mass spectrum of limonene (Fig. 8.14), the intense peak at title = 68 corresponds to the diene... 

Limonene is a hydrocarbon found in the peels of lemons and contributes significantly to the smell of lemons. Limonene has a molecular ion peak at m/z= 136 in its mass spectrum, and it has two double bonds and one ring in its structure. What is the molecular formula of limonene ... 

The mass spectra of cycloalkenes show quite distinct molecular ion peaks. For many cycloalkenes, migration of bonds gives virtually identical mass spectra. Consequently, it may be impossible to locate the position of the double bond in a cycloalkene, particularly a cyclopentene or a cycloheptene. Cyclohexenes do have a characteristic fragmentation pattern that corresponds to a retro Diels-Alder reaction (Fig. 8.22). In the mass spectrum of the monoterpene limonene (Fig. 8.34), the intense peak at miz = 68 corresponds to the diene fragment arising from the retro Diels-Alder fragmentation. 

---