Finally, let's consider the ozonolysis of limonene, 13. Limonene contains an exocyclic and an endocyclic double bond. The exocyclic double bond accounts for the two products of ozonolysis, 25 and 26. The presence of formaldehyde 26 means that one of the double bonds in limonene is monosubstituted, i.e., formaldehyde correlates with the aldehyde group of 25, or one of the double bonds is 1,1-disubstituted, i. e., correlation with one of the keto groups in 25.

There are three permutations by which 24 can be reassembled to form an endocyclic double bond. The aldehyde group and the righthand keto group in 25 lead to limonene 24, a 6-membered ring. The other two permutations lead to cyclopentene 27 and cyclobutene 28. It is impossible to decide without more information. Try this problem. ---> Index