It is concluded that the trifluoroacetic acid bornyl ether is an intermediate of the alpha-pinene isomerization process. Schemes for the synchronous reactions of bornultrifluoroacetate formation from alpha-pinen and isobornyl ether formation from camphene are proposed. It is states that the decomposition of ethers in acid medium proceeds via the mechanisms E1 and E2 for endo- and exa-isomer respecitvely. The results found from these experiments allow to generalize the mechanism of bicyclic monoterpenes isomerization in the presence of protonic acids.