Abstract 13 C labelling has been used to study isoquinoline molecular ions undergoing breakdown by HCN elimination in a mass spectrometer. For otherwise stable ions caused to fragment by collisional activation, there is no skeletal rearrangement prior to HCN loss. Of the ions formed by 70 eV electron impact, 69% of those which fragment in the ion source by HCN loss retain their structural integrity, as do 44% of the metastable ions. Of the ions that ...
