Translational energy release and stereochemistry of steroids. VII—the loss of angular methyl groups after the dehydration of molecular ions of cholesterol and related C(5)‐unsaturated 3β‐hydroxy steroids

The translational energy, T , released during the loss of the angular 18‐ and 19‐methyl groups both from metastable molecular ions and metastable [M  H 2 O] + and [M  2H 2 O] + ions, in C(5)‐unsaturated mono‐and di‐hydroxy steroids, as well as in their 19‐nor and deuterated analogues bearing the label in the 19‐methyl group, has been measured. It was found that, while the T values for the 19‐CH 3 loss, following the dehydration of the molecular ions, are increased substantially when compared to those for the same loss from the molecular ions, the T values for the 18‐CH 3 loss are increased much more moderately. Nevertheless, the amounts of translational energy released in the [M  H 2 O] + ˙  18‐CH 3 ˙ and [M  2 H 2 O] + ˙  18‐CH 3 ˙ transitions are still higher than those found for the respective 19‐methyl loss, in accordance with the general rule established recently.