Alkene 7:
In the scheme above, hydrogen of HCl is distinguished from the hydrogen of hydride [H-]. The hydride migration mechanism places a green hydrogen at C3 of 4a. On the other hand, the formation of the alkene 6 causes the formation of H-Cl in the presence of H-Cl. Now, both carbocations 5a and 5b will be formed as will their products 4a and 4b, respectively. Unfortunately, red and green protons are not available. Nonetheless, there are different types of protons. Think about how an experiment using hydrogen and deuterium as red and green hydrogens can give information about the mechanism.