# How do I recognize vinyl cations? How are they made?

I am having trouble understanding this concept. Vinyl cation was a test question in my organic chem class. The professor mentioned that a vinyl cation cannot make the leaving group leave and that it must be on the double bond for it to be vinyl. The questioned asked as following:

Which is the best to make the vinyl cation?

a) $$\ce{C-C#C - H+ ->}$$

b) C-C=C --KOH-->

    |
Cl


c) C-C=C --H+-->

    |
OH


d) a+c

Addition of $\ce{HX}$ to $\ce{R1-C#C-R2}$ is assumed to proceed via cyclic intermediate in which the proton bridges the sp centres.
Vinyl cations can be formed from alkenes, supposed they are substituted with a super leaving group, such as $\ce{-OSO2CF3}$ (OTf, trifluoromethanesulfonate, triflate) or $\ce{-OSO2(CF2)3CF3}$ ((ONf, nonafluorobutanesulfonate, nonaflate).