How many signals would you expect to find in the 1H NMR spectrum of each of the following...

How many signals would you expect to find in the 1H NMR spectrum of each of the following compounds?

(a) Vinyl bromide

(b) 1,1-Dibromoethene

(c) cis-1,2-Dibromoethene

(d) trans-1,2-Dibromoethene

(e) Allyl bromide

(f) 2-Methyl-2-butene

Sample Solution (a) Each proton of vinyl bromide is unique and has a chemical shift different from the other two. The least shielded proton is attached to the carbon that bears the bromine. The pair of protons at C-2 are diastereotopic with respect to each other; one is cis to bromine and the other is trans to bromine. There are three proton signals in the NMR spectrum of vinyl bromide. Their observed chemical shifts are as indicated.