Question

"Which of the following isomeric dibromopropanes has only a single peak in its proton NMR spectrum?

A. 1.1-dibromopropane
B. 1,3-dibromopropane
C. 1,2-dibromopropane
D. 2,2-dibromopropane"

Answer 1

D. 2,2-dibromopropane

In 2,2-dibromopropane, the two bromine atoms are attached to the same carbon atom, which means that the two protons on that carbon are chemically equivalent and will give rise to a single peak in the proton NMR spectrum.

In contrast, the other isomeric dibromopropanes have two different sets of protons due to the different locations of the bromine atoms, so they will give rise to multiple peaks in the proton NMR spectrum.