(Originais Teachy 2023) - Question Hard of Chemistry

Consider two geometric isomeric compounds, A and B, with the molecular formula C3H6Cl2. Both have a carbon-carbon double bond, and in A, the two chlorine atoms are on the same side of the double bond, while in B, they are on opposite sides. Proton nuclear magnetic resonance spectroscopy (1H NMR) analysis showed that A has two distinct signals in the spectrum, while B has only one signal. Considering the information provided and the concepts of geometric isomerism, explain why A has two signals in the 1H NMR spectrum, while B has only one signal. Additionally, discuss the practical implication of these differences in the context of the development of new drugs that make use of Heck cross-coupling reactions, which are sensitive to geometric isomerism.