Question

Stilbene $\left(PhCH = CHPh\right)$ can exist in two diastereomeric forms $X$ , $Y$ and $X$ is found to be more soluble in water than $Y$ . Predict which of the following statement is correct?

• A. $X$ is trans isomer
• B. Stability of $X>$ Stability of $Y$
• C. Melting point of $X>$ melting point of $Y$
• D. Boiling point of $X>$ boiling point of $Y$

Answer 1

Answer: (D)

The stilbene exhibits cis-trans isomerism and the dipole moment of cis isomer is greater than trans isomer.

Cis form is more polar than trans form, hence, it has more boiling point.
$\uparrow\text{polarity}$
$\uparrow\text{solubility}$
$\uparrow\text{Boiling} \, \text{Point}$
More polar compound is more soluble in water. Hence, X is cis and Y is trans isomer. Close packing molecules have more melting point. Hence, the trans isomer has more melting point.