Question 22.10: Draw all the isomers of the molecule C2H2Cl2 in which two of...
Draw all the isomers of the molecule C_{2}H_{2}Cl_{2} in which two of the H atoms of ethylene are replaced by Cl atoms.
1. Write the structure for ethylene.
\begin{array}{r c}\begin{matrix} \ H\ _{_{\diagdown} }\quad\quad\quad _{_\diagup }H \\C=C\\ H\ ^{^\diagup }\quad \quad \ \ ^{^\diagdown }H \end{matrix} \end{array}2. Substitute two Cl atoms for the two H atoms on the right.
\begin{array}{r c}\begin{matrix} \ H\ _{_{\diagdown} }\quad\quad\quad _{_\diagup }Cl \\C=C\\ H\ ^{^\diagup }\quad \quad \ \ ^{^\diagdown }Cl \end{matrix} \end{array}Substituting two Cl atoms for the two H atoms on the left gives the identical structure just written.
3. Substitute Cl atoms for the two H atoms at the top (1 H atom per C atom).
Substituting two Cl atoms for the two H atoms on the bottom gives the identical structure.
4. Substitute a Cl atom for the H atom on the top right and the other Cl atom for the H atom on the bottom left.
These are all the isomers that can be drawn.
END POINT
1. The first structure does not show any cis-trans isomerism because the two Cl atoms are bonded to the same C atom.
2. The second structure is the cis-isomer.
3. The third structure is the trans-isomer.