Chapter 8, Problem 8.114MP

Just as individual bonds in a molecule are often polar, molecules as a whole are also often polar because of the netsum of individual bond polarities. There are three possiblestructures for substances with the formula ${\text{C}}_{\text{2}}{\text{H}}_{\text{2}}{\text{Cl}}_{\text{2}}$ , two ofwhich are polar overall and one of which is not.
(a) Draw the three possible structures for ${\text{C}}_{\text{2}}{\text{H}}_{\text{2}}{\text{Cl}}_{\text{2}}$ , predictan overall shape for each, and explain how they differ.
(b) Which of the three structures is non polar, and which two are polar? Explain.
(c) Two of the three structures can be inter converted by aprocess called cis−trans isomerization, in which rotation around the central carbon—carbon bond takes place when the molecules are irradiated with ultraviolet light. If light with a wavelength of approximately 200 nm is required for isomerization, how much energy in kJ/mol is involved?
(d) Sketch the orbitals involved in the central carbon-carbon bond, and explain why so much energy is necessary for bond rotation to occur.