Chem 1a Review

Chemistry 1A Final Exam Review

This is an example of a set of challenging problems that is meant to tie this semester’s material together. We suggest you work through it prior to the review session, and practice making your own questions for review.

Ferrocene is a famous organometallic complex with the molecular formula Fe(C5H5)2. Two cyclopentadienyl rings are bound through their pi bonds to the metal.

a) The structure above has two cyclopentadienyl rings. Cyclopentadiene (C5H6) is shown below. What is the hybridization on each carbon atom? Indicate the approximate bond angles of the carbons.

b) The above cyclopentadiene molecule is neutral; however, the molecule that bonds to the metal is negative and is called a cyclopentadienyl anion (C5H5-), where a lone pair of electrons is present on one of the carbons. Using the negatively charged structure below draw all resonance structures for a cyclopentadienyl anion (Hint: There are 5 total!). Based on the resonance structures you have drawn, what would you expect the hybridization and bond angle of the carbon atoms to be now (Hint: Think about the equivalence of the resonance structures)?

c) Cyclopentadiene is not fully soluble in water. Using your knowledge of intermolecular forces, give an explanation for why this is true.

d) The Ks value for liquid cyclopentadiene in water is 0.1 M. Write the Ks expression for this equilibrium, being sure to indicate the state of the substance(s) in the Ks expression. Calculate the molarity of cyclopentadiene in a saturated cyclopentadiene solution using your expression.

e) To become the cyclopentadienyl anion, cyclopentadiene loses one proton. The pKa of this proton is 16. Knowing this pKa, write an equilibrium expression for the deprotonation of cyclopentadiene, and determine the equilibrium constant

f) With a saturated solution of cyclopentadiene, how much cyclopentadienyl anion is present at equilibrium (give your answer in moles and...