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Reading Assignment: Heats of Formation and Heats of Hydrogenation

1. Read Degree (Elements) of Unsaturation. What is the molecular formula of Prozac? Draw its structure? Confirm its degree of unsaturation by computation (show work). Draw an acyclic compound having the same formula as Prozac (there are many). Does it have the same number of degrees of unsaturation?

2. a) Determine the heat of formation of 3-methyl-1-pentene. Use the heat of formation tables to determine typical heats of hydrogenation for monosubstituted alkenes and to determine the heat of formation of the the reduction product of 3-methyl-1-pentene. Show work.

b) Calculate the heat of hydrogenation of (E)-and (Z)-3-methyl-2-pentene. Show work.

c) Use a diagram to illustrate that the difference in the heat of hydrogenation of the two geometrical isomers in 2b is equal to the difference in their heats of formation. Which isomer is more stable based upon the heats of formation? Why?

d) There is only one monosubstituted alkene having the carbon skeleton of the (E)-and (Z)- isomers in 2b. What is its structure? Assuming that ΔG^o = ΔH^o, which of the three isomeric alkenes would dominate in an equilibrium mixture? How much heat is liberated in the isomerization of the monosubstituted alkene to the (E)-isomer? Show work. Add the monosubstituted alkene to your diagram in 2c and illustrate the heat of isomerization.

3. The major product B from free radical monobromination of alkane A (C₆H₁₄) readily reacts with water to form C, C₆H₁₄O. Treatment of bromide B with KOH in ethanol produces two, and only two, compounds, D and E. Compound D liberates 1.6 kcal/mol more heat upon hydrogenation to A than does E. What are the structures A-E? What is the heat of isomerization of D to E? Illustrate and explain. [Hint: What are the structures possible for A?]

K. B. Wiberg

5. Two stereoisomers, A and B, absorb one equivalent of hydrogen upon catalytic hydrogenation to form cyclooctane. Compound A, which is capable of resolution, liberates 34.5 kcal/mol of heat while B liberates 24.3 kcal/mol of heat.
a) What are the structures of A and B ?
b) What are the heats of formation of A and B ?
c) What is the difference in strain energy between A and B ?
d) What is the difference in the heat of combustion between A and B?
e) Why is A capable of resolution?