Problem Set #2

Problem Set #2
Organic Chemistry c3443x
Fall '97

1. 2-Methylbutane has three different C-C bonds that can fragment upon homolysis. Draw the expected radicals for each homolysis product that are associated with the three pathways. Using delta H°_f values from Appendix I, which pathway would be expected to predominate.

2. Each hydrocarbon below contains no double or triple bonds and reacts with chlorine to give a monochlorinated product. Deduce the structure of each hydrocarbon and its monochlorinated product.

(a) C₈H₁₈ (b) C₈H₁₆ (c) C₈H₈

3. Using only dissociation ethalpies (DH°) given in Appendix II, calculate the enthalpy (delta H°) for each of the following steps in the bromination of ethane as well as for the overall process.

Overall process

Determine delta H° for the overall reaction using delta H°_f values from Appendix I and compare your results with the value calculated using dissociation enthalpies (they should be the same).

4. Calculate delta H°_f for the isobutyl radical (CH₃)₂CHCH₂• from the following data. Delta H°_comb (graphite per carbon) and hydrogen (H₂) are -94.05 and -57.80 kcal mol^-1, respectively. Delta H°_comb (CH₃)₂CHCH₃ is -632.77 kcal mol^-1. The dissociation enthalpy (DH°) for H₂ and the primary C-H bond in isobutane (CH₃)₂CHCH₂-H) is 104 and 101 kcal mol^-1, respectively.