Chem 334 - Summer 1998 - Organic Chemistry I Dr. Carl C. Wamser

Chapter 3 Homework Answers - Alkanes. Reactions

Vollhardt & Schore, pp 101 - 105:
Problems 2c , 3 , 5 , 6 , 8 , 10 , 12 , 14 , 22

1. Hydrogen reacts with chlorine in a free radical chain mechanism to form HCl. Write out a complete mechanism, indicating the initiation, propagation, and termination steps. Calculate H for each of the steps and for the overall reaction.

overall reaction: H2 + Cl2 -----> 2 HCl H = -44 kcal/mol

initiation: Cl2 ---(heat or light)---> 2 Cl H = +58 kcal/mol

propagation (1): Cl + H2 -----> HCl + H H = +1 kcal/mol

propagation (2): H + Cl2 -----> HCl + Cl H = -45 kcal/mol

termination: H + Cl -----> HCl H = -103 kcal/mol

or Cl + Cl -----> Cl2 H = -58 kcal/mol

or H + H -----> H2 H = -104 kcal/mol

2. Fluorine is so reactive with alkanes that the rate is explosive and the products show almost no selectivity. Predict the monofluorination products expected from 2-methylpentane. Give their structures, correct IUPAC names, and the expected proportions of each, based on the selectivity data given in Table 3-5 in your text.