American Chemical Society 37 th Middle Atlantic Regional Meeting

1. American Chemical Society37th Middle Atlantic Regional Meeting MARM 2005 May 25, 2005 Busch Campus, Rutgers University

2. Abstract The structural features inherent in acyclic monoterpenes that follow the isoprene rule often lead to unique sets of ozonolysis products from which their structures, excluding stereochemistry, can be determined from molecular formulas only. Three examples show how students may elucidate the structures of these compounds by analysis of the oxidative and reductive workup products. The complete problem set contains 50 problems.

3. Introduction The molecular formula of a C10 hydrocarbon and the molecular formulas of its products of ozonolysis are provided. The hydrocarbon follows the isoprene rule. From this data, students determine the structure of the hydrocarbon. Some problems are solvable from the reductive workup products and some from the oxidative workup products. Other problems require the products of both workups for their solutions.

4. Methodology • The reductive workup of an ozonide invariably produces two carbonyl groups from a double bond and two carboxylic acids from a triple bond. These results lead to the following information from molecular formulas. • Reductive Workup (R) • The number of degrees of unsaturation • The number of triple bonds (tb) in the reactant • The number of p bonds (p) in the reactant • The number of double bonds (db) in the reactant • The number of rings (r) in the reactant

5. The presence of CH2O proves the presence of a terminal alkene in the reactant. • The presence of CH2O2 proves the presence of a terminal alkyne in the reactant. • Oxidative Workup (O) • Excluding CH2O, a one-oxygen atom difference between an oxidative and reductive product’s formula indicates an aldehyde-acid pair (e.g., a C6H12O aldehyde (R) becomes a C6H12O2 acid (O). • Any ketone isolated in the reductive workup is also isolated in the oxidative workup (e.g., C4H8O remains C4H8O).

6. Any acid isolated in the reductive workup is also isolated in the oxidative workup (e.g., C9H18O2 remains C9H18O2). • A dialdehyde in the reductive workup becomes a diacid in the oxidative workup as evidenced by a two-oxygen atom increase in the diacid (O2 to O4); a ketoaldehyde becomes a ketoacid (O2 to O3), an aldehyde-acid becomes a diacid (O3 to O4), etc.

7. Example 1 Structure of a Triene Hydrocarbon (HC) from its Reductive Workup Products Determine the structure of a C10H16 hydrocarbon that follows the isoprene rule and yields CH2O, C3H6O and 2 C3H4O2 upon ozonolysis by a reductive workup.

8. Structural features in red are determined from the molecular formulas. • Asymmetry in the template makes the C3H6O compound acetone, which arises from a C2-C3 db. • The other products must arise from db’s as shown in the template.

9. Example 2 Structure of a Diene Hydrocarbon (HC) from its Oxidative Workup Product Determine the structure of a C10H18 hydrocarbon that follows the isoprene rule and yields C2H2O2, C4H8O and C4H8O2 upon ozonolysis by an oxidative workup.

10. The three products require two multiple bonds, which must both be db’s because p + r = 2. • The db’s must be placed as shown on the template to give a four-carbon acid and a four-carbon ketone. • Structural features in red are determined from the molecular formulas.

11. Example 3 Structure of a Diene Hydrocarbon (HC) from its Reductive and Oxidative Workup Products Determine the structure of a C10H16 hydrocarbon that follows the isoprene rule and yields the ozonolysis products shown below.

12. Structural features in red are determined from the molecular formulas. • The tb must be placed on the template as shown to account for the four-carbon acid (R). • The db must be placed on the template as shown to account for the five-carbon diacid (O).

13. Limitations • Of 66 compounds, 16 in the series give two solutions. • Neither E/Z nor R/S stereochemistry can be determined by ozonolysis.

14. Conclusions • The structures of monoterpenes (enes, ynes, di- and trienes, and enynes) that follow the isoprene rule can be determined from their molecular formulas and those of their products of ozonolysis. • The fifty problems vary in difficulty, affording instructors of beginning organic or qualitative organic analysis courses a set of degradation problems that complement spectral and synthetic problems in engaging students to apply their knowledge and enhance their reasoning skills while solving challenging problems.

15. Notes 1. The complete problem set will be published as a supplement in J. Chem. Educ., in press. 2. The author’s email address is rgross@pgcc.edu.