Organic Chemistry

John McMurry

ISBN #9781305080485

9th Edition

1,986 Questions

21,829 Students Helped

Homework Questions

Summary

Learning Objectives

Key Concepts

Example Problems

Explanations

Common Mistakes

Summary

Pericyclic reactions are a distinct class of concerted reactions that occur via cyclic transition states, with no intermediates. Their stereochemistry is governed by the symmetry of frontier molecular orbitals and can be accurately predicted using the Woodward–Hoffmann rules and mnemonics like TECA. Understanding the differences between thermal and photochemical conditions is key for anticipating outcomes in electrocyclic, cycloaddition, and sigmatropic processes, making these principles fundamental for both synthetic organic chemistry and understanding natural processes such as vitamin D production.

Learning Objectives

Key Concepts

CONCEPT

DEFINITION

Acid–Base Chemistry

The study of acids and bases using both the Brønsted–Lowry (proton-donating/accepting) and Lewis (electron pair accepting/donating) frameworks, including quantification via pKa values, which together explain chemical reactivity in organic molecules. •

Example Problems

Example 1

Look at Figure $30-1,$ and tell which molecular orbital is the HOMO and which is the LUMO for both ground and excited states of ethylene and 1,3 -butadiene.

Example 2

Draw the products you would expect from conrotatory and disrotatory cyclizations of $(2 Z, 4 Z, 6 Z)-2,4,6$ -octatriene. Which of the two paths would you expect the thermal reaction to follow?

Example 3

trans-3,4-Dimethylcyclobutene can open by two conrotatory paths to give either $(2 E, 4 E)-2,4$ -hexadiene or $(2 Z, 4 Z)-2,4$ -hexadiene. Explain why both products are symmetry-allowed, and then account for the fact that only the $2 E, 4 E$ isomer is obtained in practice.

Example 4

What product would you expect to obtain from the photochemical cyclization of $(2 E, 4 Z, 6 E)-2,4,6$ -octatriene? Of $(2 E, 4 Z, 6 Z)-2,4,6$ -octatriene?

Example 5

What stereochemistry would you expect for the product of the Diels-Alder reaction between $(2 E, 4 E)-2,4$ -hexadiene and ethylene? What stereochemistry would you expect if $(2 E, 4 Z)-2,4$ -hexadiene were used instead?