Soluções e Tautomeria

Prévia do material em texto

Chapter 8 Suggested solutions for Chapter 8 49 Problem 6 What is the relationship between these two molecules? Discuss the structure of the anion that would be formed by the deprotonation of each compound. N 0 N OH H Purpose of the problem To help you recognize that conjugation may be at the back of some related structures. Suggested solution They are tautomers. They differ only in the position of a proton. Each is an acid - the first has an NH roup as part of an amide and the second has an OH group. Deprotonation may at first appear to produce two different anions but they are actually the same because of delocalization of the anion. N 0 N N D N H Problem 7 What species would be formed by treating this compound with: (a) one equivalent; (b) two equivalents of NaNH₂ in liquid ammonia? Purpose of the problem simple problem to help you think about the possibility of selective deprotonation. Suggested solution The more acidic group is the OH about 16) and the less acidic is the alkyne about 35). The alkoxide will be formed first, and then a second deprotonation is possible because the two negative charges are far apart in the dianion and will not significantly destabilize each other. NaNH₂ NaNH₂ 0 Problem 8 The carbon NMR spectra of these compounds could be run in D₂O under the conditions shown. Why were these conditions necessary and what spectrum would you expect to observe? N N H 0 OH spectrum run in DCI/D₂O spectrum run in NaOD/D₂O Purpose of the problem NMR revision and practice at judging the states of compounds at different pHs. Hidden symmetry from conjugation.