Chapter 19: Enolate Anions
Problem 19.80 The following molecule undergoes an intramolecular reaction in the presence of pyrrolidium acetate, the protonated
form of pyrrolidine. Draw the product of this reaction, assuming that a dehydration reaction takes place.
Intramolecular reactions are favored that produce five or six-membered rings, as in this example.
Problem 19.81 Organocuprates predominantly react to give lA-addition products with
carbonyl species, while
Grignard reagents often add to the carbonyl, in a process referred to as 1,2-addition. To increase the yield of 1,4-addition products
CuI is added to convert an easily prepared Grignard reagent into a organocuprate reagent
(during the reaction). Predict the
major product and stereochemistry of the following reaction, assurJ1ing the more stable chair product predominates.
CuI, THF, -30°C
2. Equilibration to
more stable chair
The predominant product chair conformation has both the methyl group a.,nd the alkyl group equatorial.
Chapter 20: Conjugated Systems
SolutWns to the Problems
Problem 20.1 Which of these terPenes (Section 5.4) contains conjugated double bonds?
An aggre gati ng
Only the a.ggregating pheromone of bark beetles (c) has conjugated double bonds.
Problem 20.2 Estimate the stabilization gained due to conjugation when I,4-pentadiene is converted to
Note that the answer is not as simple as comparing the heats of hydrogenation of 1,4-pentadiene and
Although the double bonds are moved from unconjugated to conjugated, the degree of substitution of one of the double .
bonds is also changed; in this case from a monosubstituted double bond to a
disubstituted double bond.'To answer
.this question, you must separate the effect that is the result of conjugation from that caused by a change in the degree of
As stated in the question, there are actually two important
to be addressed.
is best to isolate the two
different interactions by considering
systems in Table 20.1. First, trans-l,3-pentadiene has an
internal double bond while 1,4-pentadiene does not. Internal double bonds are lower in energy because they are
more highly substituted. A good estimate of the stabilization energy provided by having an internal yersus
terminal double bond is 12 kJ/mol, calculated as the difference in energy between I-butene
The overall difference in energy between 1,4-pentadiene