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Organic Chemistry Problem Set 2 for CHEM 231A, Assignments of Organic Chemistry

A problem set for organic chemistry chem 231a students. It includes various tasks such as identifying names and structures of molecules, predicting products of reactions, and explaining the reactivity of lithium diisopropyl amide (lda).

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Pre 2010

Uploaded on 08/18/2009

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Organic Chemistry - CHEM 231A
Problem Set #2
Due Thursday, October 9 at 12:00 pm
40 points total
1. Provide names and/or structures for the following molecules: (10 pts = 2 pts each)
1e. Choose one of the above molecules and draw its enantiomer and at least two non-enantiomeric
diastereomers.
2. Consider lithium diisopropyl amide (LDA): (15 pts)
2a. diisopropyl amine has a pKa of 35. What does this mean? Explain how we
explain this number in terms of the reactivity of LDA. (2 pts)
2b. LDA is considered to be non-nucleophilic. Does this contradict the answer to 2a?
Explain. Why might it not be nucleophilic (consider the relationship between
structure and function of this molecule)? (1 pts)
2c. Consider the reaction of LDA with each of the following molecules. (9 pts = 3 pts each)
For each molecule:
a. Predict the probable product
b. If the molecule acts as an acid, identify the pKa of the acidic part.
c. If the reaction is an acid/base reaction, predict the direction the equilibrium will
lie and provide an overall reaction equilibrium constant.
HO Br
OO
2c1
2c2
2c3
OH
O
O
O
2d. Consider the molecule from question 2c3. If two mole equivalents of LDA are used, a second
reaction results in the formation of a product with the formula C
6
H
7
O
4
Li. What is the structure
of this product? Write a mechanism that accounts for the formation of this product. Why would
2 equivalents be needed for this reaction to occur? Explain. (3 pts)
NLi
+
LD
A
Br
Cl
1a.
I
1c.
1d.
(2R, 3S, 4R) 1-bromo-4-chloro-3-isopropyl-2,4,5-trimethylhexane
H
(2S, 3S, 4S, 5R, 6R) 2-bromo-3-t-butyl-5-ethyl-4-isopropyl-6-trifluoromethyloctane
1b.
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Organic Chemistry - CHEM 231A

Problem Set # Due Thursday, October 9 at 12:00 pm 40 points total

  1. Provide names and/or structures for the following molecules: (10 pts = 2 pts each)

1e. Choose one of the above molecules and draw its enantiomer and at least two non-enantiomeric diastereomers.

  1. Consider lithium diisopropyl amide (LDA): (15 pts) 2a. diisopropyl amine has a pKa of 35. What does this mean? Explain how we explain this number in terms of the reactivity of LDA. (2 pts) 2b. LDA is considered to be non-nucleophilic. Does this contradict the answer to 2a? Explain. Why might it not be nucleophilic (consider the relationship between structure and function of this molecule)? (1 pts) 2c. Consider the reaction of LDA with each of the following molecules. (9 pts = 3 pts each) For each molecule: a. Predict the probable product b. If the molecule acts as an acid, identify the pKa of the acidic part. c. If the reaction is an acid/base reaction, predict the direction the equilibrium will lie and provide an overall reaction equilibrium constant.

HO

Br

O O 2c

2c

2c

OH

O O

O 2d. Consider the molecule from question 2c3. If two mole equivalents of LDA are used, a second reaction results in the formation of a product with the formula C 6 H 7 O 4 Li. What is the structure of this product? Write a mechanism that accounts for the formation of this product. Why would 2 equivalents be needed for this reaction to occur? Explain. (3 pts)

N Li +

LDA

Br

Cl

1a.

I

1c.

1d.

(2R, 3S, 4R) 1-bromo-4-chloro-3-isopropyl-2,4,5-trimethylhexane

H

(2S, 3S, 4S, 5R, 6R) 2-bromo-3-t-butyl-5-ethyl-4-isopropyl-6-trifluoromethyloctane

1b.

  1. Consider the following reactions: (15 pts = 5 pts each) For each reaction:
    1. Identify the nucleophile, electrophile, acid and/or base (more than one may exist).
    2. Predict the possible product(s) for the reaction.
    3. Explain whether the reaction is likely to occur or not.
    4. If the reaction is not likely, explain and suggest how one might change the reactants to facilitate a better reaction.

O

HO

3a

Br 3b NH^2

3c H

O

CH (^3)

H 2 O

F OH

O

OH