Chemistry 251/253

Answer Key

Homework 2

1. The reaction sequence represents one combination of an organolithium reagent and a ketone that may be used to prepare . How many other combinations are possible? 2

2. How many combinations of an organolithium reagent and a carbonyl compound could you use to prepare ? 1

3. is one carbonyl compound that could be used to prepare using organometallic chemistry. Draw the structure of another carbonyl compound that could be used to prepare the same alcohol.O=Cc1ccccc1

4. Draw the structure of A. CC(O)CC=C

5. Draw the structure of B. CC=O

6. Draw the structure of C. CCO

From a retrosynthetic perspective, the analysis looks like this:

Synthetically the preparation of the target molecule looks like this:

7. The general scheme for preparing Grignard reagents may be expressed as . How many of the following compounds are compatible with this scheme? 6 Only HBr would not be suitable.

8. When Al Kane ran the reaction sequence shown below, he obtained the target molecule he desired along with a substantial amount of another compound that gave the attached ¹H-NMR spectrum. Draw the structure of this other compound.

CC(C(=C)C)C(C)(C)O Note that the carbanionic center of the original organolithium reagent is conjugated to the adjacent double bond. This means that there are two nucleophilic centers in the organolithium reagent. The second product arises from nucleophilic addition of the second nucleophilic center to the carbonyl carbon atom of the acetone.

9.O=C1CCCCC1

10.CCC=NC Organometallic reagents add to C=N groups as well as to C=O groups.

11.CC(C)Cl

The oxidation level of the carbon atom in the reactant is -2, while in the product it is -4. The carbon is reduced by the lithium.

13. Draw the structure of the alkene that would produce upon ozonolysis.CCC(=C(C)C)C

14. Ozonolysis of an unknown compound produced a new compound that gave the attached ¹H-NMR spectrum. Draw the structure of the unknown compound.CC1=CCc2ccccc12

15. Draw the structure of the product of the following transformation: CCCC(=O)O

16. How many of the following solvents would be suitable for the preparation of C₆H₅Li? 2 C₆H₆ and CH₃CH₂OCH₂CH₃

C6H6

CCl4

CH3CH2OH

CH3CH2OCH2CH3

17. The general scheme for preparing organolithium reagents may be expressed as . How many of the following compounds are compatible with this scheme? 4 Alkyl fluorides are not used to prepare organometallic reagents.

18. Consider the reaction sequence Draw the structure of compound B.CC(O)CCCCC(C)O

19. The alcohol that is produced by the reaction sequence may be prepared by an alternative synthesis: Draw the structure of compound X.CC(C)(C)C(=O)c1ccccc1

20. Select the conditions that are best suited to achieve the reaction.

21. When Polly Ester attempted to run the reaction shown below, the ¹H-NMR spectrum of the compound she isolated showed clearly that it was not the product she wanted. Draw the structure of the compound that Polly actually isolated.

CC(C)(O)Cc1ccccc1 In this case when the methyl lithium attacks the carbonyl carbon, it displaces an ethoxide ion in a nucelophilic substitution reaction which produces 1-phenylacetone as an intermediate. This intermediate then reacts with additional methyl lithium in a normal fashion. Protonation of the resulting oxyanion yields the observed product.

22. Draw the structure of the aldehyde or ketone that you would use to prepare using an organolithium reagent.C=O

23. Which of the following compounds would not be suitable for the generation of a Grignard reagent that you could use to prepare? D

24. Which of the following compounds would not be suitable for the preparation of using a Grignard reaction? A

25. Draw the structure of the product of the following reaction: CCC(C)C(=O)O

26. Draw the structure of the tetrahedral intermediate formed in the following reaction. Do not include the cation.CCC(C)([O-])C1CCCC1

27. Draw the structure of the product of the following reactions:CC(C)CC(=O)C

28. What is the equilibrium constant for the reaction? 10e-6

29. is an example of a group of compounds known as dipeptides. Draw the structure of the product that would be formed by treatment of this dipeptide with LiAlH₄ followed by adicification with dilute acid.CC(N)CNCCO Refer to Equation 11 and Figure 7 in the Oxidation-Reduction topic for examples that are relevant to this problem.

30. Which of the following methods would not be suitable for the preparation of 1-pentanol, CH₃CH₂CH₂CH₂CH₂OH? Assume an appropriate work-up in all cases.