CHEM 2312



Answer Key

July 2, 1998

Dr. Hanson

1. For the following compounds, provide a name where a structure is given or provide a structure where a name is given. IUPAC names are always acceptable, common trivial names are also acceptable. (12 points)


Answer: 5,5-dimethylhexanal


Answer: 3-chloro-2-pentanone

c) 3-methanoylcyclobutanone

Answer: a four membered ring with a ketone functionality at C1. AT C3 (the corner opposite the carbonyl), an aldehyde (a methanoyl group) is the substituent.

d) 2-propanoylnitrobenzene

Answer: A ketone with an ethyl group on one side of the carbonyl and a 2-nitrophenyl group on the other.

2. Propose a synthetic route to each of the following compounds, beginning with benzene and using any other organic or inorganic reagents as required. (15 points)


Answer: Freiedel-Crafts acylation of benzene gives propanoylbenzene. The acyl group is a meta director, so nitration gives the 3-propanoyl nitrobenzene. Reduction of the nitro group gives the 3-propanoyl aniline. Diazotization with sodium nitrite in sulfuric acid gives the diazonium bisulfate. Sandmeyer reaction with cuprous oxide (Cu2O) with cuprate ion (Cu2+) in water gives the 3-propanoyl phenol. Alkylation of the phenol with iodoethane gives 3-propanoyl ethoxybenzene as shown. (Note: technically, one may need to protect the alkanoyl group during the reduction of the nitro compound. This can be done using a cyclic ketal which is removed under acidic hydrolysis.)


Answer: This phenol is most easily made by nucleophilic substitution. Chlorination of benzene with Cl2 and FeCl3 (or bromination with Br2 and FeBr3) gives chlorobenzene (or bromobenzene). The chloro group is an ortho-para director and so after two nitrations the product is 2,4-dinitrochlorobenzene. Nucleophilic substitution of the chloride with hydroxide gives the 2,4-dinitrophenol as shown.

3. For the following compounds, order them by increasing acidity (i.e., least acidic on the left and most acidic on the right). (10 points)

Answer: E<A<B<D<C

4. Provide a detailed, step-by-step mechanism for the following transformation. Show all steps explicitly, including all protonation and deprotoanation steps. (18 points)

Answer: The first step of the mechanism is the protonation of the carbonyl. In the second step, the resulting carbocation reacts with the nucleophilic nitrogen of hydroxylamine. In the third step, the product of the nucleophilic attack is deprotonated on nitrogen. In the fourth step, the hydroxyl group of the resulting product is protonated to make a good leaving group, water. In the fifth step, the water departs to generate a new carbocation (with an NHOH substituent). In the sixth and final step, this carbocation is deprotonated to generate the product oxime.

5. Complete the following reaction sequences, providing starting materials, products, or reagents as required. (30 points)


Answer: a Wittig reaction. The products are the alkene (2-methyl-1-butene) and triphenylphosphine oxide.


Answer: An aldol condensation. The product is the 2-methyl-3-hydroxypentanal or (if dehydration is spontaneous) the 2-methyl-2-pentenal).


Answer: phenol


Answer: Cyanohydrin formation. The product is benzaldehyde cyanohydrin.


Answer: Acetal formation. The products are ethanal diethyl acetal and water.


Answer: The first two reagents add across the carbonyl to give 4-methyl-2-pentanol. The third reagent is an oxidant that takes this secondary alcohol to 4-methyl-2-pentanone.

6. Answer the following questions about the aldol reaction. (15 points)

a) Mixed aldol reactions generally are not synthetically useful. Why?

b) Which of the following would be exceptions to this rule, i.e. aldehydes that can be used as one component in a mixed aldol reaction: butanal, methanal, benzaldehyde, and 1-methanoylcyclohexane?

c) 3-Methyl-2-cyclopentenone can be prepared by a reaction related to the aldol reaction from an acyclic dione. What is this dione?


a) They generate a mixture of products, if both aldehydes can act as both enolate nucleophile and carbonyl substrate.

b) The exceptions are the aldehydes with no alpha hydrogens: methanal and benzaldehyde.

c) (Note that the name has been corrected in the key: 3-methyl-2-cyclopentenone). The precursor is 2,5-hexanedione.