1. OCHM – Organic Synthesis
Question Information
Q-Bank
MCAT
Sim
Non-Sim
Subject
Organic Chemistry
Foundation
OCHM – Organic Synthesis
Validity
5 years
Author(s)
Reyes, V. M.
Reviewer(s)
Editor(s)
Passage Information
Passage ID
Media ID(s)
Passage Stem
Synthetic organic chemistry is arguably the most important and most active branch of
organic chemistry, and a casual inspection of the chemical literature will attest to that.
Synthetic organic chemists are especially in high demand in the drug discovery and manufacturing as well as the big bio-pharma industries. Organic reactions named after their discoverers (“named organic reactions”) alone number a few hundred, and most of them are intended for the synthetic route to novel organic compounds.
Synthetic organic reactions involve the formation of new covalent bonds usually involving C-atoms and the reassembly of old ones. The product is usually an organic molecule larger than the reactants involved, and ready for the next synthetic reaction.
The ultimate aim is the creation of a new drug or material for specialized purposes (e.g., biomaterials, etc.). In this module, shall focus on the Diels-Alder reaction, an important and time-tested way to create cyclic organic compounds.

2. The Diels-Alder reaction is a reaction between a conjugated diene (a.k.a., 1,3-diene) and an alkene (a.k.a. olefin ), or sometimes an alkyne (a.k.a. acetylene), to form a 6-membered cyclic adduct containing one or two double bonds in the case of olefins and acetylenes, respectively: R R P T P T
heat +
pressure Q U Q U S S
dienophile
(alkene or alkyne)
conjugated diene
cyclic adduct
In the reaction above, P, Q, R, S, T and U are suitable alkyl groups. The alkene or alkyne reactant (red bond in the dienophile in case of alkynes) is often termed the “dienophile” (phile = “loving”; dienophile = “diene-loving”) because of its tendency to react with the conjugated diene. The reaction is carried out under heat and pressure. Since the Diels-Alder reaction produces a cyclic adduct, it is considered as a cyclo-addition reaction of the [4+2] type since it involves 4π electrons of the 1,3-diene and 2π electrons of the olefin (or acetylene).
For example, applying heat and pressure to a mixture of 1,3-butadiene and acrolein yields 1,2,5,6-tetrahydrobenzaldehyde: +
10 kbar ∆
1,3-butadiene
acrolein
1,2,5,6-tetrahydrobenzaldehyde
1,3-butadiene plays the role of the conjugated diene, and acrolein the dienophile; the resulting cyclic adduct is 1,2,5,6-tetrahydrobenzaldehyde. Reactivity between diene and dienophile depends on the substituents either molecule has, with electron-donating on the former and electron-withdrawing groups on the latter enhancing adduct formation.

3. Question Attributes #1 (QID: 000000)
Passage References
PMID/Page #
Title of Publication or Book
Type
R. Brewster & W. McEwen, Organic Chemistry textbook
R. W. Griffin, Jr., Modern Organic Chemistry textbook
(N/A)
en.wikipedia.com, youtube.com internet
(N/A)
Author’s own lecture notes
Question Attributes #1 (QID: )
Topic Blueprint
The Diels-Alder Reaction
Competency
MCAT: BS-2: Application of Concepts & Principles
Objective
To gain an understand of the Diels-Alder reaction and be able
to predict the product of the reaction given the reactants.
Media ID(s)
Question ID
Question Stem #1
Cyclopentadiene is known to undergo Diels-Alder adduct formation near room temperature. Predict the molecular structure of the resulting product. 2 ?
cyclopentadiene

4. I. II. IV. III. Answer Choices #1 A) I B) II C) III D) IV Correct: D)
III dicyclopentadiene
IV.
III.
(Cont’d. on the next page.)

5. The correct answer is C, molecule III.
Explanation #1
The correct answer is C, molecule III.
The first step is to identify the diene and the dienophile. Since in this case they are identical molecules, it is important to identify the conjugated C=C bonds in the diene
and the electrophilic C=C or CΞC in the dienophile. They are identified on the right hand side of the above reaction forming incipient bonds. It is thus easy to see that this intermediate will give rise to molecule III.
(Choice A) This molecule is cycloheptatriene and is an incorrect choice. It is composed of eight carbon atoms in cyclic, conjugated form. Its formation would have involved the recyclization/reassembly of two molecules of linearized cyclopentadiene which is expected to have 10 carbon atoms, five from each linearized cyclopentadiene, thus this molecule fails to account for two carbon atoms.
(Choice B) This choice in incorrect. This molecule is the Diels-Alder adduct product
between anthracene and singlet oxygen. This choice may also be eliminated by the
fact that the two oxygen atoms in it are unaccounted for.
(Choice D) This choice is also incorrect. This compound is azulene, the blue
chromophore in chamomile and the blue mushroom. It has 10 π electrons and hence
aromatic by Huckel’s rule. The synthetic route to azulene does not involve the Diels-
Alder reaction.
(Cont’d. on the next page.)

6. Educational objective: To gain an understand of the Diels-Alder reaction and be able to predict the product of the reaction given the reactants.
References #1
PMID/Book
Title of Publication or Book
Verifications #1
Yes / No
The question is at the Application or higher cognitive level.
Yes / No
The question is based on a realistic clinical scenario.
Yes / No
The question has at least one close distracter, and other options have
educational value.
Yes / No
The question is appropriate to the entry level of nursing practice.
Yes / No
The explanation is short and concise, yet thorough.
Yes / No
The question has an appropriate table/flow chart/illustration.