Concept explainers
(a)
Interpretation: The structural formula for the Diels-Alder adduct formed by cyclopentadiene has to be drawn.
Concept Introduction:
Diels-Alder reaction:
It is the reaction of conjugated dienes with double or triple bonded compounds which are known as “dienophiles”. The reaction is a
Example:
This mechanism shown that three
Diels-Alder reaction to form bicyclic system:
The Diels-Alder adduct formed in the Diels-Alder reaction can also be a bicyclic system which will be obtained when cylopentadiene is used as the diene as shown here:
In this reaction, the cylopentadiene acts as both diene and dienophile and formed a bicyclic system. When it is heated to
(a)
Explanation of Solution
The given reaction is:
The structural formula for the Diels-Alder adduct can be found using the following mechanism of the given Diels-Alder reaction:
In this Diels-Alder reaction, one molecule of cyclopentadienone acts as a Diene whereas the other molecule of cyclopentadienone acts as a Dienophile. The resulted Diels-Alder adduct is a tricyclic product
(b)
Interpretation: The difference in the stability of the given
Concept Introduction:
Stability based on aromaticity:
The term aromaticity means “extreme stability”. So,
The aromatic compounds and anti-aromatic compounds can be distinguished based on Huckel’s
Huckel’s rule of aromaticity is
If
If
(b)
Answer to Problem 20.44P
The difference in the stability of the given ketones has been accounted as:
Cycloheptatrienone is more stable than cyclopentadienone.
Explanation of Solution
The given ketones are:
The stability of these two ketones can be distinguished based on aromaticity as discussed below:
There are two
Huckel’s rule of aromaticity:
Therefore, the given molecule has
There are three
Huckel’s rule of aromaticity:
Therefore, the given molecule satisfies the Huckel’s rule of aromaticity. So, it is an anti-aromatic compound which means it is a highly stable compound.
Hence, the overall discussion makes it clear that cycloheptatrienone is more stable than cyclopentadienone.
Want to see more full solutions like this?
Chapter 20 Solutions
Organic Chemistry
- (A) Which triene has the smallest heat of hydrogenation? Explain why. (B) Which triene can be reactive in the Diels-Alder reaction? (C) Which triene is the most reactive in the Diels-Alder reaction?arrow_forwardCyclopropenones are described as having aromatic character. How would you account for this, given that the ring contains three ℼ-electronarrow_forwardCompounds A and B are isomers having the molecular formula C4H8O3. Identify A and B on the basis of their 1H NMR spectra.Compound A: δ 1.3 (3H, triplet); 3.6 (2H, quartet); 4.1 (2H, singlet); 11.1 (1H, broad singlet)Compound B: δ 2.6 (2H, triplet); 3.4 (3H, singlet); 3.7 (2H triplet); 11.3 (1H, broad singlet)arrow_forward
- 2) A Diels-Alder reaction yields the following compound. Please write the structure of diene and dienophile, and synthesize the dienophile from a starting material with no more than four carbon. "CO₂Etarrow_forward(a) Complete the following sequence of reactions (i.e., give the structure for compounds A and B), giving structural details of all key intermediates. heat & A COOCH3 H₁₂ Ni (b) Provide the bond line structures for the pair of compounds used for the Diels-Alder synthesis of the compound shown below. O B COOCH3 (c) Draw the two major products obtained when (3E,5Z)-2,2,3,6,7-pentamethylocta-3,5-diene reacts with HBr at low and high temperatures. Label the products as the kinetic or thermodynamic product AND, if applicable, use dashes and wedges to show the correct stereochemistry in the obtained products.arrow_forwardOf the three 1,4-diphenyl-1,3-butadiene isomers (E,E or E,Z or Z,Z) indicate the most suitable diene that can be used as a reactant in a Diels-Alder reaction. Explain your choice.arrow_forward
- Methotrexate, a drug that inhibits the metabolism of folic acid, is used in the treatment of a variety of cancers and autoimmune disorders such as rheumatoid arthritis. (a) GIve the hybridization of each N atom in methotrexate. (b) In what type of orbital does the lone pair of each N reside? (c) Explain why the bicyclic ring system that contains four N atoms is aromatic.arrow_forwardWhich of the following compounds are aromatic and anti-aromatic? Give justifications for your answer. i) ii) iii) +, iv)arrow_forwardTo be aromatic, a molecule must have 4n + 2 πs electrons and must have a planar, monocyclic system of conjugation. Cyclodecapentaene fulfills one of these criteria but not the other and has resisted all attempts at synthesis. Explain.arrow_forward
- Illustrate the resonance effect of the methoxy group -OCH3, on the structure of the benzene ring. Draw all the oissuvke resonance forms of methoxybenzene, including the hybrid Based on the structures, explain how the presence of the -OCH3 group affects: (i) the reactivity of the benzene ring towards electrophilic attack (ii) the orientation or point of attack of an incoming electrophilic reagent on the benzene ring.arrow_forwardCompound X (molecular formula C10H12O) was treated with NH2NH2, −OH to yield compound Y (molecular formula C10H14). Based on the 1HNMR spectra of X and Y given below, what are the structures of X and Y?arrow_forward2. Hexamethylbenzene undergoes free-radical chlorination to give one monochlorinated product (C₁2H17C1) and four dichlorinated products (C12H16C12). These products are easily separated by GC-MS, but the dechlorinated products are difficult to distinguish by their mass spectra. Draw the monochlorinated product and the four dichlorinated products, and explain how ¹3C NMR would easily distinguish among these compounds. (6 pts) Cl₂/hv Ch/v monochlorinated product dichlorinated products CIarrow_forward
- Organic ChemistryChemistryISBN:9781305580350Author:William H. Brown, Brent L. Iverson, Eric Anslyn, Christopher S. FootePublisher:Cengage Learning