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(a) In the light of your answer to problem to propose mechanism for the reactions below.

Short Answer

Expert verified

A stable product will be formed via the formation of a non conjugated diene. This non-conjugated diene by loosing from it, will give the product shown above.

Step by step solution

01

Diels-Alder reaction

Diels-Alder reaction was discovered by the German chemists Otto Diels and Kurt-Alder in 1928 for which they got Nobel prize 1950. Diels-Alder reaction is an important organic reaction which includes a substituted alkene in the form of a dienophile and a conjugated diene. It proceeds via concerted mechanism. Diels alder reaction can be used to generate 6 membered rings since there is a simultaneous construction of two new Carbon-carbon bonds.

02

Diene and dienophile

Diene is an organic compound which comprises of two conjugated pi bonds (4 pi bonds) while dienophile is a diene loving compound containing 2 pi electrons. When the interaction between them, occurs a transition state without any additional energy barrier, is obtained.

Here, the diene is

while the dienophile is

03

Mechanism          

First of all, the Diels-Alder reaction of given diene and dienophile generates a product in which double bonds are not conjugated.

Diels-Alder reaction

so a more stable product can be formed by the loss of on heating.

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Most popular questions from this chapter

The following ultraviolet absorption maxima have been measured:

1,3-Butadiene 217 nm

2-Methyl-1,3-butadiene 220 nm

1,3-Pentadiene 223 nm

2,3-Dimethyl-1,3-butadiene 226 nm

2,4-Hexadiene227 nm

2,4-Dimethyl-1,3-pentadiene 232 nm

2,5-Dimethyl-2,4-hexadiene 240 nm

What conclusion can you draw about the effect of alkyl substitution on

UV absorption maxima? Approximately what effect does each added

alkyl group have?

How can you account for the fact that cis-1,3-pentadiene is much less reactive than trans-1,3-pentadiene in Diels-Alder reaction.

An extremely useful diene in the synthesis of many natural products is

known as Danishefsky’s diene. This compound is useful because after

the Diels–Alder reaction it can be converted into a product that could

not be accessed by a typical Diels–Alder reaction. Show the Diels–Alder

adduct and propose a mechanism that accounts for the final products.

Answer the questions below for 1,3,5-cycloheptatriene.

(a)How many patomic orbitals are in the conjugated system?

(b)How many molecular orbitals describe the conjugated system?

(c)How many molecular orbitals are bonding molecular orbitals?

(d)How many molecular orbitals are anti-bonding molecular orbitals?

(e)Which molecular orbitals are filled with electrons?

(f)If this molecule were to absorb a photon of UV light an electron would move between which two molecular orbitals (be specific)?

Norboradiene (Problem 14-55) can be prepared by reaction of chloroethylene with 1,3-cyclopentadiene, followed by treatment of the product with sodium ethoxide. Write the overall scheme and identify the two kinds of reactions.

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