Why is maleic anhydride a good dienophile

Cyclic dienes work well in this reaction. For example, a reaction between 1,3-cyclohexadiene and vinyl chloride yields a bicyclic reaction product. Interestingly, many Diels-Alder reactions occur much faster in water than in organic solvents. Scientists are still working on finding out why aqueous environment accelerates this reaction. The details of the mechanism of Diels-Alder reaction reaction are somewhat debated but experimental and computational arguments suggest that the reaction with typical electron-rich dienes, and electron-poor dienophiles proceeds via asynchronous concerted mechanism.

You can think of the electron-rich diene as a nucleophile with partially delocalized electrons. For the bond formation to take place, these electrons shall "flow" into a Lowest Unoccupied Molecular Orbital LUMO in the dienophile, which at this stage acts as an electrophile. But the "flow" or charge transfer of electrons from diene to dienophile makes the dienophile more nucleophilic, and the diene, which has lost electrons, becomes at the same time more electrophilic.

Thus, the electrons from HOMO of the dienophile can now "flow" to LUMO of diene; for the formation of the second bond the dienophile acts as a nucleophile.

In the case of symmetric dienophiles, such as ethene or maleic anhydride, each end of the double bond can act with equal probability as the electrophilic site in the initial charge transfer from HOMO to LUMO. Furthermore, once the diene and the dienophile are properly positioned to allow for the charge transfer between the diene and the dienophile, the formation of two new sigma bonds occurs so rapidly that there are no zwitterionic or bi-radical intermediates.

Thus, the Diels-Alder reaction is a concerted reaction. The orbital interactions in the Diels-Alder reaction can be also visualized as a diagram of orbital energies. Photo-electron ionization experiments reveal that ionization energies of 1,3-butadiene and ethene are 9.

Electron transmission spectroscopy reveal that electron affinities of 1,3-butadiene and ethene are It's very significant! Why is maleic anhydride a good dienophile?

Truong-Son N. Dec 7, Maleic anhydride looks like this: It has substantial pi electron density contribution from the nearby carbonyl carbons, which tends to increase the kinetic favorability in a Diels-Alder reaction, sometimes even with a seemingly sterically-hindered mechanism.

The orbital overlap during the reaction looks more like this: Normally one would expect the exo product because it has less steric interference, but because the "secondary" orbital overlap with the extra pi electron density from the carbonyl carbons makes the endo product the kinetically favorable product, even though the exo product is thermodynamically favorable , we get the endo product first.

Related questions Question a. Example C has an alkyne as a dienophile colored red , so the adduct retains a double bond at that location.

This double bond could still serve as a dienophile, but in the present case the diene is sufficiently hindered to retard a second cycloaddition. The quinone dienophile in reaction F has two dienophilic double bonds. However, the double bond with two methyl substituents is less reactive than the unsubstituted dienophile due in part to the electron donating properties of the methyl groups and in part to steric hindrance. In all cases the configuration of the reactant is preserved in the adduct.

Of the following dienes, which are S-trans and which are s-cis? Of those that are s-trans, are they able to rotate to become s-cis? Steven Farmer Sonoma State University. Objectives After completing this section, you should be able to determine whether or not a given compound would behave as a reactive dienophile in a Diels-Alder reaction. Key Terms Make certain that you can define, and use in context, the key terms below.

Study Notes Make sure that you understand that the s -cis and s -trans forms of a diene such as 1,3-butadiene are conformers, not isomers. Stereochemistry of the Diels-Alder reaction We noted earlier that addition reactions of alkenes often exhibited stereoselectivity, in that the reagent elements in some cases added syn and in other cases anti to the the plane of the double bond.

The essential characteristics of the Diels-Alder cycloaddition reaction may be summarized as follows: The reaction always creates a new six-membered ring. When intramolecular, another ring may also be formed. The diene component must be able to assume a s-cis conformation. Electron withdrawing groups on the dienophile facilitate reaction. Electron donating groups on the diene facilitate reaction. Steric hindrance at the bonding sites may inhibit or prevent reaction.

The reaction is stereospecific with respect to substituent configuration in both the dienophile and the diene. Exercises Questions Q Solutions S