womansraka.blogg.se - Homo lumo diels alder

It is, therefore, concluded that both long-range exchange interactions and dispersion correlations are essentially required in conventional functionals to investigate Diels-Alder reactions quantitatively. Consequently, we found that dispersion correlation correction is also crucial to give accurate barrier height energies. The barrier height energies were also computed for these reactions. As a result, it is found that the long-range correction drastically improves the reaction enthalpies. First, we calculated the Diels-Alder reaction enthalpies that have been poorly given by conventional functionals including B3LYP functional.

cycloadditions (e.g.The possibility of quantitative reaction analysis on the orbital energies of long-range corrected density functional theory (LC-DFT) is presented.

pericyclic reactions have cyclic delocalized transition states and are more stable when the transition stste unvolves (4n+2) electrons (aromatic).

endo product is usually the major product, due to secondary interactions between the pi systems.

stereochemistry of the diene and the alkene is retained.

the combination of electron-deficient diene with electron-rich alkene also works.

Lewis acids also enhance the Diels-Alder reaction by complexing the dienophile.

this allows good electron flow from the diene HOMO to the alkene LUMO.the reaction goes best with alkenes having electron-withdrawing substituents (dienophiles).cyclopentadiene undergoes reaction with itself.cyclic dienes are much more reactive than acyclic dienes.s-cis means the single bond between the two double bonds is cis.the diene must be in an s-cis conformation for this reaction.such transition states are particularly stable when they have (4n+2) electrons.note that the transition state is a 6-membered ring of delocalized pi electrons.overall, two pi bonds are converted to two sigma bonds while making the ring.cycloaddition of a diene to an alkene (usually called a dienophile in this reaction).in most situations, a more stable product means a lower barrier (The Hammond Postulate).Note - this situation of the more stable product having a higher activation barrier is unusual.thermodynamic control requires equilibration to form the more stable product, since it has a higher barrier.thermodynamic control - the more substituted alkene is the more stable product.kinetic control (lower Ea) - the more substituted cation has more + charge, reacts faster.heating the kinetic mixture of products gives the thermodynamic mixture (i.e., mostly 1,4).addition at high temperature favors the 1,4-addition product (thermodynamically controlled).addition at low temperature favors the 1,2-addition product (kinetically controlled).the two ends of the allyl cation may be nonequivalent.conjugated dienes can give 1,2 or 1,4 addition.addition gives a relatively stable allylic cation.conjugated dienes are very reactive towards electrophiles.frontier MOs are the most important for electron pushing.1,3-butadiene - 4 pi MOs (two bonding and two antibonding) with 4 pi electrons.allyl cation (2 pi electrons), allyl radical (3 pi electrons), allyl anion (4 pi electrons).allyl pi system (could be cation, radical, or anion) - 3 pi MOs (bonding, nonbonding, antibonding).ethene - pi bond and pi* antibond, with two electrons in the pi bond.

n atomic orbitals (AOs) combine to make n molecular orbitals (MOs).Molecular Orbitals (MOs) of Conjugated Pi Systems Chem 336 - Spring 1999 - Organic ChemistryIII