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An electron-withdrawing group (EWG) is a group or atom that has the ability to draw electron density toward itself and away from other adjacent atoms. [1] This electron density transfer is often achieved by resonance or inductive effects.
Delocalizing the radical ion stabilizes the transition state structure. As a result, the energy of activation decreases, enhancing the rate of the overall reaction. According to the captodative effect, the rate of a reaction is the greatest when both the EDG and EWG are able to delocalize the radical ion in the transition state structure. [7]
An electron donating group (EDG) or electron releasing group (ERG, Z in structural formulas) is an atom or functional group that donates some of its electron density into a conjugated π system via resonance (mesomerism) or inductive effects (or induction)—called +M or +I effects, respectively—thus making the π system more nucleophilic.
In the context of electronic redistribution, an electron-withdrawing group (EWG) draws electrons away from a reaction center. When this center is an electron rich carbanion or an alkoxide anion, the presence of the electron-withdrawing substituent has a stabilizing effect.
For example, in a normal-demand scenario, a diene bearing an electron-donating group (EDG) at C1 has its largest HOMO coefficient at C4, while the dienophile with an electron withdrawing group (EWG) at C1 has the largest LUMO coefficient at C2. Pairing these two coefficients gives the "ortho" product as seen in case 1 in the figure below.
Omega-3 fats are best known for heart health and include:. DHA (docosahexaenoic acid), which supports brain and eye health. EPA (eicosapentaenoic acid), which reduces inflammation and promotes ...
In nature, methoxy groups are found on nucleosides that have been subjected to 2′-O-methylation, for example in variations of the 5′-cap structure known as cap-1 and cap-2. They are also common substituents in O -methylated flavonoids , whose formation is catalyzed by O-methyltransferases that act on phenols , such as catechol- O -methyl ...
Average mortgage rates edge higher for 30-year and 15-year terms as of Wednesday, December 18, 2024, as the Federal Reserve is set to conclude its final policy session of the year.