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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.
The +M effect, also known as the positive mesomeric effect, occurs when the substituent is an electron donating group. The group must have one of two things: a lone pair of electrons, or a negative charge. In the +M effect, the pi electrons are transferred from the group towards the conjugate system, increasing the density of the system.
The captodative effect is the stabilization of radicals by a synergistic effect of an electron-withdrawing substituent and an electron-donating substituent. [2] [3] The name originates as the electron-withdrawing group (EWG) is sometimes called the "captor" group, whilst the electron-donating group (EDG) is the "dative" substituent. [3]
A bicycloheptane acid with an electron-withdrawing substituent, X, at the 4-position experiences a field effect on the acidic proton from the C-X bond dipole. [4] A bicyclooctance acid with an electron-witituent, X, at the 4-position experiences the same field effect on the acidic proton from the C-X bondole as the related bicylcoheptane.
Electron withdrawing groups (which can stabilize the molecule by increasing charge distribution) or electron donating groups (which destabilize by decreasing charge distribution) present on a molecule also determine its pK a. The solvent used can also assist in the stabilization of the negative charge on a conjugated base.
If the electronegative atom (missing an electron, thus having a positive charge) is then joined to a chain of atoms, typically carbon, the positive charge is relayed to the other atoms in the chain. This is the electron-withdrawing inductive effect, also known as the -I effect. In short, alkyl groups tend to donate electrons, leading to the +I ...
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.
Ketones and aldehydes with electron-withdrawing substituents react more readily with diazoalkanes than those bearing electron-donating substituents (Table 2). In addition to accelerating the reaction, electron-withdrawing substituents typically increase the amount of epoxide produced (Table 2).