Search results
Results from the WOW.Com Content Network
Electron-withdrawing groups exert an "inductive" or "electron-pulling" effect on covalent bonds. The strength of the electron-withdrawing group is inversely proportional to the pKa of the carboxylic acid. [2] The inductive effect is cumulative: trichloroacetic acid is 1000x stronger than chloroacetic acid.
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.
Groups that are electron-withdrawing by resonance decrease the electron density especially at positions 2, 4 and 6, leaving positions 3 and 5 as the ones with comparably higher reactivity, so these types of groups are meta directors (see below).
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 ...
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.
An electron withdrawing group (EWG) will have the opposite effect on the nucleophilicity of the ring. The EWG removes electron density from a π system, making it less reactive in this type of reaction, [ 2 ] [ 3 ] and therefore called deactivating groups .
The substituent R next the amine methylene bridge is an electron-withdrawing group. The original 1928 publication by Thomas S. Stevens [2] concerned the reaction of 1-phenyl-2-(N,N-dimethylamino)ethanone with benzyl bromide to the ammonium salt followed by the rearrangement reaction with sodium hydroxide in water to the rearranged amine.