An electron withdrawal group (shortly: electron vacuum) is a substituent, usually organic, in such a way that the electron cloud around a reaction center (the atom, usually carbon, to which this substituent is bound) is deformed such that its electrons are pulled out. This results in a partially positively charged reaction center and a partially negatively charged substituent. Electron-withdrawing groups always have a relatively large electronegativity value or are internally highly polarized. Examples
Examples of electron-withdrawing groups are:
Alkyl groups, which are normally electrically propellant, can be converted into electron withdrawing groups by, for example, placing fluorine atoms or nitro groups. For example, a methyl group is strongly electron-propellant, while a trifluoromethyl group is strongly electron-emitting.
A phenyl group has a double character: it can exist as an electron piston or as an electron spindle, depending on the situation. Reactivity
The presence of an electron-withdrawing group thus causes an electron shift and a corresponding charge shift. This makes the reaction center and the neighboring atoms extra reactive. Electron-withdrawing groups can stabilize certain negatively charged reactive intermediates (such as carban ions) because they spread the negative charge. Also see
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