Electron withdrawing groups (EWGs) are atoms or functional groups that have a high electronegativity, which causes them to attract electrons towards themselves in a chemical bond. This results in a partial positive charge on the atom they are attached to.
Electron withdrawing groups decrease the electron density around the atom they are attached to, making it more difficult for that atom to participate in reactions. This can make the molecule less reactive overall, as the atom is less likely to form bonds with other atoms.
Some common electron withdrawing groups include halogens (such as fluorine, chlorine, and bromine), carbonyl groups (such as ketones and aldehydes), nitro groups, and cyano groups. These groups are often used in organic synthesis to control the reactivity and properties of molecules.
Electron withdrawing groups can increase the acidity of a molecule by stabilizing the conjugate base. This is because the withdrawal of electrons towards the EWG makes it easier for the conjugate base to accept a proton. This effect is commonly seen in carboxylic acids, where the presence of electron withdrawing groups on the adjacent carbon atoms can greatly increase the acidity of the carboxylic acid group.
Yes, electron withdrawing groups can affect the physical properties of a molecule. For example, the presence of EWGs can increase the melting and boiling points of a compound, as well as its polarity and solubility in polar solvents. This is because the EWGs have a stronger attraction for other molecules, making it more difficult for them to separate and for the compound to change states.