Inductive and mesomeric effects

-ve ion, electron rich species, attracted to positively charged atoms

+ve ion, electron deficient species, attracted to negatively charged atoms

• withdrawal or donation of electron density along a sigma bond. • The effect diminishes rapidly as chain length increases

• the electrons are attracted towards the most electronegative atom. • the polarization of the electron density of a sigma bond caused by the electronegativity of a nearby atom

• electron donating inductive effect (EDG) - when atttached to carbon, less electronegative, electrons attracted to carbon

• electron withdrawing inductive effect (EWG) - when attached to carbon, more electronegative, electrons is pulled from carbon

ie.Br, Cl, OH, NO2, NH2, CN, CHO, COOH

ie Alkyl groups, CH3… Mg, Li

• also known as resonance • withdrawal or donation of electron density, operates via pi and lone pair electrons • Effect does not decrease with increasing distance (in conjugated systems)

-the re-distribution of electrons which takes place in unsaturated molecules and especially in conjugated systems via their pi bonds.

+ M groups generally contain a lone pairs of electrons or a pi bond ie Cl, OH, alkenes

electron withdrawing mesomeric effect (EWG) -pi system accepts electrons

• electron donating mesomeric effect (EDG) - pi system donates electrons or lone pair is donated

2

4

• M groups generally contain an electronegative atom and a pi bond ie NO2, COOH, CHO

• electron donating group • orto, para • 2,4

• electron withdrawing group, • meta • 3 • except halogens (-X) which are deactivating BUT direct ortho / para

3

ethanoic acid CH3COOH