Electrophile and nucleophile with example
Electrophile definition and example
The electron-deficient species which tend to attack the substrate at the site of high electron density is called electrophile. The electrophile may be neutral but electron efficient that may have lees then eight electrons in the outer quantum energy level. CCl2, R-N, BF3, AlCl3, CH2 are an example of opposite electrophile species.
It may be positively charged species. eg, NO2+, -R+.
It may be a positive pole of the polar chemical bond. eg, I - Cl(interhalogen), RCOR, RX
Definition and relative order of nucleophilicity
The attacking tendency of a nucleophile to the electron efficient atom is called nucleophilicity.
The nucleophile with a negative charge is always stronger nucleophile than its conjugate acid which is also a nucleophile. eg, OH- > H2O, NH2- > NH3, SH- > H2S, RO- > ROH, RNH- > RNH2
In a set of nucleophiles having the same doner atom the nucleophilicity increases with increasing the electron charge density as that of base properties. eg, OH- > PH-O- > RCO-O-
Nucleophiles whose attacking atoms are within the same row the periodic table, nucleophilicity decreases from left to right as that of electronegativity increases. eg, CH3 > NH2- > OH- > F-
When we go from top to bottom in a group ionization energy decreases also basicity decreases
Neucliphilicty increases in the protic solvent.
It decreases in the aprotic solvent.
Neucleophilicity in the protic solvent, F- > Cl- > Br- >I-, OH- > SH-, NH2- > PH2-, H2O < H2S, NH3 < PH3. The anomaly's behavior can be explained by electric polarization and solvation of nucleophiles in the protic solvent. As we go down in a group in the periodic table atomic volume increase and less solvation take place, hence nucleophilicity increases.
