Explain the order of basicity for primary, secondary and tertiary amines.
The order of basicity for primary, secondary and tertiary amines are:
Secondary > Primary > Tertiary > NH3
Amines are basic in nature as they have lone pair of electrons on nitrogen. Therefore, they have a strong tendency to donate this lone pair of electrons to electron acceptors.
The stability of conjugate acids formed is dependent on the extent of H-bonding,and greater the number of H-atoms on N more stable is the conjugate acid.
The conjugate acid of primary amine is the most stable with greater number (3) of H-bonds than > Secondary > tertiary. But primary amines are less basic than secondary as the electron density on the N atom is less and lone pair of electrons are not readily available for protonation.
The two opposing factors i.e. the stability of conjugate acids formed and ease of availability of electrons for Protonation, balance each other in case of secondary amines and it is most basic.