Define a basic heteroaromatic ring.
In heteroatomatic rings, both pi bonds and nonbonding pairs of electrons are used to satisfy the 4n+2= # of electrons rule. These nonbonding pairs are generally found on an electronegative atom. In the case of a basic heteroaromatic ring, two electronegative atoms are present, one being a nitrogen with a nonbonding pair of electrons. While the other electronegative atom uses its nonbonding pair of electrons to establish aromaticity, the nitrogen remains with its nonbonding pair of electrons free to undergo protonation, thus making the structure basic. Another situation may be that the ring has already established aromaticity without the use of nonbonding pairs of electrons, in which case the nitrogen uses its nonbonding pair of electrons as a means of protonation.