AL chem: bacisity(考試)

1.
look at how many sigma bond and lone pair are there. sigma bond & lone pair come from hybridized orbitals, while pi bond comes from unhybridized orbitals.
at that Nitrogen, there're 2 sigma bonds and a lone pair, requiring three hybridized orbitals. (due to conservation of no. of orbitals,) s- and two p- orbitals are hybridized, thus sp2 .


2.
note that all 4 nitrogen are basic, and are incorporated in the aromatic system.
you should remember that the aromatic system helps to lower the energy of the molecule, thus stabilizing it. any changes that disrupt the aromaticity would destabilize the molecule, thus reaction is not feasible.

look at delta-N. notice that the lone pair is in p-orbital, which is NOT involved in the pi-bond formation. when the lone pair is donated to H(+), pi-bond is still conserved, and aromaticity is not disrupted.

and the other three nitrogen.. the lone pair is involved in pi-bond formation. donation of it would destroy the conjugation (s pi-bond can no longer be formed), thus aromaticity is not conserved. reaction (protonation) is less feasible.

(II) N- delta has 5 outermost electrons, 2 of them are used for lone-pair formation, 1 of them is used to form single bond with adjacent C atom, the remaining are used for double bond forming with C atom. So,

lone pair = 1 pair electron cloud
single bond with C atom = 1 pair electron cloud
double bond with C atom = 1 pair electron cloud

- Sp2 = 3 pairs electron clouds

The bascity of the compound is dertermined by the ability to accept H ions or the relative stability between the products than its reactants.

Sp2 give planar structure (120 degree), easier to accept the hydrogen ion as the reaction can be occured easily at the same plane.

SP3 give 109.5 degree, more difficult to accept H+ ions at the same plane or due to steric hindrance made by CH3 (methyl group). Reaction is less feasible.