Question

Which orbitals contain the lone pairs on the nitrogen atoms labeled i and iſ in the imidazole ring? a. i= p; ii = sp3 b. 1= p; ii = spa OC. 1 = sp?; ji = sp d. 1 = sp2: = sp3

Answer 1

correct option is (b). i = p, ii = sp2

for i,

N of NH is sp2 hybridized and its lone pair of electron takes part in conjugation. An sp2 hybridized N atom has 3 sp2 orbitals and 1 p orbital. The sp2 orbitals are coplanar and p orbital is perpendicular to sp2 orbital plane.

Here, this N has,

2 NC bond due to overlapping of sp2 hybridized orbitals.

1 NH bond in sp2 hybridized orbital.

Thus sp2 orbitals are filled and p orbital is empty.

Rest of lone pair of electron of N will come in p orbital.

for (ii),

This N is sp2 hybridized and its lone pair of electrons are not involved in aromaticity.

As sp2 hybridized N has 3 sp2 orbitals, and 1 p orbital.

First sp2 orbitals will filled.

Thus N form 2NC bond which are in sp2 orbitals.

Thus one sp2 orbital is empty, thus lone pair of electron will occupy this sp2 hybridized orbital.