Question

The lone pairs on pyrimidine are not delocalized because of which factor?

a. The lone pairs are in sp3 orbitals.
b. The lone pairs are in sp orbitals.
c. The lone pairs are in orbitals at 90 degrees to the pi system.
d. None of the above.

Answer 1

The lone pairs on pyrimidine are not delocalized because they are contained in sp³ orbitals which are at 90 degrees to the π system and cannot overlap to participate in resonance.

Step-by-step explanation:

The lone pairs on pyrimidine are not delocalized because of which factor? The answer is c. The lone pairs are in orbitals at 90 degrees to the π system. Lone pairs that are in sp³ hybrid orbitals are not in the same plane as the π system and thus cannot participate in delocalization. For resonance to occur, the lone pair needs to be in an unhybridized p orbital or an sp² orbital that is parallel to and can overlap with the π system. Since sp³ hybrid orbitals are tetrahedrally arranged around the atom, the lone pairs contained within them will not be able to interact with the π system, thereby preventing delocalization.

Answer 2

The question is incorrect. It should read:

The lone pairs on pyrimidine are delocalized because of which factor?

a. The lone pairs are in sp3 orbitals.

b. The lone pairs are in sp orbitals.

c. The lone pairs are in orbitals at 90 degrees to the pi system.

d. None of the above.

Answer:

d. None of the above.

Step-by-step explanation:

The nitrogen in pyrimidine is not sp³ hybridized. That means that this pair of electrons is not localized to this nitrogen and is free to move, which is actually what gives rise to pyramidine's resonant structures.