Pi Orbitals

[AdaAda87]

How many Pi molecular orbitals are there in pyridine possess?

A)3
B)4
C)5
D)6
E)7

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[drgreen]

3

 

[jdent]

yep, just count the double bonds. Each double bond is one pi and each triple bond is 2 pi.

 

[wkawk2416]

i thought, two pie orbitals make up one pie bond.

therefore, the answer is 6.

am i wrong?

 

[klutzy1987]

Tricky question depends on how it is worded. Both of you are correct. However i think that i saw that question somewhere and the answer was 6 if i remember correctly.

 

[AdaAda87]

The answer is actually 7. I originally thought it was 6. Does anyone know why it's 7???

 

[klutzy1987]

7?? you sure??
Where is the question from. Tell me not Kaplans.

 

[drgreen]

I stand corrected, it is 6. There are 3 pi bonds, and 6 pi orbitals. 7's a bit of a stretch.

 

[DentalDeac]

Wouldn't there be a lone electron on the nitrogen that could contribute to pi bonding?

Normally the N would have a pair, but since it is + and makes 4 bonds, there would be 1 free electron

 

[AdaAda87]

It was from a PCAT 2003 PCAT test. I still think it's 6, anyone differ?

 

[Lazerous]

I stand corrected, it is 6. There are 3 pi bonds, and 6 pi orbitals. 7's a bit of a stretch.

Wait, how does that work out? Please explain.

 

[niktacal82]

I would say 6; Nitrogen is sp2 ( so 3 sp2 orbitals.) and one P orbital which participates in the pi system of the ring(the double bond with the next carbon in the ring). The lone pair on nitrogen is in one of its 3 sp2 orbitals and not delocalized into the aromatic pi-system. In acidic solution pyridine is protonated and forms this positively charged cation. ( so bond between nitrogen and H+ is co-ordinate bond)...right?

if the answer is 7, then I have no idea