help! confused.. pi bonds

[sjung1]

I'm a bit confused..
so are pi bonds the actual bond that's between the orbitals (the black line)
or is it the blue and pink?

I read on this forum that the alkyne pi bonds were perpendicular which means that pi bonds are the pink and blue
but in the barons DAT prep book, one of the questions says that in ethene, the pi bond and the sp2 hybridized carbons are parallel..

which is correct?

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[mehc012]

I'm a bit confused..
so are pi bonds the actual bond that's between the orbitals (the black line)
or is it the blue and pink?

I read on this forum that the alkyne pi bonds were perpendicular which means that pi bonds are the pink and blue
but in the barons DAT prep book, one of the questions says that in ethene, the pi bond and the sp2 hybridized carbons are parallel..

which is correct?

The blue and the pink are p-orbitals. Pi bonds form when the p-orbitals on adjacent atoms are parallel; the electrons delocalize into a bonding orbital in the space between the parallel atomic p-orbitals (represented by the black lines). If an atom participates in multiple pi bonds, those bonds (which are oriented in either the x, the y, or the z planes) will be oriented perpendicularly to each other because the p-orbitals which form them were oriented perpendicularly to each other.

Pi bonds are weaker than sigma bonds because there is no direct orbital overlap. Instead, they are only the interaction of parallel, non-overlapping atomic orbitals.

Interestingly, while sigma bonds can be formed by s orbitals, hybridized orbitals (sp, sp2, sp3, etc) or p orbitals, pi bonds require an orbital to exist 90 degrees from the one participating in a sigma bond...which limits pi bonds to p orbitals in all cases you will encounter, as you don't have to worry about transition metals and whatnot.

 

[mehc012]

I'm a bit confused..
so are pi bonds the actual bond that's between the orbitals (the black line)
or is it the blue and pink?

I read on this forum that the alkyne pi bonds were perpendicular which means that pi bonds are the pink and blue
but in the barons DAT prep book, one of the questions says that in ethene, the pi bond and the sp2 hybridized carbons are parallel..

which is correct?

The carbon can't be parallel to anything...it's just an atom. The sigma bond formed by the overlapping sp2 hybridized orbitals, however, can be thought of as a line.

Pi bonds, on the other hand, are most easily considered as oriented in a plane, rather than a line. The plane will always be contain the sigma bond, and will also be parallel to the p-orbitals which form it. Those p-orbitals are perpendicular to the sigma bond line (pink orbital in your picture is perpendicular to the sigma bond), as well as to other p-orbitals on the same atom.

Therefore, if there are 2 pi bonds on the same atom, whether through an alkyne or 2 double bonds, those two will both intersect the sigma bond, but will be perpendicular to each other. Picture a plane passing through ALL of the pink parts and another plane passing through ALL of the blue parts: those two planes are perpendicular to each other, even though they're all bonding the same 2 atoms and one dimension parallels (and contains) the sigma bond.