organic substitution problem/hybrid orbitals

[BoneMental]

Howdy everyone,

I'm having an issue with a few concept in my organic notes.

1) During an Sn2 reaction, I understand that the transition state has 5 bonds. However, I am told the carbon is sp2 hybridized. I don't understand how this works....? I am also confused how the transition state is trigonal bipyramidal...

2) If you form hybridized sp2 orbitals in a carbon, wouldn't they have an n = 2? My book says its n = 3, and I feel this is incorrect. Why would hybridized orbitals jump a whole quantum number?

I appreciate the help everyone! Here's a clover for good luck.

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[DougTPR]

1) During an Sn2 reaction, I understand that the transition state has 5 bonds. However, I am told the carbon is sp2 hybridized. I don't understand how this works....? I am also confused how the transition state is trigonal bipyramidal...

An sp2 hybrid has an unhybridized p orbital that is perpendicular to the plan of the trigonal sp2 orbitals. the additional 2 "bonds" in the transition state (although bond is stretching it a bit) are the top and the bottom of the trigonal bipyramid.

2) If you form hybridized sp2 orbitals in a carbon, wouldn't they have an n = 2? My book says its n = 3, and I feel this is incorrect. Why would hybridized orbitals jump a whole quantum number?

Now, I don't know why you would have a need for quantum numbers for orbitals, but since an sp2 orbital on a C atom is made from 2s and 2p orbitals (n = 2) then the hybrids would also be in the 2nd energy shell (n = 2).