I seem to remember that carbon can have an sp2 hybrid orbital. If that’s the case, none of the electrons have been promoted, right?
Oh, looking in this book I have, it seems that some are, but I don’t get it yet. Is this the kind of thing that would happen to form a double bond between carbons?
Is there someone here who actually enjoys answering this stuff enough that I could just use email sometimes and not clutter the board?
cough Well, I didn’t pay religious attention in organic chemistry, buuuut… my notes say that to determine what hybridization a molecule has, look at the number of groups that are attached to the central atoms, NOT the kind of bonds… reading from a handout I happened to save…
SP2 hybridized carbon atom: each SP2 orbital can form a sigma bond, therefore, a total of 3 sigma bonds can be formd per carbon atom
Each p orbital can form a pi bond, therefore, a total of 1 pi bonds can be formed per carbon atom.
Shorthand: An SP2 hybridized carbon will form one double bond and two single bonds. Look up “ethylene” at chemfinder.camsoft.com
Eeek. I don’t know if that was any help at all. Maybe I don’t enjoy answering chemistry questions…
Just a bit of info: a saturated carbon centre (ie no double bonds) has four degenerate sp3 orbitals. Similarly, the 3 sp2 orbitals in, say, ethylene are similarly degenerate. As almost invariably these orbitals are completely filled (the exception being ions, radicals and carbenes), so promotion is not really an issue under normal conditions (exceptions being high temps, light, etc).
Feel free to mail me, although if you have a few questions like this, try askme.com, there’s a good org chem section with some pretty damn smart chemists there. And one or too borderline idiots;)