/sci/ - Science & Math

>>1233060
The R configuration, meaning the hierarchy of the atoms bonded to the chiral carbon atom move in clockwise direction.
The S configuration, in counterclockwise.
Now, how can we see which atoms bonded to the stereogenic carbon atom are of 'higher order' than other atoms? It's simple convention.
As the carbon atom needs to be in a sp3 configuration (or a the bonds look like a tetrahedron), you put the least important atom bonded to the C atom, behind the C atom so you will have the 3 most important ligands to wory about. The least important atom is mostly the H. To see which are increasingly more important, you view the atom number: C<N<O<...
That's the basics.
If you want longer ligands such as a carbonchain, or a carboxyl ligand, it goes a little different. Say, we have a chiral carbon center with 1 H, 1 O, and 2 pentyls, but on one of the pentyls there is an O and on the other, there is a Cl. The pentyl with the Cl> The pentyl with the O, since Cl>O. It's kind of like when you alphabetise a list of names and 2 people start with the same letter, you gotta look for the first difference.
If you have a stereogenic centre bonded to a C, double bonded with, for instance, an O, you have to 'undouble' the double bond, meaning each bond that is extra to an atom, counts as an extra bond to that atom. The picture will make it clear to you (or not).