00:01
All right, we've got a couple of molecules here, or maybe it's only one molecule.
00:05
We don't know yet.
00:06
But we need to assign the stereochemical designation to each carbon in this structure for these two potential different molecules, and then decide if they are the same molecule, a different molecule altogether, or maybe just just a stereoisomer.
00:38
Let me finish drawing these up.
00:43
And then we have a hydrogen up here.
00:47
Wedged bromine dash to oh h.
00:53
Wedged bromine and a dash to a hydrogen.
00:59
Okay, i'm going to start on the left.
01:01
And what i always like to do is if i do not have the lowest priority substituent in the back, in this case the lowest priority substituents is hydrogen and it's not in the back.
01:18
What i like to do is i leave this bromine in the back and i just ignore it.
01:26
And the reason for that is if i go ahead and assign the designation based on the three other substituents that aren't bromine and let's, i'll just give an example.
01:42
I think, you know, obviously this oxygen is the highest priority substituent.
01:45
Next is this carbon that's bound to things.
01:48
And then hydrogen is in third place.
01:52
And if i say determine that, oh, this looks counterclockwise, so that looks like s, because the bromine, the highest priority substitute, or literally any priority substituent besides the lowest is in the back, then that means this is not s, but it is r.
02:12
So i just ignore whatever's in the back, find out what it would be.
02:17
And then i know it's the opposite.
02:19
So here i ignored the bromine.
02:22
It looked like one, two, three was counterclockwise.
02:25
So it looked like s, which tells me it's r.
02:28
And then i don't have to worry about rotating any bonds or swapping any groups.
02:33
And the reason this works is because you can swap groups.
02:38
And every time you do swap a group, it changes the stereochemical designation.
02:42
So if i were to swap the hydrogen and the bromine and put the hydrogen in the back without just rotating everything, it would serve the same purpose as changing the stereochemical designation.
02:54
So this is my little shortcut.
02:57
I just leave things as they are.
02:59
And with that, i have determined that this leftmost carbon and the first molecule is r.
03:06
And we're going to have to use that same trick for the next one because we've got bromine in the back and not hydrogen.
03:14
But nevertheless, let's go and order the substituent.
03:17
So oxygen is the highest.
03:19
Carbon is the second, and then we've got hydrogen, and this looks counterclockwise to me, which means it looks like s, but it's not.
03:27
It is r, because we don't have the lowest priority substitute in the back.
03:33
Okay, so this first molecule is rr.
03:39
Let's just copy that down up here, r...