Complete the structure of each of these so that it matches the...

Question

Complete the structure of each of these so that it matches the (R) or (S) configuration associated with the name.

(a)

Accepted Answer

Hi, everyone. Let's take a look at our next problem. It says complete the structure of the compound by determining whether the bonds are wedge or dash as indicated by the name. And we're given a bond. This is a cyclops ring. So we're having one double bond and then on the beta carbon. So adjacent to our double bond, we have a substituent chain, that's a bromo methyl. So a carbon bonded to a bromine and the name of this compound is R three. And then in parentheses, bromo methyl cyclops one E and then before I, I have four, multiple choice options showing wedges and dashes in different places before I talk about them, let's number the carbons here. So I can refer to them by number. So I know that my double bond is from carbon 1 to 2. And then we have our substituent chain on carbon three. So I'll just number these to give me those reference points one through five. So now let's look at my multiple choice answers here. So in choice, A, I have a solid wedge from carbon three out to that carbon on the substituent chain. Choice B that same bond is shown by a dash. Choice C I have that bond shown by a dash and then a bond from carbon 3 to 4 shown as a solid wedge. And choice D I just have a dash from carbon three to carbon two. So without even looking at the name, I can actually eliminate two of these structures just by looking at what the structure is like. So in choice D I show a dash going from carbon three to carbon two, but carbon two is a carbon in a double bond, which means it's sp two hybridized and therefore has a trigonal cleaner geometry. So it's all within the same plane and won't have any wedges or dashed. So this is incorrect just without even looking at the name there. And then in choice C I show a dash from carbon three to the carbon in a substituent, but I also show a solid wedge from carbon three to carbon four. Well, this is a single bond. So that's not the issue, but carbon four is not a chiral center. It has two hydrogens and therefore you wouldn't indicate stereo chemistry there because you won't have any stereo isomers differing at that point. So choice C is incorrect just because you don't indicate stereo chemistry when you don't have a chiral center. So now we're down to choices A and B and we know that that carbon three is our one stereo center in the molecule. So we just have to decide will that carbon three bond to the carbon in the chain be wedge or dash. So again, we have our name to determine that I want to erase the numbers from the inside of my molecule. So I have a little space to work with here. How do I use this name? Well, I have in my name, I have the R and we use that R because we know we would number the priority of the groups around our chiral center. And once they're numbered, if the lowest priority group is in the back, lowest in back, then you draw arrows going from 1 to 2 to 3, then if 1 to 3 is clockwise, you have an R arrangement. If 1 to 3 is counterclockwise or it CCW you have an S arrangement and then if the lowest is in the front, so have the lowest priority in the front, it's the opposite. So let's look at that Carol Center. We know we have a hydrogen there one hydrogen since it is a tertiary carbon that hydrogen is obviously going to be our lowest priority. So I'll put H equals lowest and I don't know whether this is in the front and the back. That's part of what I'm trying to determine because I don't know the geometry, I don't know whether that CC bond is wedge or dash, but I know it's R. So I know how my priority groups need to go So let's look at these other three groups and determine what number they are. So I have three carbons. So that's all the same. I need to look at the second atoms they are bonded bonded to and in the chain, I have a carbon bound bonded to a bromine. So that will be priority one. Then in my ring, I've got AC in AC C double bond and I've got AC in AC C single bond. Well, the carbon in the double bond will be priority too because a double bond counts as being bound to two carbons. So it's bonding is CCH where is carbon? Number four is CH H, so that bar that carbon number four is third priority. So what direction are we going when we go from 1 to 2 to 3? Well, we are moving around in a counterclockwise fashion. We are counterclockwise from 1 to 3 but were labeled R. So that means, but R, so that means the lowest must be in the front. So our hydrogen must be in the front and therefore our chain must be in the back. And so our answer is choice B chain shown as a dash bond. Choice A is incorrect because the, if the chains in the front and the hydrogens in the back, this will be the s arrangement. So that's why to is incorrect. So once again, the bond arranged correctly according to the stereo chemistry of this being an R isotope is choice B with just one chiral center and the bond from carbon three going out onto the chain being a dash. So going below the plane of our cyclen ring. See you on the next video.

Complete the structure of each of these so that it matches the (R) or (S) configuration associated with the name.
(a)

Key Concepts

Chirality

Cahn-Ingold-Prelog Priority Rules

Stereochemistry

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