For each structure,
1. star (*) any asymmetric carbon at...

Question

For each structure,

1. star (*) any asymmetric carbon atoms.

2. label each asymmetric carbon as (R) or (S).

3. draw any internal mirror planes of symmetry.

4. label the structure as chiral or achiral.

5. label any meso structures.

(g)

(h)

Accepted Answer

Hey everyone. Let's do this problem. And says for each of the following structures assign the configuration of each asymmetric carbon determine the structure as Cairo or a Cairo, show any plane of symmetry and label any miso structure. So first to assign the configuration of each asymmetric carbon, we have to use the con in gold pre logged naming system. So an asymmetric carbon means it's going to have four different groups. Right? So the first step is to assign the priorities of those four groups. And by priorities, we mean by atomic mass. So the higher atomic mass gets the highest priority, lowest atomic mass gets the lowest priority. If we have two atoms that are tied like say two carbons, then we'll simply look at the other atoms that the carbon is attached to on both of the carbons. if we have a double bond that's going to count as having two bonds. So say a carbon oxygen double bond, that carbon will be bonded to two oxygen's or that's at least how we count it. Right. A triple bond is the same thing except three times. And then once we have our priorities assigned, we have to assign our or S. So in order to do this, we need to look at the orientation of group number four. So our lowest priority group is it dash or wedge. So in a Fischer projection the vertical groups are dashed and the horizontal groups are wet. So if our lowest priority group is vertical or dashed. And when we connect groups 1, 2 and three. If that direction is counterclockwise, then that will be s configuration If groups 12 and three connect in a clockwise direction, that will be our And if group four is in the horizontal or wedge position, this rubric changes so counterclockwise will be our clockwise will be S In official projection group #4 is usually going to be seen in the horizontal position. Okay, so let's get this started. So our first fisher projection we have CH three, H, B R and B, R H And another CH three group. Okay, so we have two asymmetric carbons here at these intersections. Right? I'm gonna mark one as the red carbon one as the green carbon or Oh, Mark one and 2 or rather Let's do two and 3. Right? 1, 2, 3, 4. Oh, this might get confusing with the priorities actually. So let's number it or label it A and B. Alright. So assigning priorities on carbon A. Well, we know hydrogen is always going to be for the lowest priority bro, mean is going to be number one and then we have two carbons. Right, well this carbon has one carbon, right? It's attached to this central carbon And then three hydrogen and this carbon is attached to bro, me, another carbon. Another carbon. Right? That the central carbon that we're looking at and a hydrogen. So this group is going to be the next highest priority and then that methyl group will be three. So basically the more hydrogen, the lower the priority. Alright, so let's assign priorities for our green carbon or carbon B. So it's the same groups actually. Right? So we get the same priorities. So hydrogen is four, brewing is one that carbon with the three different groups on it is going to be two and the methyl group is going to be three. Okay, so now let's figure out our or s so our group four, our lowest priority groups are in the horizontal position, which means they are wedge. So that is the case for both carbons. So when we connect groups 12 and three for carbon A, it is going clockwise. So that will be the S orientation. And for carbon B or the green carbon when we connect groups 12 and three, it is also clockwise. So it is also s orientation. Okay, now we have to look at the plaintiff symmetry or if it's miso right? The question also asks that, so we don't have any plane of symmetry here. Right? If I draw a line this way, sure, the methyl groups are opposite of each other, but these hydrogen and bromine groups are not and if I draw a line down the middle this way, the groups are not the same on both sides. So there is no plaintiff symmetry and because it is not symmetrical and these Cairo centers are not opposite, this is not a miso compound, right? Because a miso compound has opposite carbo centers. So say one S. M one R. And it is symmetrical. Okay, let's look at compound B. So we have ch two ch three, H B, R N H O H And CH three. Alright, so I'm gonna do the same color coordination. So we have carbon A carbon B. So bro mean is priority number one hydrogen priority number four, I just like to get those out of the way first and again remember what I said about hydrogen. So here this carbon is I just see carbon and hydrogen is right, that's what my I notice is this direction I notice an oxygen. Okay, so this is going to be our next highest priority group and this will be priority number three. Okay, similar thing going here, hydrogen will before oxygen will be one. I see a bunch of hydrogen is this direction? I see a fancy bro me in this direction. So this is going to be my highest priority carbon in this direction and this will be third priority. Okay, so again, our lowest priority groups are wedge Group # four is wedge. So we're using the same little rubric. So connecting groups 12 and three for carbon A. That is going clockwise. So that will be s orientation connecting carbon B groups 12 and three. That is going counterclockwise. So those will be or that carbon is our configuration. Alright. And there is also no plane of symmetry here, which again also means that this is not a miso compound. So, with all of that being said, the correct answer here is choice C. So compound A is Cairo with S. S. Configuration without a plane of symmetry, and it is not miso and structure B is also Cairo with but with S. R. Configuration also no plaintiff symmetry and also not miso. Okay, that's it for this problem. I hope this video is helpful. And thank you guys for watching.

For each structure,
1. star (*) any asymmetric carbon atoms.
2. label each asymmetric carbon as (R) or (S).
3. draw any internal mirror planes of symmetry.
4. label the structure as chiral or achiral.
5. label any meso structures.
(g)
(h)

Key Concepts

Asymmetric Carbon Atoms

Cahn-Ingold-Prelog Priority Rules

Chirality and Meso Compounds

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