Draw a perspective formula for each of the following:
a...

Question

Draw a perspective formula for each of the following:

a. (S)-2-chlorobutane

b. (R)-1,2-dibromobutane

Accepted Answer

Hello everyone. Let's do this problem. It says draw perspective formulas consistent with the compound names given below. Those names are A R Butin to all and B S 23 di chlor oh two methyl hexane. So perspective formula is basically the structure and we want to show the perspective. So the spatial arrangement of those atoms. So including wedges and dashes, for example. So I notice in our names we are given R and S configuration. So that tells me we are going to need to use our con in gold pre log nomenclature rules which tell us how to determine RNS configuration. So first in this system are Cairo carbon will have four different groups, right? So we want to first assign priorities of those four different groups and we do that by atomic mass. So the higher the atomic mass, the higher the priority. And we start by looking at the atom that's directly connected to the carroll center. But what if those atoms are tied? What if they are the same? Well, then we simply move on to the adjacent atoms and use our same rules priority by atomic mass. Well, what if we have a double bond or a triple bond. Well, then we simply count that atom multiple times. So for a double bond, we count that Adam twice. For a triple bond, we count that Adam three times. So that means if we have a carbon double bonded to an oxygen, for example, that's the same as counting a carbon with two oxygen atoms bonded to it. Okay. So once we have our priorities assigned, then we're almost ready to determine art or S configuration. But we need to look at the orientation of our lowest priority group. So is our lowest priority group wedge or is it dash, this will change the rubric for how we decide R and S configuration. And we do that by drawing a circle connecting groups 1 2 and three. And we see if they are, if that circle is going in a counterclockwise direction or in a clockwise direction. So if group number four is wedge, then groups 12 and three going counterclockwise will be our configuration clockwise will be S configuration. And the opposite is true for when group number four is dash counterclockwise will be s clockwise will be our. Okay. So let's apply these rules in addition to what we know about naming to draw structures for these compounds. So first we have our Butin two all. So our route is Butte Butte means four carbons and it's Butin. So that means they're all single bonded to each other. And we have an alcohol group, Which is denoted with the all ending. And that's on carbon # two as listed right before that ending. And we have an R configuration which is not specified. So that means we only have one carbo carbon in our compound. So let's draw this out to see where it is. So four carbons, 1, 23, 4, An alcohol group on carbon # two. And that's it. So our Cairo carbon has to be the one with the alcohol group, right? Because there's also a hydrogen. So there's a hydrogen and alcohol, a ch three group and ch two ch three group. So let's say this alcohol is which and we make our group for our hydrogen dashed. So I'm getting ahead of myself. Hydrogen is always lowest priority, right? So let's start numbering our priorities. Hydrogen is lowest priority for alcohol is going to be the highest priority. Now, we have two carbon groups. The carbon group that is attached to another carbon is going to be next highest priority and the methyl group Is the carbon with three hydrogen. So that's going to be priority number three. So if we connect groups 12 and three, now that circle is going clockwise and since our group number four is dashed, clockwise is going to be our configuration. So this is the structure that we want, right? We wanted our configuration. So I'm going to redraw it without all the arrows and numbers on it. So our wedge alcohol group On Carbon # two. And that is the structure or the perspective formula for. Are you tend to all? Alright, let's repeat this for B for part B we have S die chlor oh two methyl hexane. Alright, starting at the back end with our route, we have hexane which is a six carbon chain. We have a methyl group on carbon number two and two chlorine atoms, one on carbon two and one on carbon three. And we again have one Carvel center which will have s configuration. So let's draw this out to see where that carbon carbon is. So a six carbon chain 123456. And we have a methyl group and a chlorine atom on carbon number two And another chlorine atom on carbon three. So where's archival center? It's going to be on carbon number three, right? There's a chlorine and also a hydrogen. So let's make the chlorine wedge our hydrogen dash. We'll try that. And then we have two different carbon groups. And this carbon carbon number two has these three groups on it, but the methyl groups are two of the same groups. So there's no certain stereo chemistry here that they can rotate freely and it won't change the configuration of anything. So let's check the configuration for this structure, make sure it's s so chlorine will have highest priority. Hydrogen is the lowest priority. Our carbon with the chlorine atom is going to have a higher priority than the carbon that has two hydrogen. So there are our priorities connecting groups 12 and three, those are going counterclockwise and we have our group number four dashed. So that is in fact, s orientation. So let's redraw this a little more clearly. Mhm We have our chlorine on carbon two in our wedge In our methyl on that carbon as well. And then our wedge chlorine on carbon number three. So that is s 23 die chloral to me, Ethel Hex scene. So these are the correct answers which makes see the correct answer choice for this problem. That's it for this one. I hope this video is helpful and thanks for watching.

Draw a perspective formula for each of the following:
a. (S)-2-chlorobutane
b. (R)-1,2-dibromobutane

Key Concepts

Stereochemistry

Chirality

Perspective Formula

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