Topscore OC 100

[wired202808]

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Guys,

Simple and basic Q, if you are NOT provided stereochemistry but given mere mirror images that are NOT superimposable, are you allowed to say these are enantiomers? (there are 2 chiral carbons on and they are mirror images) even thought no stereochem is provided.

I picked Identical compounds as the answer. I can see how it would be enantiomers. I just wanted to double check topscore logic. Thanks.

 

[toothhornet88]

Guys,

Simple and basic Q, if you are NOT provided stereochemistry but given mere mirror images that are NOT superimposable, are you allowed to say these are enantiomers? (there are 2 chiral carbons on and they are mirror images) even thought no stereochem is provided.

I picked Identical compounds as the answer. I can see how it would be enantiomers. I just wanted to double check topscore logic. Thanks.

No you cannot, from my understanding since Enantiomers are STEREOisomers, stereochemistry is required in order to determine if two compounds are enantiomers or not!

 

[wired202808]

No you cannot, from my understanding since Enantiomers are STEREOisomers, stereochemistry is required in order to determine if two compounds are enantiomers or not!

thanks mate, i guess i chop this up to a topscore mistake and will ignore it! as long as my logic is correct for the exam.

 

[toothhornet88]

ughhh... I may actually be wrong about the whole wedge thing! If there is someone who can help with this, it would be greatly appreciated.

So even if you don't have wedges but have stereocenters you can still determine if two compounds are enantiomers or not right?

 

[rmm30]

Guys,

Simple and basic Q, if you are NOT provided stereochemistry but given mere mirror images that are NOT superimposable, are you allowed to say these are enantiomers? (there are 2 chiral carbons on and they are mirror images) even thought no stereochem is provided.

I picked Identical compounds as the answer. I can see how it would be enantiomers. I just wanted to double check topscore logic. Thanks.

What do you mean by "no stereochemistry is provided"? I think SDN could help you out if you wouldn't mind rephrasing.

 

[rmm30]

ughhh... I may actually be wrong about the whole wedge thing! If there is someone who can help with this, it would be greatly appreciated.

So even if you don't have wedges but have stereocenters you can still determine if two compounds are enantiomers or not right?

With out dash wedge, or fischer or some other projection that would allow you to see the orientation in 3 dimensions you can still tell if you have chiral centers. You would NOT be able to determine absolute R and S config though.

 

[wired202808]

With out dash wedge, or fischer or some other projection that would allow you to see the orientation in 3 dimensions you can still tell if you have chiral centers. You would NOT be able to determine absolute R and S config though.

right thats what im saying; there are no wedges of dashes in the picture; so in theory cant you say that they still might have the same exact optical rotation and therefore not enantiomers?

all it shows in the picture are the exact mirror images. both pictures are of a trans 1,3 dimethyl-cyclohexane. but it does not indicate stereochem.

what do u think ?

 

[rmm30]

ughhh... I may actually be wrong about the whole wedge thing! If there is someone who can help with this, it would be greatly appreciated.

So even if you don't have wedges but have stereocenters you can still determine if two compounds are enantiomers or not right?

So the answer to your question would be No. Enantiomers require that their mirror images have opposite configurations at EVERY stereocenter. There is one exception; if the problem tells you what the configurations are.

OP is that what you meant by "stereocenters not provided"?

 

[wired202808]

So the answer to your question would be No. Enantiomers require that their mirror images have opposite configurations at EVERY stereocenter. There is one exception; if the problem tells you what the configurations are.

OP is that what you meant by "stereocenters not provided"?

see the post I just wrote above; trans 1,3-dimethylcyclohexanes. no wedges or dashes provided, just the fact that they are both trans. Thats why I initially thought it was an identical compound, because I remember from Chads quizzes and destroyer, to never assume anything is identical w/o using dashes n wedges to verify R/S configuration.

 

[rmm30]

see the post I just wrote above; trans 1,3-dimethylcyclohexanes. no wedges or dashes provided, just the fact that they are both trans. Thats why I initially thought it was an identical compound, because I remember from Chads quizzes and destroyer, to never assume anything is identical w/o using dashes n wedges to verify R/S configuration.

Yeah your're right. Think about it though. Based on your logic how could you select identical compounds if you don't know configuration? You can't. The answer is enantiomers. It's a logic question. Bc they tell you the molecule is trans you know one methyl grp will be dash and the other will be wedge. Draw it out. Then draw it's mirror right next to it. Then to verify label the stereocenters. I think that's how you can approach it.

 

[rmm30]

The config on one should be RR. The config on the other should be SS. What I'm still confused about is how you know they are mirror images if they are not represented in 3D. Does the problem state something explicitly? I hope we can figure this out bc stereochemistry on DAT isn't diffiuclt and it's free points in this section.

 

[toothhornet88]

With out dash wedge, or fischer or some other projection that would allow you to see the orientation in 3 dimensions you can still tell if you have chiral centers. You would NOT be able to determine absolute R and S config though.

YES THANK YOU!!!! thats exactly what I was trying to say! In order to determine if two compounds are enantiomers of each other you need to know their R/S configurations at the chiral centers. So even if you have the chiral centers but you cannot determined R/S due to no stereochemistry, you cannot determine if they're enantiomers or not!

Thank you rmm30

 

[rmm30]

YES THANK YOU!!!! thats exactly what I was trying to say! In order to determine if two compounds are enantiomers of each other you need to know their R/S configurations at the chiral centers. So even if you have the chiral centers but you cannot determined R/S due to no stereochemistry, you cannot determine if they're enantiomers or not!

Thank you rmm30

Right. But if the question were to show you a picture (with no dashes and wedges or stereochemistry designation) of TRANS 1,3-dimethylcyclohexane and ask you if it's mirror image was an enantiomer you would say YES. Even though they don't give you the dash/wedge you would able to infer it bc the compound is trans. Take a couple seconds and draw it up to confirm it. I think I'm right but I would really like someone else to weigh in here.

 

[wired202808]

Right. But if the question were to show you a picture (with no dashes and wedges or stereochemistry designation) of TRANS 1,3-dimethylcyclohexane and ask you if it's mirror image was an enantiomer you would say YES. Even though they don't give you the dash/wedge you would able to infer it bc the compound is trans. Take a couple seconds and draw it up to confirm it. I think I'm right but I would really like someone else to weigh in here.

They are both trans; not like one is cis and the other is trans. im just confused as to why you can do it that way. I know in theory it makes sense i've just never seen a problem where it was asked to do that w/o providing the R/S config to ensure that you are indeed looking at enantiomers.

 

[rmm30]

They are both trans; not like one is cis and the other is trans. im just confused as to why you can do it that way. I know in theory it makes sense i've just never seen a problem where it was asked to do that w/o providing the R/S config to ensure that you are indeed looking at enantiomers.

"they are both trans" you keep saying they are both trans. Does the problem say that in words? Or are the two molecules depicted as trans (ie w. dashes and wedges)?

 

[wired202808]

"they are both trans" you keep saying they are both trans. Does the problem say that in words? Or are the two molecules depicted as trans (ie w. dashes and wedges)?

hmm it does not say they are trans, but if you look you see one methyl is pointing up and the other methyl is pointing down.

 

[rmm30]

hmm it does not say they are trans, but if you look you see one methyl is pointing up and the other methyl is pointing down.

Are you comfortable assigning R and S yourself? Becuase if you are then you just put them in dash and wedge form yourself. Draw out the molecule putting one methyl as a dash and the other as a wedge. Then draw it's mirror image right next to it. Then you should see RR on one and SS on another making them enantiomers. Is topscore saying they are identical?

 

[AlbinoPolarBear]

Rmm30 is correct.

We have 2 molecules that are mirror images.
These 2 molecules are of trans-1,3-cyclohexane.

These molecules DO have stereochemistry, as it has 2 chiral centres each.

Mirror images of molecules that:
1. have chiral centres
2. are not superimposable

are enantiomers.

 

[rmm30]

Rmm30 is correct.

We have 2 molecules that are mirror images.
These 2 molecules are of trans-1,3-cyclohexane.

These molecules DO have stereochemistry, as it has 2 chiral centres each.

Mirror images of molecules that:
1. have chiral centres
2. are not superimposable

are enantiomers.

Have you seen this topscore problem? How is this molecule represented? Chair, Dashwedge, Hayworth? What I mean is can it be converted to dash wedge so stereochemistry can easily be assigned?

 

[AlbinoPolarBear]

Have you seen this topscore problem? How is this molecule represented? Chair, Dashwedge, Hayworth? What I mean is can it be converted to dash wedge so stereochemistry can easily be assigned?

Don't have topscore anymore, but I know what 1,3-trans-cyclohexane looks like.

It would probably be represented in chair form, so there are no need to do dashes and wedges to represent stereochemistry. We can assign the group priorities, and therefore the stereochemistry in its chair form.

 

[wired202808]

Don't have topscore anymore, but I know what 1,3-trans-cyclohexane looks like.

It would probably be represented in chair form, so there are no need to do dashes and wedges to represent stereochemistry. We can assign the group priorities, and therefore the stereochemistry in its chair form.

here is the link guys, i redrew it plus here is my modified version tell me if i assigned the R/S correctly based on the assumption that the Hs are on the dashes.

 

[AlbinoPolarBear]

here is the link guys, i redrew it plus here is my modified version tell me if i assigned the R/S correctly based on the assumption that the Hs are on the dashes.

wanna upload it to tiny pic big boy? it's not showing up.

 

[wired202808]

here it is fellas

 

[AlbinoPolarBear]

This is 1,4-dimethylcyclohexane.

It is a meso compound.

 

[wired202808]

This is 1,4-dimethylcyclohexane.

It is a meso compound.

im a putz i drew it wrong. please check again. i assigned the R and S since it was not giving in the problem and I assume that the H is on the dash.

 

[AlbinoPolarBear]

im a putz i drew it wrong. please check again. i assigned the R and S since it was not giving in the problem and I assume that the H is on the dash.

Hey, you drew the dashes and wedges wrong. What you drew was the Hayworth projection, in which the groups are either pointing up or down, not with wedges or dashes. If you had a molecular model, it would probably be helpful to see where the groups points in 3D. If you don't know where the groups are in 3D, you would have trouble assigning stereochemistry.

An easier way is to draw the chair form. You can assign the the chirality easier.

In any case, these 1,3-dimethylcyclohexane does have stereochemistry.
THe mirror image also has stereochemistry, which will make these 2 compounds enantiomers.

Hope this clarifies things.

 

[wired202808]

Hey, you drew the dashes and wedges wrong. What you drew was the Hayworth projection, in which the groups are either pointing up or down, not with wedges or dashes. If you had a molecular model, it would probably be helpful to see where the groups points in 3D. If you don't know where the groups are in 3D, you would have trouble assigning stereochemistry.

An easier way is to draw the chair form. You can assign the the chirality easier.

In any case, these 1,3-dimethylcyclohexane does have stereochemistry.
THe mirror image also has stereochemistry, which will make these 2 compounds enantiomers.

Hope this clarifies things.

perfect, so basically the assumption is that if its drawn in the chair conformation and as mirror images with chiral centers then it HAS TO BE Enantiomers correct.

Meaning if the same was done for any other type of structure that was not a cyclohexane, then you would need the stereochem i.e. wedges and dashes.

correct?

 

[AlbinoPolarBear]

perfect, so basically the assumption is that if its drawn in the chair conformation and as mirror images with chiral centers then it HAS TO BE Enantiomers correct.

If the compound is not meso, then yes.

Meaning if the same was done for any other type of structure that was not a cyclohexane, then you would need the stereochem i.e. wedges and dashes.

correct?

Wedges and dashes help to show stereochemistry when you are trying to draw 3D molecules on paper. But if you know how the molecules are oriented in 3D (in this case, the chair form), then wedges and dashes aren't necessary to show stereochemistry.

In any case, you would have to look at the molecules on a case to case basis. You would have to give me an example before I can give you an explanation.

But in general, enantiomers two molecules that:
1) Are mirror images
2) Have stereochemistry
3) Not meso compounds
4) Not superimposable

 

[LetsGo2DSchool]

Good **** Albino.

 

[AlbinoPolarBear]

Good **** Albino.

Trust my **** dude, I have only the best ****.

 

[LetsGo2DSchool]

Trust my **** dude, I have only the best ****.

I know...

 

[wired202808]

Trust my **** dude, I have only the best ****.

good as gold! thanks man! all clear now.