Are conformational isomers stereoisomers?

[EECStoMed]

Are conformational isomers stereoisomers?

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[Dr OCD]

yes

 

[EECStoMed]

yes

Are they diastereomers? Can geometric isomers be enantiomers?

 

[apoptos]

...................

 

[EECStoMed]

It goes like this:

a.

Hmm, that makes sense because Cis/Trans are geometric isomers. Right? and Since conformational isomers are isomers with only a difference around a single pi bond, they are also diasteromer. But I'm also thinking that some geometric isomers can be enaniomers.

 

[christian15213]

Are conformational isomers stereoisomers?

NOOOOO.... Whom ever says this is an.... First off... What is the first thing we need for a stereoisomer... same molecule or comparing two different molecules? IMO... they are the same molecule so the def of them being an ISOMER is kinda counter intuitive. What they do do however is have different confomrations which is sort of what the point of saying they are a stereoisomer. Two bulky CH3 goups interacting are going to cause a repulsion and thus be at a different energy level of that molecule...

 

[EECStoMed]

Ok, now you have me a bit confused. Conformational isomers are isomers with the same bond connectivity but a rotation about a single sigma bond. The definition of a stereoisomer is a molecule with the same bond connectivity, conformational isomers satisfy this criteria. Right?

NOOOOO.... Whom ever says this is an.... First off... What is the first thing we need for a stereoisomer... same molecule or comparing two different molecules? IMO... they are the same molecule so the def of them being an ISOMER is kinda counter intuitive. What they do do however is have different confomrations which is sort of what the point of saying they are a stereoisomer. Two bulky CH3 goups interacting are going to cause a repulsion and thus be at a different energy level of that molecule...

 

[rcd]

Ok, now you have me a bit confused. Conformational isomers are isomers with the same bond connectivity but a rotation about a single sigma bond. The definition of a stereoisomer is a molecule with the same bond connectivity, conformational isomers satisfy this criteria. Right?

Conformational isomers are steroisomers because they meet the stereoisomer criteria, correct.

Here's the classification:
isomers -> stereoisomers -> conformation isomers
as opposed to enantoimers:
isomers -> stereoisomers -> configurational isomers -> enatiomers

 

[EECStoMed]

Conformational isomers are steroisomers because they meet the stereoisomer criteria, correct.

Here's the classification:
isomers -> stereoisomers -> conformation isomers
as opposed to enantoimers:
isomers -> stereoisomers -> configurational isomers -> enatiomers

What are configurational isomers. I haven't heard of that name in either TPR or EK. I mean, I realize that they are enantiomers from your post, but what's the criteria to be a configurational isomer?

 

[MSTPbound]

What are configurational isomers. I haven't heard of that name in either TPR or EK. I mean, I realize that they are enantiomers from your post, but what's the criteria to be a configurational isomer?

I think rcd means "constitutional" isomers, aka "structural" isomers. "Configuration" probably refers to "R" or "S".

 

[jeesapeesa]

yes, they're stereoisomers. check the definition of what a stereoisomer is.

 

[EECStoMed]

I think rcd means "constitutional" isomers, aka "structural" isomers. "Configuration" probably refers to "R" or "S".

Enantiomers are definitely NOT constitutional isomers, i.e. structural isomers. Those have different bonds all together.

 

[QofQuimica]

Are conformational isomers stereoisomers?

You're not going to like this answer, but it depends. Conformational isomers are the same molecule seen in a different orientation. The prototype example we use for sophomore organic is n-butane. (Remember how the methyl groups can be anti versus gauche versus eclipsed?) However, at room temperature, these conformers will interconvert. (In other words, if someone tries to sell you a bottle of anti-butane, don't buy it unless they've cooled it WAAAAAY down.)

On the MCAT, if you have a pair of conformational isomers, the answer could either be that they are conformational isomers (obviously) or that they are the same molecule. Some books may classify them as stereoisomers since they only differ in terms of orientation (as opposed to constitutional isomers, which differ in connectivity), but I don't like that usage. I think it's unnecessarily confusing. That's where rcd is getting the term "configurational isomers" from though. If you go with calling conformational isomers a subset of stereoisomers, then configurational isomers are stereoisomers that cannot be interconverted by rotation around a bond, as opposed to conformational isomers, which are stereoisomers that CAN be interconverted by rotation around a bond.

 

[EECStoMed]

You're not going to like this answer, but it depends. Conformational isomers are the same molecule seen in a different orientation. The prototype example we use for sophomore organic is n-butane. (Remember how the methyl groups can be anti versus gauche versus eclipsed?) However, at room temperature, these conformers will interconvert. (In other words, if someone tries to sell you a bottle of anti-butane, don't buy it unless they've cooled it WAAAAAY down.)

On the MCAT, if you have a pair of conformational isomers, the answer could either be that they are conformational isomers (obviously) or that they are the same molecule. Some books may classify them as stereoisomers since they only differ in terms of orientation (as opposed to constitutional isomers, which differ in connectivity), but I don't like that usage. I think it's unnecessarily confusing. That's where rcd is getting the term "configurational isomers" from though. If you go with calling conformational isomers a subset of stereoisomers, then configurational isomers are stereoisomers that cannot be interconverted by rotation around a bond, as opposed to conformational isomers, which are stereoisomers that CAN be interconverted by rotation around a bond.

Ahhhhhhhhh, I'm hella confused now.

 

[QofQuimica]

Ahhhhhhhhh, I'm hella confused now.

Sorry, dude(tte). I told you that you weren't gonna like that answer. 😉

Ok, think of it this way: conformational isomers are the same molecule, viewed from different ways. They can be interconverted by rotation around a bond, which is how they differ from stereoisomers (aka configurational isomers). If the MCAT asks you what kind of isomers they are, I'd go with either "conformational isomers" if that's a choice, or else "same molecule."

 

[MSTPbound]

Enantiomers are definitely NOT constitutional isomers, i.e. structural isomers. Those have different bonds all together.

You're absolutely right - I should think a bit longer before I post. Sorry for adding to the confusion... I had never seen the term "configurational" myself, so I was trying to make sense of it. I think Q's post was really helpful in this regard.

Good Luck!

-MSTPbound

 

[QofQuimica]

You're absolutely right - I should think a bit longer before I post. Sorry for adding to the confusion... I had never seen the term "configurational" myself, so I was trying to make sense of it. I think Q's post was really helpful in this regard.

Good Luck!

-MSTPbound

Probably rcd is taking Kaplan. They use that classification system. Like I said, I'm not a huge fan of it. I like using the term "stereoisomer" to refer to what they're calling "configurational isomers."

 

[jeesapeesa]

just try to keep it simple for this test.

enantiomers/diastereomers/geometric/conformational isomers are NOT constitutional/structural isomers. so scratch constitutional/structural from our vocabulary. now we're just dealing with the first four.

Stereoisomers have same bonding sequence but differ in orientation of atoms in space, and this can apply to the first four.

rotations about a single bond produces conformational isomers, so comformational isomers can be stereoisomers.

 

[MSTPbound]

Hey EECStoMed, here's a tip that has always helped me when I have an organic chemistry question. When a whole bunch of people start posting stuff in an orgo thread, and it starts to get confusing, and then you get lucky enough for QofQuimica to grace the thread with her presence, just ignore everything else, and study Q's response.

Obviously, I'm heavily biased here because she happens to use my favorite avatar, and I mean nothing personal towards anyone else who posted an answer here, but generally people with PhD's in organic synthesis - and all the more medical students who scored 2 points shy of perfect on the MCAT - know thier 101 organic chemistry pretty well. 😉

Good Luck!




-MSTPbound

 

[rcd]

What are configurational isomers. I haven't heard of that name in either TPR or EK. I mean, I realize that they are enantiomers from your post, but what's the criteria to be a configurational isomer?

I just googled it to be honest . It makes sense though, you have one group for psuedo-ish stereoisomers (conformational isomers, which includes infinite group of isomers per sigma bond), and a separate one for the "real" isomers.

I guess it's not as widely-accepted as google lead me to believe.

 

[jeesapeesa]

Hey EECStoMed, here's a tip that has always helped me when I have an organic chemistry question. When a whole bunch of people start posting stuff in an orgo thread, and it starts to get confusing, and then you get lucky enough for QofQuimica to grace the thread with her presence, just ignore everything else, and study Q's response.

Obviously, I'm heavily biased here because she happens to use my favorite avatar, and I mean nothing personal towards anyone else who posted an answer here, but generally people with PhD's in organic synthesis - and all the more medical students who scored 2 points shy of perfect on the MCAT - know thier 101 organic chemistry pretty well. 😉

Good Luck!




-MSTPbound

he was apparently confused and just needed some clarity. don't confuse brilliance with the ability to teach; i'm new here, so nothing against anybody, just stating that caution. i love sdn because of this very reason: being able to pick at everybody's brain.

 

[MSTPbound]

he was apparently confused and just needed some clarity. don't confuse brilliance with the ability to teach; i'm new here, so nothing against anybody, just stating that caution. i love sdn because of this very reason: being able to pick at everybody's brain.

Don't take it personally jessapessa - I wasn't directing what I said toward you. I've been accused of of being a "Mod-brown-noser"... 😛 . I would deny the accusation, but looking through my posting history, I do see (sparse) evidence for the accusation 🙄 .

For the record - I think most people in this thread... including you (and minus me) - were saying the same things about conformational isomers, and maybe the semantics of it got confusing. I have no misconceptions about the difference between brilliance and teaching ability; I have suffered at the hands of "brilliant" professors who couldn't teach, and have known many great teachers who may not have been as brilliant as they were hard-working... which is nothing to say of my own experience as a teacher of dance, martial arts, and a general chemistry lab, while I'm probably not the brightest around. I happen to think Q covers both areas - brilliance and teaching ability - quite nicely.

Welcome to SDN!

May your stay be as perpetual and addictive as many of ours have proven to be.

Cheers!

-MSTPbound

 

[Foghorn]

Ahhhhhhhhh, I'm hella confused now.

Just think about anti/syn(eclipsed)/gauche conformations, aka Newman projections, between two C atoms connected with a sigma bond.

Stereoisomer = 3D spacial arrangement of substituents on a C atom. Uses R, S designation for a chiral/stereo center or E, Z for a C atom with a double bond.

Enantiomers = Same molecule with the same substituent connectivity on a C atom but 3D spacial rearrangement of (a) substituent(s) gives a mirror image of the molecule.

Edit: For enantiomers, the mirror image of the molecule must be non-superposable. 😀

Diastereomers = Same molecule with the same substituent connectivity on a C atom but 3D spacial rearrangement of (a) substituent(s) doesn't give a mirror image.

Cis/Trans (E, Z) = Diastereomers with the same substituent connectivity on a C atom, containing a double bond, but 3D spacial arrangement is different.

Conformational (anti, syn, gauche) = Diastereomer with the same substituent connectivity on a C atom but rotation of the sigma bond either gives an anti, syn or gauche conformer.

If you notice with enantiomers and diastereomers, you're looking at the 3D spacial relationships of substituents with respect to the C atom that they are directly bonded. With Cis/Trans and conformational isomers, you're viewing the 3D spacial relationships of substituents with respect to two C atoms.

Other terms you'll need to learn are anomers, epimers and meso isomers.

 

[QofQuimica]

Everyone is welcome to post answers to questions here. Contrary to MSTP's effusive praise ( 😳 ), I make plenty of mistakes, and sometimes I'm flat-out wrong about something. I always tell my students that if I say or write something incorrect, they're responsible for calling me on it and keeping me honest. Ditto for y'all. 🙂

 

[Richter915]

Just think about anti/syn(eclipsed)/gauche conformations, aka Newman projections, between two C atoms connected with a sigma bond.

Stereoisomer = 3D spacial arrangement of substituents on a C atom. Uses R, S designation for a chiral/stereo center or E, Z for a C atom with a double bond.

Enantiomers = Same molecule with the same substituent connectivity on a C atom but 3D spacial rearrangement of (a) substituent(s) gives a mirror image of the molecule.

Diastereomers = Same molecule with the same substituent connectivity on a C atom but 3D spacial rearrangement of (a) substituent(s) doesn't give a mirror image.

Cis/Trans (E, Z) = Diastereomers with the same substituent connectivity on a C atom, containing a double bond, but 3D spacial arrangement is different.

Conformational (anti, syn, gauche) = Diastereomer with the same substituent connectivity on a C atom but rotation of the sigma bond either gives an anti, syn or gauche conformer.

If you notice with enantiomers and diastereomers, you're looking at the 3D spacial relationships of substituents with respect to the C atom that they are directly bonded. With Cis/Trans and conformational isomers, you're viewing the 3D spacial relationships of substituents with respect to two C atoms.

Other terms you'll need to learn are anomers, epimers and meso isomers.

Probably the clearest post here, well done.

 

[BrokenGlass]

Everyone is welcome to post answers to questions here. Contrary to MSTP's effusive praise ( 😳 ), I make plenty of mistakes, and sometimes I'm flat-out wrong about something. I always tell my students that if I say or write something incorrect, they're responsible for calling me on it and keeping me honest. Ditto for y'all. 🙂

Effusive or diffusive?

 

[MSTPbound]

Effusive or diffusive?

Effusive. You know, maybe I didn't stop long enough to consider that others might still feel slighted by my earlier post. That was not my intention, and if anyone has taken it that way, then let me offer a sincere apology here.

I didn't mean to belittle anyone else's advice, however I see how it might be difficult to take at least the first part of my post in any other way. So, I'm sorry, and I really hope no one feels discouraged from posting responses to others' questions here, or anywhere else as a result. I am embarrassed about this, so if you still have any personal issues with my post, please PM me and I'll try to respond specifically to your concerns.

Thank you,

MSTPbound.

 

[christian15213]

LOL, to me it was a surprise... the book I grew up on, solomons... Never ever stated anything as the such... conformational isomer and that was it...

So, one day we had a quiz for my Organic 1 students and the choice came up with exactly that and included both conformational and stereoisomers. So, one person put stereo and they got it marked wrong. Then I said, why would you think otherwise? They responded... that is what the professor told us? I started to think... HMMMM That doesn't make any sense... And here is my main point of why I disagree... When you throw in conformational NEWMAN projections you are making an unneccessary complication...

Look at this picture. from Wiki... and as of lately wiki has been ERRKING me with their information and unwillingness to change obviously incorrect information or misleading.

nevertheless look below... Notice everything is compared to TWO molecules. except conformers. they are the same darn molecule. now, albeit when a molecule is a mirror of itself that is obvously a MESO compound. A diastereomer is a little bit trickier because it is a geometric isomer, again, whatever that means, but the point is a Diastereomer exsists in a few different ways. 1. It is a a direct relation ship of one molecule and another, i.e. if you have a 2 chiral center molecule and compare it to another and the configuration's are exactly opposite per chiral center then you have a Diastereomer... i.e. R,R / R,S = diastereomer and R,S / S,R = enantiomer. Easy... 2. Cis / Trans Z/E respectively... Now the trick is nowing this can happen with a cyclo compound as well with a plane of sysemtry causing a cis trans or meso even... 3. The meso is a mirror of itself this can be a two chiral or more centers or a cyclic ring as described previously... If you can fold it and make a perfect match you have a MESO... REMEMBER MESO ONLY deals with ITSELF... it is VAIN... and is a mirror to itself!!! 3. What should be put on this picture is An ANOMER... which for biomolecules i.e. carbohydrates that are hemiacetal or hemiketals they have a mutor rotating end that causes them to be Alpha (down pointing) or Beta (up pointing) This would a classification along side enantiomers and diastereomers. Lastly, there is another division of diastereomer that is called an epimer... This is also important for biomolecules... Remember I said the whole comparison of the R,S S,S bit from above... Well now lets say you have a sugar glucose that has six carbons which 4 are chiral centers. Well when they are all opposite the enantiomer of D-Glucose 2nd to last OH facing the Right, would be L-Glucose 2nd to last OH pointing to the left. If we took one other, any other chiral carbon and flipped it from one side to the other... We would have an diastereomeric Epimer. Remember two divisions of diastereomers are mesos' which are to their own and directly under diastereomer is an epimer.

Do you see that NEWMAN projections are just a freaking WAISTE OF TIME... to be place here... let alone they are hard enough to understand on their own. I still gave him the points off. but he was the smartest kid so he ended up with a great grade overall.

 

[Foghorn]

LOL, to me it was a surprise... the book I grew up on, solomons... Never ever stated anything as the such... conformational isomer and that was it...

So, one day we had a quiz for my Organic 1 students and the choice came up with exactly that and included both conformational and stereoisomers. So, one person put stereo and they got it marked wrong. Then I said, why would you think otherwise? They responded... that is what the professor told us? I started to think... HMMMM That doesn't make any sense... And here is my main point of why I disagree... When you throw in conformational NEWMAN projections you are making an unneccessary complication...

Look at this picture. from Wiki... and as of lately wiki has been ERRKING me with their information and unwillingness to change obviously incorrect information or misleading.

nevertheless look below... Notice everything is compared to TWO molecules. except conformers. they are the same darn molecule. now, albeit when a molecule is a mirror of itself that is obvously a MESO compound. A diastereomer is a little bit trickier because it is a geometric isomer, again, whatever that means, but the point is a Diastereomer exsists in a few different ways. 1. It is a a direct relation ship of one molecule and another, i.e. if you have a 2 chiral center molecule and compare it to another and the configuration's are exactly opposite per chiral center then you have a Diastereomer... i.e. R,R / R,S = diastereomer and R,S / S,R = enantiomer. Easy... 2. Cis / Trans Z/E respectively... Now the trick is nowing this can happen with a cyclo compound as well with a plane of sysemtry causing a cis trans or meso even... 3. The meso is a mirror of itself this can be a two chiral or more centers or a cyclic ring as described previously... If you can fold it and make a perfect match you have a MESO... REMEMBER MESO ONLY deals with ITSELF... it is VAIN... and is a mirror to itself!!! 3. What should be put on this picture is An ANOMER... which for biomolecules i.e. carbohydrates that are hemiacetal or hemiketals they have a mutor rotating end that causes them to be Alpha (down pointing) or Beta (up pointing) This would a classification along side enantiomers and diastereomers. Lastly, there is another division of diastereomer that is called an epimer... This is also important for biomolecules... Remember I said the whole comparison of the R,S S,S bit from above... Well now lets say you have a sugar glucose that has six carbons which 4 are chiral centers. Well when they are all opposite the enantiomer of D-Glucose 2nd to last OH facing the Right, would be L-Glucose 2nd to last OH pointing to the left. If we took one other, any other chiral carbon and flipped it from one side to the other... We would have an diastereomeric Epimer. Remember two divisions of diastereomers are mesos' which are to their own and directly under diastereomer is an epimer.

Do you see that NEWMAN projections are just a freaking WAISTE OF TIME... to be place here... let alone they are hard enough to understand on their own. I still gave him the points off. but he was the smartest kid so he ended up with a great grade overall.

A meso compound isn't a mirror of itself. A meso compound is a molecule with multiple stereocenters but is achiral i.e. optically inactive because the molecule contains an intrinsic mirror plane of symmetry. And Newman projections aren't useless since it is a tool that can be used to detect for the presence of an internal mirror symmetry plane for non-cyclic structures.

 

[Gavanshir]

Quick question:

In immunohistochemistry, why must the secondary anitbody be of a different organism than the primary antibody? Thanks.

 

[Foghorn]

Quick question:

In immunohistochemistry, why must the secondary anitbody be of a different organism than the primary antibody? Thanks.

Mammals don't normally make antibodies against itself otherwise they'd have an autoimmune disorder.

 

[christian15213]

A meso compound isn't a mirror of itself. A meso compound is a molecule with multiple stereocenters but is achiral i.e. optically inactive because the molecule contains an intrinsic mirror plane of symmetry. And Newman projections aren't useless since it is a tool that can be used to detect for the presence of an internal mirror symmetry plane for non-cyclic structures.

dude... how aren't MESO's a mirror of themselves...

And in context to useless... I was referring to the point that putting conformers in a category of ISOMERS is useless / pointless / confusing / shouldn't be there... Not that newman projections are useless...🙂

 

[BrokenGlass]

dude... how aren't MESO's a mirror of themselves...

And in context to useless... I was referring to the point that putting conformers in a category of ISOMERS is useless / pointless / confusing / shouldn't be there... Not that newman projections are useless...🙂

ME SO inactive

 

[Foghorn]

dude... how aren't MESO's a mirror of themselves...

And in context to useless... I was referring to the point that putting conformers in a category of ISOMERS is useless / pointless / confusing / shouldn't be there... Not that newman projections are useless...🙂

*Sigh*
Use a molecular model or draw the different conformers of 2,3-dibromobutane to figure it out. Only 1 conformation/conformer will have the mirror symmetry plane.

ME SO inactive

 

[TheGreatHunt]

They are the same molecule, same connectivity.

My vote is that by classifying them as stereoisomers we make it sound like they have differnt connectivity, regardless of if it is correct or not

 

[Czarcasm]

This thread just hella confused me.

Wonder why nobody made the simple distinction that an isomer is comparing two or more molecules side by side. Constitutional isomers are two or molecules that vary in structure. Stereoisomers are two or more molecules that have the same structure (connectivity) but differ in their 3D orientation (ie. One R or One S; One Cis or One Trans).

There are different variety's of stereoisomers:

Enantiomers - Non-superimposable mirror images
Diasteromers - Non-superimposable non-mirror images

A pair of Cis/Trans isomers for Alkenes and Cycoalkanes fall under the diasteromer category.

For conformational isomers -- that is, single molecules that have the ability to rotate about a single bond and therefore produce several orientations, the molecules themselves are like QofQuimica stated, the same exact molecule regardless. Unlike a pair of enantiomers/diasteromers which are "glued" in their absolute configuations (R/S), conformational isomers vary at any given instant within the SAME molecule. For that reason, I would classify them as conformational isomers or the same molecule, but never stereoisomers.

HOWEVER, if you were to compare two of the same exact molecule in two entirely different orientations at a given time -- you can technically call them stereoisomers of one another (same connectivity, different 3D orientation), but again, conformational isomers is a better choice word.

 

[Blueprint MCAT Tutor]

This is orgo! We need pictures!

Remember that the MCAT is unlikely to try and trick you with some sort of picayune distinction that doesn't matter. To get the questions right, just remember general definitions and remember the "classic examples" and then compare what you're trying to solve to the classic example:

The person above who said the answer to your question is "sort of" is right, but the more important question is this: "How is the MCAT likely to use the word "conformational isomer" and the word "stereoisomer?"

The answer to that question is, I think, much more straightforward than all of the sturm und drang that's been showing up in the thread.

If the MCAT asks you a question or has an answer choice that uses the term "conformer" they're expecting you to know that it's something that you can freely interconvert by rotation around a bond. No bond-breaking to interconvert. At room temperature, the molecule under discussion is sitting in the beaker flipping back and forth. That's it.

If the MCAT uses the word "stereoisomer" they're just checking that you understand that stereoisomers are different than structural isomers. So the bonding's the same in stereo - that's the basic definition and all you really need to know.

Here's a classic example of a context in which they might test that idea: they'll give you the typical keto-enol tautomerism and ask you what kind of isomer it is but not include "tautomers" in the answer choices. They'll expect you to realize that because the bonding has changed, they're structural isomers.

Remember, stay focused on the only thing that matters: How will the MCAT test this concept?

 

[chemtopper]

remember any isomer formed due to different spatial arrangements of atoms and same connectivity are called as stereo isomers ...now Configurational and conformational isomers are two types of stereoisomers ...Configurational isomers are not formed due to rotation around the bond ...they are again of two types ...geometrical and optical ...geometrical isomers are also called as diastereomers because they are steroisomers but are not mirror images of each other...optical isomers are of two types ...enatiomers which are non superimposable mirror images of each other ...diastereoisomers which are non mirror images of each other...
Conformational isomers are 100% stereoisomers in which rotation on the sigma bond is permitted ...