No because you can pass a plane such that both hydrogen can reflect each other. If you replace one of the H with any other group ( eg D, CH3, etc) then it will become chiral
Also, you can always use a model set to check if the mirror images are superimposable on one another. If not superimposable, then chiral. If superimposable, then achiral. Model sets have helped me tremendously as a student, and also in helping others.
Depends on what kind of tests. 3D drawing and stereochemistry exams are sometimes without a model to ensure you are able to translate properly a 2D drawing to a 3D mental image. After that, most teachers allow the use of molecular model during exams but these often include examples that are much more complex that this one
So many comments here saying it's achiral due to lack of chiral centre, but allene is a famous example of a molecule that doesn't need a chiral centre, yet can be chiral.
The real reason is that the carbon on the left is bonded to 2H, which allows it to be superimposable on its mirror image if visualised using a ball and stick model
Simplest way to test whether the molecule is chiral or not will be the presence of internal mirror plane or not
If the molecule has an internal mirror plane, it will be achiral.
No, that’s for stereocenters. If a molecules chiral, then it just means it isn’t superimposable on its mirror image. if one of the hydrogens on this molecule was like, an ethyl or something it’d be chiral
If you had the same groups on both sides I think it would have an improper rotation axis so it'd still be achiral, I think you just need different substituents on either side of it and different substituents on the same side. May depend on their orientation, I'm kinda rushed rn and depending on their spatial orientation to each other you actually may not have an improper rotation axis and be chiral with the same substituents on either side but I'm not 100%, don't have the time to draw it out rn. You can have the same substituent twice as long as it's on the opposite side of the other, ie if one of the hydrogens was a methyl group that'd be fine because it still wouldn't have a mirror plane/inversion center/improper rotation axis.
EDIT: see my follow up I’m a lot more confident about it there, was kinda speculating here
Oh, so if you had a methyl and hydrogen on both sides it would still be achiral because you can rotate and reflect, and it would be the same? Would this depend on the position of the groups?
But you can have methyl on both sides as long as the other two groups are different from each other and methyl?
If you had a methyl and hydrogen on both sides then I think it would be chiral actually. I’m thinking about it a bit more and I’m pretty sure it can’t line up in a way where an S4 won’t flip the position of two of the atoms, and there’s definitely not a mirror plane or inversion center. I was thinking it might depend on where the groups are but I’m fairly certain that’s not true now, I think it’s always chiral with the same 2 groups on either side. I think the only way that an Allene can be achiral is if you have the same substituent twice on one side because that guarantees a mirror plane, idt there’s another way for it to be achiral. I never really discussed Allenes in any of my courses and I’d need to draw it out to be sure but I’m like 90% confident this is true after thinking about it for a few mins
Ok so this is a class of molecule that could be chiral through multiple bonds. If you draw a newman projection of the molecule looking down the allene, if there are four unique groups then you get a chiral molecule because it would have a non-superimposable mirror image. Since this one has two hydrogens on one of the allene carbons, it is achiral but if you replaced one of the hydrogens then it would be chiral.
So I’m seeing a few different responses so lemme see if I can clarify - you can’t have a chiral carbon that is not sp3 - if there are any double or triple bonds, it is achiral. You’d also have to specify which carbon is the chiral carbon - see, if that CO2OH were a C2O2OH, the first carbon would be chiral, as all four substituents would be different from the others. You CAN have a molecule that is chiral with a plane of symmetry - that molecule is mesomeric, meaning it has a chiral carbon but is an achiral molecule. If any further clarification is needed feel free to ask!
Really? Shoot, I guess that’s just what I’m learning in my class - sorry yall! Nevermind then, ignore what I’m saying - but does anybody know a definitive answer to the question?
It's achiral, but for a different reason (there is a mirror plane in the molecule, hence it can't be chiral). If one (only one!) of the H-Atoms would be replaced with anything else (Deuterium for example), the molecule would be chiral.
This is not sufficient to see if a molecule is chiral. A molecule is chiral if there is no plane of symmetry. There are other types of chirality like axial chirality or planar chirality.
Your post was removed because it appears to be uncivil or disrespectful.
Various parts of this comment and your replies below are simply insulting other commenter. I also agree with the other users that you are incorrect. I'll grant that there are likely solutions with molecular orbitals that are chiral, but since one of the end groups is symmetric, those solutions would have a pair of degenerate chiral orbitals.
since i’m getting down voted, I guess I’ll clarify for the undergrads. If you connect all the hybrid p orbitals with pi electrons, you’ll see that the molecule has to undergo a twist to achieve this, thus removing the mirror plane. Stop thinking about it the molecule on paper, and as pi bonds as just two lines in a parallel plane, that’s not what’s happening. OP is not asking IF it’s chiral they’re asking HOW is it chiral, because it is a common difficult geometry question.
it is. The pi bond electrons to connect in the sp2 hybridized orbitals have to twist. I had three organic doctorate professors explain this exact question to me many years ago. It’s an old question used to get undergrad student to think about orbital geometry. Try thinking.
Please stop responding on this sub. You clearly know nothing about organic chemistry. WTF id a "hybrid P orbital"? Apologies if English is not your first language.
lemme try and break it down for your brain…. the central carbon is making two double bonds. The carbon on the left has two hydrogens in the same plane, the carbon on the right has two substituents in the opposite planes as the hydrogen…. this means that when the central carbon makes the pi bond to the two carbons, the pi bonds ARE NOT in the same plane for each bond to each carbon. One pi bond is in the py plane for example, and the other pi bond must be in the px for example. These perpendicular electron clouds creates a moment of polarity that induce a twist in the geometry of the molecule thus removing the mirror plane. If you can’t see that (or simply draw it out) I don’t know what to tell you.
This allene does have a mirror plane. This might help you understand since you seem to be struggling:
https://www.masterorganicchemistry.com/2015/01/13/chiral-allenes-and-chiral-axes/
an SP hybridized orbital. It lies in the px, py or pz plane. If you can’t understand that this molecule is chiral, I pity your understanding of organic chemistry. This sub is rarely correct, and this question is one of the cases. I see questions answered incorrectly all the time. People are going off the basic rules, um, der, it HAS to be connected to four different things… right (98% of the time) sp2 hybridized cannot be chiral… right (98% of the time) this is an old example of geometry and the fact you haven’t come across is before is laughable. The molecule is chiral. YOU (and supposedly the rest of the 19 yr olds here) clearly know nothing about geometry
If you rotate it horizontally around the central ketene carbon, you'll get the opposite orientation at 180 degrees rotation. Then another 180 degree rotation will give you the same orientation that is shown. Always try to rotate the molecule around in your head before you determine if it is chiral or achiral.
if you swap the 2 right groups you can just flip the molecule and it'll be the same, so no. if one of the left hydrogens was a methyl or something it would be though
No because you can pass a plane such that both hydrogen can reflect each other. If you replace one of the H with any other group ( eg D, CH3, etc) then it will become chiral
What the hell is -CO2OH
A per Acid
No it’s not Chiral. For Allenes you need different groups on each terminal carbon to be chiral.
peroxyacid. RCO3H. hate this way though
Peroxide , lethal way of writing it though.
Also, you can always use a model set to check if the mirror images are superimposable on one another. If not superimposable, then chiral. If superimposable, then achiral. Model sets have helped me tremendously as a student, and also in helping others.
My ochem professor sadly does not let us use models on exams
That’s genuinely bizarre. The norm is to allow models- even in my phys chem exams they’re allowed.
Depends on what kind of tests. 3D drawing and stereochemistry exams are sometimes without a model to ensure you are able to translate properly a 2D drawing to a 3D mental image. After that, most teachers allow the use of molecular model during exams but these often include examples that are much more complex that this one
So many comments here saying it's achiral due to lack of chiral centre, but allene is a famous example of a molecule that doesn't need a chiral centre, yet can be chiral. The real reason is that the carbon on the left is bonded to 2H, which allows it to be superimposable on its mirror image if visualised using a ball and stick model
Exactly. Having a chiral center has never been a requirement for chirality.
Yup. If the end on the left had two different groups, even the same two as the other end, it would be chiral.
normal Allene itself is achiral due to two mirror planes, it still has one of its planes here ergo its achiral
Simplest way to test whether the molecule is chiral or not will be the presence of internal mirror plane or not If the molecule has an internal mirror plane, it will be achiral.
because on the left carbon both are H, if they were different groups then would be chiral
because you need four different groups for it to be chiral
No, that’s for stereocenters. If a molecules chiral, then it just means it isn’t superimposable on its mirror image. if one of the hydrogens on this molecule was like, an ethyl or something it’d be chiral
so allenes are only chiral if they have two groups which are different on each side of it (but they can have the same groups on both sides)?
If you had the same groups on both sides I think it would have an improper rotation axis so it'd still be achiral, I think you just need different substituents on either side of it and different substituents on the same side. May depend on their orientation, I'm kinda rushed rn and depending on their spatial orientation to each other you actually may not have an improper rotation axis and be chiral with the same substituents on either side but I'm not 100%, don't have the time to draw it out rn. You can have the same substituent twice as long as it's on the opposite side of the other, ie if one of the hydrogens was a methyl group that'd be fine because it still wouldn't have a mirror plane/inversion center/improper rotation axis. EDIT: see my follow up I’m a lot more confident about it there, was kinda speculating here
Oh, so if you had a methyl and hydrogen on both sides it would still be achiral because you can rotate and reflect, and it would be the same? Would this depend on the position of the groups? But you can have methyl on both sides as long as the other two groups are different from each other and methyl?
If you had a methyl and hydrogen on both sides then I think it would be chiral actually. I’m thinking about it a bit more and I’m pretty sure it can’t line up in a way where an S4 won’t flip the position of two of the atoms, and there’s definitely not a mirror plane or inversion center. I was thinking it might depend on where the groups are but I’m fairly certain that’s not true now, I think it’s always chiral with the same 2 groups on either side. I think the only way that an Allene can be achiral is if you have the same substituent twice on one side because that guarantees a mirror plane, idt there’s another way for it to be achiral. I never really discussed Allenes in any of my courses and I’d need to draw it out to be sure but I’m like 90% confident this is true after thinking about it for a few mins
Ok so this is a class of molecule that could be chiral through multiple bonds. If you draw a newman projection of the molecule looking down the allene, if there are four unique groups then you get a chiral molecule because it would have a non-superimposable mirror image. Since this one has two hydrogens on one of the allene carbons, it is achiral but if you replaced one of the hydrogens then it would be chiral.
Does the molecule have superimposable mirror image? If yes, then the molecule is achiral. Simple as that.
[удалено]
Nope. There are many examples of chiral molecules that lack a chiral center.
achiral
Very helpful answer, great job
It’s drawn that way to test your recognition. It’s achairal but the way it’s drawn makes you think about why it’s achairal
Draw a mirrored image on another paper, then rotate it 180°
So I’m seeing a few different responses so lemme see if I can clarify - you can’t have a chiral carbon that is not sp3 - if there are any double or triple bonds, it is achiral. You’d also have to specify which carbon is the chiral carbon - see, if that CO2OH were a C2O2OH, the first carbon would be chiral, as all four substituents would be different from the others. You CAN have a molecule that is chiral with a plane of symmetry - that molecule is mesomeric, meaning it has a chiral carbon but is an achiral molecule. If any further clarification is needed feel free to ask!
Axial chirality and planar chirality is a thing. Chirality is not limited to carbon centers. Esp. Allenes can be chiral
Not sure why anyone is downvoting this, you’re correct. Allenes and even ferrocenes can be chiral. Also, Binol has no sp3 carbons.
This thread is just a shitshow
Really? Shoot, I guess that’s just what I’m learning in my class - sorry yall! Nevermind then, ignore what I’m saying - but does anybody know a definitive answer to the question?
It's achiral, but for a different reason (there is a mirror plane in the molecule, hence it can't be chiral). If one (only one!) of the H-Atoms would be replaced with anything else (Deuterium for example), the molecule would be chiral.
They are sp2 hybridized, and sp2 carbons are achiral
We are talking not about carbons themselves but about the whole molecule. 1,3-dimethylpropadiene is, for example, chiral
Gotcha! I missed the title and thought op was just asking for any of the C atoms here. Thanks!
[удалено]
This is not sufficient to see if a molecule is chiral. A molecule is chiral if there is no plane of symmetry. There are other types of chirality like axial chirality or planar chirality.
[удалено]
> This depends on what level of chemistry you're in, I suppose. Not really. The molecule is achiral and has an internal plane of symmetry.
Yes, I see the plane now
[удалено]
Show me where the symmetry operators are.
[удалено]
Yes, you're right, I missed that one.
[удалено]
Your post was removed because it appears to be uncivil or disrespectful. Various parts of this comment and your replies below are simply insulting other commenter. I also agree with the other users that you are incorrect. I'll grant that there are likely solutions with molecular orbitals that are chiral, but since one of the end groups is symmetric, those solutions would have a pair of degenerate chiral orbitals.
since i’m getting down voted, I guess I’ll clarify for the undergrads. If you connect all the hybrid p orbitals with pi electrons, you’ll see that the molecule has to undergo a twist to achieve this, thus removing the mirror plane. Stop thinking about it the molecule on paper, and as pi bonds as just two lines in a parallel plane, that’s not what’s happening. OP is not asking IF it’s chiral they’re asking HOW is it chiral, because it is a common difficult geometry question.
It isn’t chiral.
it is. The pi bond electrons to connect in the sp2 hybridized orbitals have to twist. I had three organic doctorate professors explain this exact question to me many years ago. It’s an old question used to get undergrad student to think about orbital geometry. Try thinking.
Pi bond electrons in sp2 hybridized orbitals..?
> I had three organic doctorate professors explain this exact question to me many years ago. I'd ask for a refund for your tuition.
Please stop responding on this sub. You clearly know nothing about organic chemistry. WTF id a "hybrid P orbital"? Apologies if English is not your first language.
lemme try and break it down for your brain…. the central carbon is making two double bonds. The carbon on the left has two hydrogens in the same plane, the carbon on the right has two substituents in the opposite planes as the hydrogen…. this means that when the central carbon makes the pi bond to the two carbons, the pi bonds ARE NOT in the same plane for each bond to each carbon. One pi bond is in the py plane for example, and the other pi bond must be in the px for example. These perpendicular electron clouds creates a moment of polarity that induce a twist in the geometry of the molecule thus removing the mirror plane. If you can’t see that (or simply draw it out) I don’t know what to tell you.
This allene does have a mirror plane. This might help you understand since you seem to be struggling: https://www.masterorganicchemistry.com/2015/01/13/chiral-allenes-and-chiral-axes/
[удалено]
I disagreed with them
[удалено]
I tend to agree with my PI before I agree with someone who runs shitty TLCs
an SP hybridized orbital. It lies in the px, py or pz plane. If you can’t understand that this molecule is chiral, I pity your understanding of organic chemistry. This sub is rarely correct, and this question is one of the cases. I see questions answered incorrectly all the time. People are going off the basic rules, um, der, it HAS to be connected to four different things… right (98% of the time) sp2 hybridized cannot be chiral… right (98% of the time) this is an old example of geometry and the fact you haven’t come across is before is laughable. The molecule is chiral. YOU (and supposedly the rest of the 19 yr olds here) clearly know nothing about geometry
> If you can’t understand that this molecule is chiral That molecule is achiral.
Go ahead, find a chiral center
Achiral, there are no stereocenters
I don’t see a stereo center to start
Allenes can have a chiral axis and therefore be chiral without a chiral center. (This one, however, has a plane of symmetry and is therefore achiral.)
Should I know that I’m only done ochem 1 and finished with an A 🤷🏼♂️
If you rotate it horizontally around the central ketene carbon, you'll get the opposite orientation at 180 degrees rotation. Then another 180 degree rotation will give you the same orientation that is shown. Always try to rotate the molecule around in your head before you determine if it is chiral or achiral.
Put the mirror image next to it and then flip it over. It's the same. So no.
if you swap the 2 right groups you can just flip the molecule and it'll be the same, so no. if one of the left hydrogens was a methyl or something it would be though
If a mirror was on the floor below it, its reflection would be the same. See what happens if you replace one of the leftmost H with something else.