chiral carbons

[Brazen]

I've been struggling with stereochemistry and just want to verify something. This is a question from my head that I think I've come across before (and will something similar again) so if it doesn't make sense then it's my fault.

Anyway, it's my understanding that a molecule containing a benzene ring will NOT have any chiral carbons in the benzene ring because of the double bonds. So in a hexane ring, there would not be any double bonds, so there would be chiral carbons (if attached to another group of molecules as some point in the ring, of course). I think this is a valid example:


C1-C2-C4&#92
&nbsp\-C3-C5-C6-C7OOH

So C1, C2, C3, C4, C5, and C6 are a hexane ring with C7 in a COOH group attached to C6. The chiral carbons would be C2, C3, C4, C5, and C6, right?

 

[Brazen]

hmm, in case it's not obvious, C4 is connected to C6, but the forum takes out the backslash I tried to use to represent the bond.

edit: fixed it with & # 9 2 html code.

 

[Gibsons]

Originally posted by: Brazen
I've been struggling with stereochemistry and just want to verify something. This is a question from my head that I think I've come across before (and will something similar again) so if it doesn't make sense then it's my fault.

Anyway, it's my understanding that a molecule containing a benzene ring will NOT have any chiral carbons in the benzene ring because of the double bonds. So in a hexane ring, there would not be any double bonds, so there would be chiral carbons (if attached to another group of molecules as some point in the ring, of course). I think this is a valid example:


C1-C2-C4
 \-C3-C5-C6-C7OOH

So C1, C2, C3, C4, C5, and C6 are a hexane ring with C7 in a COOH group attached to C6. The chiral carbons would be C2, C3, C4, C5, and C6, right?

I think your C's would be attached to two H's, correct? if so, they aren't chiral.

Also, if you attach the C4 to the C6... what? Wouldn't that make a cyclopropyl ring? (i.e. a triangle of C4, 5 and 6?)

Is there any way you draw this in paint or something and upload the pic somewhere?

 

[Brazen]

Originally posted by: Gibsons

Originally posted by: Brazen
...

So C1, C2, C3, C4, C5, and C6 are a hexane ring with C7 in a COOH group attached to C6. The chiral carbons would be C2, C3, C4, C5, and C6, right?

I think your C's would be attached to two H's, correct? if so, they aren't chiral.

Ah, freaking heck. I lose it in the details. That's right, the carbons would be attached to two Hydrogens and therefore not chiral.

Also, if you attach the C4 to the C6... what? Wouldn't that make a cyclopropyl ring? (i.e. a triangle of C4, 5 and 6?)

Is there any way you draw this in paint or something and upload the pic somewhere?

No, C4 is not attached to C5, just C2. Maybe this is better. Thanks for the feedback.

 

[Paperdoc]

A chiral carbon is one that has FOUR DIFFERENT atoms or groups attached to it so that it is possible to make two versions of it, each a mirror image of the other. There cannot be ANY chiral carbon in a cyclohexane ring, because every carbon in the ring has TWO essentially identical Carbon atoms attached to it! Now, there nay be a chiral carbon attached to the ring as part of a substituent group, but not in the ring itself.

 

[PlasmaBomb]

Originally posted by: Paperdoc
A chiral carbon is one that has FOUR DIFFERENT atoms or groups attached to it so that it is possible to make two versions of it, each a mirror image of the other. There cannot be ANY chiral carbon in a cyclohexane ring, because every carbon in the ring has TWO essentially identical Carbon atoms attached to it! Now, there may be a chiral carbon attached to the ring as part of a substituent group, but not in the ring itself.

This. The ring structure in cyclohexane is symmetrical.

PS. Your numbering is wrong.

 

[polarbear6]

Originally posted by: Brazen
I've been struggling with stereochemistry and just want to verify something. This is a question from my head that I think I've come across before (and will something similar again) so if it doesn't make sense then it's my fault.

Anyway, it's my understanding that a molecule containing a benzene ring will NOT have any chiral carbons in the benzene ring because of the double bonds. So in a hexane ring, there would not be any double bonds, so there would be chiral carbons (if attached to another group of molecules as some point in the ring, of course). I think this is a valid example:


C1-C2-C4
 \-C3-C5-C6-C7OOH

So C1, C2, C3, C4, C5, and C6 are a hexane ring with C7 in a COOH group attached to C6. The chiral carbons would be C2, C3, C4, C5, and C6, right?

Chirality means having all four groups attached to the carbon different !!
In case you haven't noticed hexane has two hydrogens on each carbon

Note: I didn't read other replys !

 

[Ticky]

Cyclohexanoic Acid has 1 chiral center, at the 1 carbon of the ring.

 

[Paperdoc]

Originally posted by: Ticky
Cyclohexanoic Acid has 1 chiral center, at the 1 carbon of the ring.

I don't see why. It has identical -CH2-etc carbons attached on two sides so it does NOT have four different atoms attached to the C1 carbon.

 

[polarbear6]

c7 has a oh and ketone group(carboxylic acid ground)
or c7 has a cooh group attached to it ??

IN THAT CASE its a bit intresting for me.My guess is its a optical active active compound.
Dont excatly remember the reason my lect told me.

Now to think of it I feel I have wrongly remembered it
Like my lect said it takes a year to learn the basics of organic chemistry and just a week to forget

`_
/ \_COOH are you talking about this ?? IMO its called 1 cyclo hexane methoic acid(am
\_/

guessing).

 

[Paperdoc]

I tried to draw cyclohexanoic acid using just text characters here, showing the ring in chair form with the acid group in an equatorial position to reduce steric hindrance. Ain't happenin'!

C1 is the C within the 6-carbon cyclohexane ring that has the subsituent attached to it. That group is -COOH, and the C within that group would be numbered as C7.

To be a chiral carbon the atom it must be part of a group that can be made 2 ways, each a mirror image of the other, that are NOT super-imposable. That is, no matter how you turn the two versions, one is always different from the other in space. Any planar carbon structure (that is, with a linear shape as in triple-bonded C-C like acetylene, or trigonal planar carbon which includes one double C=? bond like the C=O part of an acid group) cannot be made in two mirror image forms. It can only be done when the central C atom has FOUR other atoms attached to it with the bonds directed in space along the axes of a tetrahedron, the way we always think of carbons with only SINGLY-bonded partner atoms. The 3-dimensional shape of the tetrahedron (as opposed to the planar shape of those others) is what makes this possible. For this reason, the C7 (acid group) carbon in cyclohexanoic acid is NOT chiral.

Now, you could take a close look at two forms of cyclohexanoic acid in its "chair" form, with the acid group substituent in the more-stable equatorial location on C1, or with that group in the axial position on C1. These appear different. BUT it takes just two spatial manipulations of a model (and yes, these actually do happen all the time in the real world): invert the chair to its other chair form (this makes the COOH group equatorial), then flip the resulting model over 180 degrees about the long axis of the molecule, and the result is completely super-imposable with the other one. So the C1 also is NOT chiral.

 

[Ticky]

Originally posted by: Paperdoc
I tried to draw cyclohexanoic acid using just text characters here, showing the ring in chair form with the acid group in an equatorial position to reduce steric hindrance. Ain't happenin'!

C1 is the C within the 6-carbon cyclohexane ring that has the subsituent attached to it. That group is -COOH, and the C within that group would be numbered as C7.

To be a chiral carbon the atom it must be part of a group that can be made 2 ways, each a mirror image of the other, that are NOT super-imposable. That is, no matter how you turn the two versions, one is always different from the other in space. Any planar carbon structure (that is, with a linear shape as in triple-bonded C-C like acetylene, or trigonal planar carbon which includes one double C=? bond like the C=O part of an acid group) cannot be made in two mirror image forms. It can only be done when the central C atom has FOUR other atoms attached to it with the bonds directed in space along the axes of a tetrahedron, the way we always think of carbons with only SINGLY-bonded partner atoms. The 3-dimensional shape of the tetrahedron (as opposed to the planar shape of those others) is what makes this possible. For this reason, the C7 (acid group) carbon in cyclohexanoic acid is NOT chiral.

Now, you could take a close look at two forms of cyclohexanoic acid in its "chair" form, with the acid group substituent in the more-stable equatorial location on C1, or with that group in the axial position on C1. These appear different. BUT it takes just two spatial manipulations of a model (and yes, these actually do happen all the time in the real world): invert the chair to its other chair form (this makes the COOH group equatorial), then flip the resulting model over 180 degrees about the long axis of the molecule, and the result is completely super-imposable with the other one. So the C1 also is NOT chiral.

Whoops. I make that mistake with annoying frequency.