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Hello everyone

Name:  fischer projection 1.png
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I don't understand in the last drawing why the -COOH group and why the -CH3 group are placed where they are as wedges and dashed lines.

Why is the COOH group on the left and why is the CH3 group placed on the right hand side? Are allowed to draw those two groups in the opposite way or would that make the tetrahedral molecule incorrect?

I fully understand though why the NH2 group and H group are upwards in the last drawing as the wedges are coming towards us in the second drawing. I've assumed we're looking at the molecule from the top!

Thanks in advance!

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Nirgilis
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(Original post by James A)

Why is the COOH group on the left and why is the CH3 group placed on the right hand side? Are allowed to draw those two groups in the opposite way or would that make the tetrahedral molecule incorrect?
As long as the CH3 is wedged, and the COOH is dashed, it doesn't really matter if they are left or right
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(Original post by Nirgilis)
As long as the CH3 is wedged, and the COOH is dashed, it doesn't really matter if they are left or right
Thanks pal!

What about if the COOH is wedged and the CH3 dashed? Would that cause an issue?
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(Original post by Nirgilis)
As long as the CH3 is wedged, and the COOH is dashed, it doesn't really matter if they are left or right
Ohh wait, is it because the CH3 is at the bottom on the second drawing??

ahhh I think I get it now
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Nirgilis
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(Original post by James A)
Thanks pal!

What about if the COOH is wedged and the CH3 dashed? Would that cause an issue?
That would be a different enantiomer (do the R and S checks on the two molecules)

(Original post by James A)
Ohh wait, is it because the CH3 is at the bottom on the second drawing??

ahhh I think I get it now
:yep: . In the second drawing, you are looking at the molecule from the top, looking down. In the third drawing, you're looking directly at the CH3 group from the second drawing
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(Original post by Nirgilis)
That would be a different enantiomer (do the R and S checks on the two molecules)



:yep: . In the second drawing, you are looking at the molecule from the top, looking down. In the third drawing, you're looking directly at the CH3 group from the second drawing
Cheers for that! Gave you some rep I think!

So I have another question. I saw a molecule on a lecture slide so I copied it down and tried to convert it to a normal 3d wedge and dashed structure. The one on the left shows the H coming towards us and the OH going away from us.

My question is that I drew out the same structure but in a different 3d tetrahedral drawing as the textbook demonstrates. Are these two drawings the exact same structure ,but just viewed in a different orientation??? I find it hard to rotate around 3d images

Cheers pal!!

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Nirgilis
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(Original post by James A)
Cheers for that! Gave you some rep I think!

So I have another question. I saw a molecule on a lecture slide so I copied it down and tried to convert it to a normal 3d wedge and dashed structure. The one on the left shows the H coming towards us and the OH going away from us.

My question is that I drew out the same structure but in a different 3d tetrahedral drawing as the textbook demonstrates. Are these two drawings the exact same structure ,but just viewed in a different orientation??? I find it hard to rotate around 3d images

Cheers pal!!

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Hint for you: Work out the R or S descriptor of all the molecules you've drawn . If the drawings are correct, they should all be the same

Work them out and get back to me if you need more help?
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(Original post by Nirgilis)
Hint for you: Work out the R or S descriptor of all the molecules you've drawn . If the drawings are correct, they should all be the same

Work them out and get back to me if you need more help?
Got both as R!!!! Could you have a look at how I obtained the R configuration in the attachment, please?

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(Original post by Nirgilis)
Hint for you: Work out the R or S descriptor of all the molecules you've drawn . If the drawings are correct, they should all be the same

Work them out and get back to me if you need more help?
I rotated the right hand molecule along an axis to get the Hydrogen atom behind the plane!

*around an axis
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(Original post by James A)
Got both as R!!!! Could you have a look at how I obtained the R configuration in the attachment, please?
:yep: . And since you know they have the same stereochemical descriptor, you know they are the same enantiomer and hence your two drawings are identical! . They are merely rotations of each other

Because you have the right answer, see how I would do it below:

Spoiler:
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(Original post by Nirgilis)
:yep: . And since you know they have the same stereochemical descriptor, you know they are the same enantiomer and hence your two drawings are identical! . They are merely rotations of each other

Because you have the right answer, see how I would do it below:

Spoiler:
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Awesome

Just wondering though, what is the reason for the last part you did where you rotated the molecule 90 degrees?? Cheers bud!
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Nirgilis
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(Original post by James A)
Awesome

Just wondering though, what is the reason for the last part you did where you rotated the molecule 90 degrees?? Cheers bud!
Oh. Just to show you that the way you had drawn it was equivalent to the way I had drawn it . They're all the same
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(Original post by Nirgilis)
Oh. Just to show you that the way you had drawn it was equivalent to the way I had drawn it . They're all the same
Gotcha

Thanks for all the help though, I would be struggling without you to show me the way to my questions!

Thanks again!

btw, I see you do Chemical Biology, is that quite similar to Biochemistry or does it have particular differences???
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(Original post by James A)
Gotcha

Thanks for all the help though, I would be struggling without you to show me the way to my questions!

Thanks again!
Not a problem . Chemistry is a severely under-loved subject, so any help I can give at all

btw, I see you do Chemical Biology, is that quite similar to Biochemistry or does it have particular differences???
Heh. Chemical Biology at Warwick is the only course of it's kind in the country. At Warwick, biochemistry runs as a biology degree, with, maybe 20% chemistry to 80% biology. Chemical Biology is a degree run by the chemistry department instead, running with the opposite ratios (80% chemistry and 20% biology). It's a nice course to do as I get all of the organic, biological, medicinal chemistry, and avoid all the horrible physical chemistry, like quantum, for a few nice biology modules such as enzymes and immunology :yep:

I can't compare it to other biochemistry courses though . Warwick seems to be weird in the way they operate the chemistry and biology courses here :yep:
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(Original post by Nirgilis)
Not a problem . Chemistry is a severely under-loved subject, so any help I can give at all



Heh. Chemical Biology at Warwick is the only course of it's kind in the country. At Warwick, biochemistry runs as a biology degree, with, maybe 20% chemistry to 80% biology. Chemical Biology is a degree run by the chemistry department instead, running with the opposite ratios (80% chemistry and 20% biology). It's a nice course to do as I get all of the organic, biological, medicinal chemistry, and avoid all the horrible physical chemistry, like quantum, for a few nice biology modules such as enzymes and immunology :yep:

I can't compare it to other biochemistry courses though . Warwick seems to be weird in the way they operate the chemistry and biology courses here :yep:
That sounds pretty good to me, I do Pharmacy (1st year at Reading) and it's just a massive relief to not be doing much on physical chemistry, as well as not doing anything related to ecology (which I detested at A-level)
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(Original post by Nirgilis)
Not a problem . Chemistry is a severely under-loved subject, so any help I can give at all



Heh. Chemical Biology at Warwick is the only course of it's kind in the country. At Warwick, biochemistry runs as a biology degree, with, maybe 20% chemistry to 80% biology. Chemical Biology is a degree run by the chemistry department instead, running with the opposite ratios (80% chemistry and 20% biology). It's a nice course to do as I get all of the organic, biological, medicinal chemistry, and avoid all the horrible physical chemistry, like quantum, for a few nice biology modules such as enzymes and immunology :yep:

I can't compare it to other biochemistry courses though . Warwick seems to be weird in the way they operate the chemistry and biology courses here :yep:
Hey again

Quick question.

I'm looking at Conformation isomers and I read that they are stereoisomers that can be converted into another one by rotation around a single bond. So now of course, this could entail anti-periplanar and syn-periplanar .

However could this also include R/S stereoisomers????

Cheers
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Jamerson
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I can't help but feel disappointed that this thread isn't about Jenna Fischer
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Nirgilis
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(Original post by James A)
Hey again

Quick question.

I'm looking at Conformation isomers and I read that they are stereoisomers that can be converted into another one by rotation around a single bond. So now of course, this could entail anti-periplanar and syn-periplanar .

However could this also include R/S stereoisomers????

Cheers
Anti- and syn- descriptors are used to describe the relationship between two molecules. So, as you're probably aware, if group A and B are rotated in such a way that they are 180 degrees from each other, then it's anti-. Have a look at this image to see the two relationships: (shamefully stolen from wikipedia, but look at the relationship between X and H)

Spoiler:
Show



R and S descriptors describe how the atoms are arranged on one stereo-centre. Therefore, the relationship between H on one centre with X on another centre does not change how X and H are arranged on their respective carbons. In the image above, the centre with X on has been rotated. Assume that X is priority 1, R3 is priority 2 and R4 is priority 3 (so the C-C bond is lowest priority and should be facing away from us), work out the R and S descriptors of that carbon in both rotations and see what's up



EDIT: Tip for the future, the word ''stereoisomer'' is a very broad term . It encompasses ''conformational isomer'', ''enantiomer'' and ''diastero isomer'' as well as ''cis/trans isomerism'' . So just be careful of the meaning you are trying to convey, especially in exams :yep:
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I recommend buying a molecular model kit. This is the one I used: http://www.amazon.co.uk/Orbit-Molecu...ular+model+kit

It really helps to make sense of 3d models. At my university we were even allowed to bring them into exams with us (straight chemistry though).
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(Original post by Nirgilis)
Anti- and syn- descriptors are used to describe the relationship between two molecules. So, as you're probably aware, if group A and B are rotated in such a way that they are 180 degrees from each other, then it's anti-. Have a look at this image to see the two relationships: (shamefully stolen from wikipedia, but look at the relationship between X and H)

Spoiler:
Show



R and S descriptors describe how the atoms are arranged on one stereo-centre. Therefore, the relationship between H on one centre with X on another centre does not change how X and H are arranged on their respective carbons. In the image above, the centre with X on has been rotated. Assume that X is priority 1, R3 is priority 2 and R4 is priority 3 (so the C-C bond is lowest priority and should be facing away from us), work out the R and S descriptors of that carbon in both rotations and see what's up



EDIT: Tip for the future, the word ''stereoisomer'' is a very broad term . It encompasses ''conformational isomer'', ''enantiomer'' and ''diastero isomer'' as well as ''cis/trans isomerism'' . So just be careful of the meaning you are trying to convey, especially in exams :yep:
Wicked mate, Chemistry is finally starting to 'click' for me! Stereochemistry at least

(Original post by OMG TOOTHBRUSH)
I recommend buying a molecular model kit. This is the one I used: http://www.amazon.co.uk/Orbit-Molecu...ular+model+kit

It really helps to make sense of 3d models. At my university we were even allowed to bring them into exams with us (straight chemistry though).
That's a good idea, yeah I was thinking of getting a Molymod kit but this one seems better! Cheers dude!
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