Gen. Chem. isomers

[Gasedo]

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Is there a quicker technique in finding isomers, besides drawing the structures? It is too much time consuming, especially when there are 8 or 9 of them.
Thanks

 

[armorshell]

Is there a quicker technique in finding isomers, besides drawing the structures? It is too much time consuming, especially when there are 8 or 9 of them.
Thanks

You really need to be more specific than just "isomers"

Are you talking about enatiomers, diastereomers, all isomers, conformational isomers, etc...

 

[Gasedo]

You really need to be more specific than just "isomers"

Are you talking about enatiomers, diastereomers, all isomers, conformational isomers, etc...

I was talking about constitutional and conformational isomers. No compound has 8 or 9 enantiomers !

 

[DrBowtie]

n= number of chiral centers

2^n

 

[Gasedo]

n= number of chiral centers

2^n

I am a bit confused with the isomers thing, because I found in some books, that you need to find how many different hydrogens are in the compound and there are going to be that many isomers.
For example, 2-methylbutane has 4 different H, so it means there are 4 isomers. But if I apply what you were saying, it is just one chiral carbon, so 2^n = only 2 isomers.
Can somebody please clarify on this topic?
Thanks a lot, 😍

 

[RozhonDDS]

I am a bit confused with the isomers thing, because I found in some books, that you need to find how many different hydrogens are in the compound and there are going to be that many isomers.
For example, 2-methylbutane has 4 different H, so it means there are 4 isomers. But if I apply what you were saying, it is just one chiral carbon, so 2^n = only 2 isomers.
Can somebody please clarify on this topic?
Thanks a lot, 😍

yes, and if you had a stereoisomer that had 2 chiral centers (or carbons), than it would have 2^2=4 isomers, or if it has 3 chiral centers it would have 2^3=8 isomers, with n=number of carbon chiral centers

 

[Gasedo]

yes, and if you had a stereoisomer that had 2 chiral centers (or carbons), than it would have 2^2=4 isomers, or if it has 3 chiral centers it would have 2^3=8 isomers, with n=number of carbon chiral centers

In example before, I said if you count the hydrogens you get 4 isomers, but if you count the chiral C, you get only 2 isomers. Don’t you suppose to get the same number of isomers in both cases? 😕

 

[RozhonDDS]

In example before, I said if you count the hydrogens you get 4 isomers, but if you count the chiral C, you get only 2 isomers. Don’t you suppose to get the same number of isomers in both cases? 😕

you dont care about the hydrogens, the only thing you are concerned with his the carbon chiral centers of a stereoisomer

 

[wigglytooth]

double post.

 

[wigglytooth]

you dont care about the hydrogens, the only thing you are concerned with his the carbon chiral centers of a stereoisomer

Isn't the 2^n thing *only* for stereoisomers? Gasedo was talking about constitutional and conformational isomers... Chiral centers don't matter when you're trying to figure out how many conformations of a hexane you can get(there aren't any chiral centers!). I would just draw them out systematically.

 

[armorshell]

I am a bit confused with the isomers thing, because I found in some books, that you need to find how many different hydrogens are in the compound and there are going to be that many isomers.
For example, 2-methylbutane has 4 different H, so it means there are 4 isomers. But if I apply what you were saying, it is just one chiral carbon, so 2^n = only 2 isomers.
Can somebody please clarify on this topic?
Thanks a lot, 😍

First of all, 2-methylbutane doesn't have any chiral centers, the only isomers it has are due to free rotation around the single bonds, or conformational isomers.

To find the isomers you have to draw newman projections. I've never heard of that hydrogen counting method before, but it might work as 2-methylbutane had 4 conformational isomers.

 

[Gasedo]

Isn't the 2^n thing *only* for stereoisomers? Gasedo was talking about constitutional and conformational isomers...

Yes,finally somebody understood my question! 😱

 

[Gasedo]

First of all, 2-methylbutane doesn't have any chiral centers, the only isomers it has are due to free rotation around the single bonds, or conformational isomers.

To find the isomers you have to draw newman projections. I've never heard of that hydrogen counting method before, but it might work as 2-methylbutane had 4 conformational isomers.

Your right it doesn't have any chiral C. 😛
So, the drawing of the isomers is the only option? As I said before, if you need to draw 8 or 9 isomers, it is a lot of time consuming!
For example, propyl nitrite C3H7NO2 has 6 isomers. What would be your most rapid method to count them?

 

[armorshell]

Your right it doesn't have any chiral C. 😛
So, the drawing of the isomers is the only option? As I said before, if you need to draw 8 or 9 isomers, it is a lot of time consuming!
For example, propyl nitrite C3H7NO2 has 6 isomers. What would be your most rapid method to count them?

Like I said, probably drawing them out. There doesn't seem to be a trick here.

 

[Gasedo]

you dont care about the hydrogens, the only thing you are concerned with his the carbon chiral centers of a stereoisomer

This is true for diastereomers, enantiomers but not for conformational and structural (constitutional) isomers.
OK, I am going nuts already.

 

[armorshell]

This is true for diastereomers, enantiomers but not for conformational and structural (constitutional) isomers.
OK, I am going nuts already.

Where is this question even coming from? Never in any of my study material or classes has a questionlike this ever been asked...

 

[Gasedo]

Where is this question even coming from? Never in any of my study material or classes has a questionlike this ever been asked...

What question? You mean to find the isomers for C3H7NO2?
Well, we should be prepared for the worst!Don't we? 😉

 

[armorshell]

What question? You mean to find the isomers for C3H7NO2?
Well, we should be prepared for the worst!Don't we? 😉

That doesn't seem like a question that would be asked, as it really doesn't have anything to do with anything.

Maybe "What is the highest energy conformational isomer of C3H7NO2"

 

[Gasedo]

That doesn't seem like a question that would be asked, as it really doesn't have anything to do with anything.

Maybe "What is the highest energy conformational isomer of C3H7NO2"

What do you mean it really doesn't have anything to do with anything? Of course it does. You can expect to have questions like this on the DAT. They can give you a compound and ask how many isomers it has.