[chehemi123]

hey guys,

i am looking for stereoisomers of piperazine, methylpiperazine and dimethylpiperazine.

piperazine has no stereocenter, so there shouldnt be any stereoisomers.

methylpiperazine has got 3 stereocenter, I think ?
Both N-atoms (with the lone pair and 3 different substituents) and the C-atom with the methyl group. So there should be max. 8 stereoisomers. (2³)

dimethylpiperazine has got 4 stereocenter, I think?
Both N-atoms and the 2 C-atoms with the methyl groups. --> 2⁴=16 stereoisomers (max)

How can I find the meso compounds?
Besides, I have to draw these stereoisomers and I have no plan how I can change the N-atoms to R-configuration or S-configuration.

I hope you can understand my question...I am from Switzerland actually and studying in America.

[RaInBowDaSh1488]

You can't apply RS to the nitrogen atoms in piperazine because of nitrogen inversion. I'd think in the case of piperazine you would only need to consider chiral carbons.

[mhanze]

hey guys,

i am looking for stereoisomers of piperazine, methylpiperazine and dimethylpiperazine.

piperazine has no stereocenter, so there shouldnt be any stereoisomers.

methylpiperazine has got 3 stereocenter, I think ?
Both N-atoms (with the lone pair and 3 different substituents) and the C-atom with the methyl group. So there should be max. 8 stereoisomers. (2³)

dimethylpiperazine has got 4 stereocenter, I think?
Both N-atoms and the 2 C-atoms with the methyl groups. --> 2⁴=16 stereoisomers (max)

How can I find the meso compounds?
Besides, I have to draw these stereoisomers and I have no plan how I can change the N-atoms to R-configuration or S-configuration.

I hope you can understand my question...I am from Switzerland actually and studying in America.

There is no such thing as R, S apsolute configuration on nitrogen atom, it has a rapid inversion (umberella effect like ammonia), so you have N-methylpiperazine, R-2-methylpyperazine and S-2-methylpiperazine

[mhanze]

hey guys,

i am looking for stereoisomers of piperazine, methylpiperazine and dimethylpiperazine.

piperazine has no stereocenter, so there shouldnt be any stereoisomers.

methylpiperazine has got 3 stereocenter, I think ?
Both N-atoms (with the lone pair and 3 different substituents) and the C-atom with the methyl group. So there should be max. 8 stereoisomers. (2³)

dimethylpiperazine has got 4 stereocenter, I think?
Both N-atoms and the 2 C-atoms with the methyl groups. --> 2⁴=16 stereoisomers (max)

How can I find the meso compounds?
Besides, I have to draw these stereoisomers and I have no plan how I can change the N-atoms to R-configuration or S-configuration.

I hope you can understand my question...I am from Switzerland actually and studying in America.

There is no such thing as R, S apsolute configuration on nitrogen atom, it has a rapid inversion (umberella effect like ammonia), so you have N-methylpiperazine, R-2-methylpyperazine and S-2-methylpiperazine

[chehemi123]

Thanks a lot... the drawing makes it much clearer!

That means:
no stereoisomers for piperazine.
2 stereoisomers for methylpiperazine (R-2-methylpyperazine and S-2-methylpiperazine).
and 4 stereoisomers for dimethylpiperazine (the two methyl groups are bonded to two different C atoms) I think the methyl groups must be in para- position because dimethylpiperazine is synthesized by 2-chlorine-propylamine.

are there 4 stereoisomers of dimethylpiperazine or are there some meso compounds?

[mhanze]

Thanks a lot... the drawing makes it much clearer!

That means:
no stereoisomers for piperazine.
2 stereoisomers for methylpiperazine (R-2-methylpyperazine and S-2-methylpiperazine).
and 4 stereoisomers for dimethylpiperazine (the two methyl groups are bonded to two different C atoms) I think the methyl groups must be in para- position because dimethylpiperazine is synthesized by 2-chlorine-propylamine.

are there 4 stereoisomers of dimethylpiperazine or are there some meso compounds?

I would say that the last one and the sixth one are messo compounds because they have plane of symetry

[chehemi123]

i am only looking for the stereoisomers of 1,4-dimethylpiperazine.

if the methyl group is bonded to the nitrogen..isn´t it a configuration isomer ?
That means there are max. 4 stereoisomers? doesnt it?
(because of R, S configuration of the C1 and the C4 atoms) ?

[chehemi123]

That means there are max. 4 stereoisomers? doesnt it?
(because of R, S configuration of the C1 and the C4 atoms) ?

do you understand me? i think of RS, SR, RR and SS
RS and SR might be enantiomers (or ar they meso compounds?) and the same with RR and SS..?

[fledarmus]

Correct me if I'm wrong, but I believe 1,4-dimethylpiperazine has both methyl groups attached to the nitrogen atoms. As Mhanze already pointed out, you will not see stereoisomers of these compounds because of the umbrella inversions.

[Dan]

Correct me if I'm wrong, but I believe 1,4-dimethylpiperazine has both methyl groups attached to the nitrogen atoms. As Mhanze already pointed out, you will not see stereoisomers of these compounds because of the umbrella inversions.

This is correct.

chehemi123, 1,4-dimethylpiperazine is:



How are you assigning R/S to this structure?

[chehemi123]

What is the name of the structure if the methyl groups are bonded to C-atoms and in para-position ?

That´s the strucutre I am looking for because this cmpound is synthesized by 2-chlorine-propylamine.
Is such a structure possible? 

[chehemi123]

And there would be 4 stereoisomers of that structure because the 2 C-atoms with the methyl groups are stereo centers, right?

[discodermolide]

Please draw the structure you are referring to.
There is no para position in this molecule.

[chehemi123]

here it is 

[discodermolide]

These are the structures in the second row third and fourth from the left in the answer of mhanze.
So where is the problem here?