[mhanze]

here it is 

[orgopete]

I think this is going to be a complicated reaction. I think you would get all of the structures of mhanze's second row and their enantiomers, though not in equal proportions. I think the starting material must have been racemic. If someone knows how this mustard opens, let them enlighten us.

[chehemi123]

Thats it! great, thank you!

i was just thinking of the number of stereoisomers.
What about (2R,5R)-2,5-dimethylpiperazine and (2S,5R)-2,5-dimethylpiperazine? Are they meso compounds  to (2S,5S) and (2R,5S) ?

[sjb]

Thats it! great, thank you!

i was just thinking of the number of stereoisomers.
What about (2R,5R)-2,5-dimethylpiperazine and (2S,5R)-2,5-dimethylpiperazine? Are they meso compounds  to (2S,5S) and (2R,5S) ?

Meso has a very specific meaning when referring to enantiomers. Whilst the (2R, 5S) compound is identical to the (2S, 5R) compound, the (2R, 5R) and (2S, 5S) are different.

[orgopete]

Don't you think the 2,6-dimethylcyclohexane isomer might be the major product by opening the azeridinium ring at the least substituted carbon? I believe the epoxied opens at the least substituted carbon with nucleophiles.

[chehemi123]

Don't you think the 2,6-dimethylcyclohexane isomer might be the major product by opening the azeridinium ring at the least substituted carbon? I believe the epoxied opens at the least substituted carbon with nucleophiles.

I am not quite good at those reaction speculations  in the task it is said that the product must have: 62.98% C, 12.30% H and 24.72% N.

Meso has a very specific meaning when referring to enantiomers. Whilst the (2R, 5S) compound is identical to the (2S, 5R) compound, the (2R, 5R) and (2S, 5S) are different.

Why are (2R, 5S) and (2S, 5R) indentical?

[sjb]

Sorry, my mistake They are not.

[chehemi123]

No worries! 

That means 4 stereoisomers
is it cis-trans isomerism?

[Dan]

Sorry, my mistake They are not.

I think they are! There is a centre of symmetry. There are 3 stereoisomers of 2,5-dimethylpiperazine: 2R,5R, 2S,5S and 2R,5S (= 2S,5R).

[chehemi123]

the ones you painted: aren´t they (2R,5R) and (2S,5S) ?
'cause both methyl groups come out of the coplanarity ? and both go beyond it ?
Aren´t  (2R,5S) and (2S,5R) the structures in which the methyl groups come both out of or both go beyond the coplanarity?

Sorry I am confused 

[Dan]

the ones you painted: aren´t they (2R,5R) and (2S,5S) ?

No

'cause both methyl groups come out of the coplanarity ? and both go beyond it ?
Aren´t  (2R,5S) and (2S,5R) the structures in which the methyl groups come both out of or both go beyond the coplanarity?

No, that is not the correct method for assigning R/S. Read about the Cahn-Ingold-Prelog priority rules, the assignment of R/S has a precise meaning that you should learn. Example.

[sjb]

Sorry, my mistake They are not.

I think they are! There is a centre of symmetry. There are 3 stereoisomers of 2,5-dimethylpiperazine: 2R,5R, 2S,5S and 2R,5S (= 2S,5R).

Hmm, sits corrected. Had a mental block of meso compounds needing a plane of symmetry. Need to break out those models again

[chehemi123]

ahhh...i got it now...
thanks a lot...

but shouldnt be the 2R5S-2,5-dimethylpiperazine in mhanze's drawing be an 2S5R-2,5-dimethylpiperazine ??

TIA