Symmetry in dimethyl Cyclohexane compunds

[donkeykong1]

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Why does 1,2-dimethyl cyclohexane have enantiomeric [R/S] properties rather than being a meso compound due to apparent symmetry? Are both cis and trans 1,2 dimethyl cyclohexane enatiomeric?

Can't you draw a line of symmetry right through the the two methyl groups?

 

[PiBond]

Why does 1,2-dimethyl cyclohexane have enantiomeric [R/S] properties rather than being a meso compound due to apparent symmetry? Are both cis and trans 1,2 dimethyl cyclohexane enatiomeric?

Can't you draw a line of symmetry right through the the two methyl groups?

the cis isomer is meso due to a plane of symmetry while the trans isomer can have an enantioner (non-superimposable mirror image) given that it has chiral centers and is not meso. the cis isomer has no enantiomer because it's mirror image is the exact same compound.

meso compounds:
1. have an even # of chiral centers and the same # of R & S stereocenters (so does cis 1,2-dimethyl cyclohexane)
2. has an internal plane of symmetry (so does cis 1,2-dimethyl cyclohexane)
3. net optical rotation of zero

does that help?

 

[donkeykong1]

thanks bro, that helped a lot.