Topscore #78 Meso Compounds

[TXDDS2014]

Topscore #78 asks which of the following can be meso and the choices are a)cis-1,2-cyclopentanediol, b)trans-1,2-cyclopentanediol, c)2,3-dihydroxybutane, d)A&B, and e)A&C.

Obviously B is incorrect. They say the answer is E but I think it should be only C. For cyclic compounds i was taught that the only way they can be meso is for the substituents to be cis and on odd # carbons. Because if they are on even # carbons one is axial and one is equatorial. What do yall think?

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[tranv117]

you just answered your own question. Look at choice A again. Cis OH-groups on cyclopentane (5 Carbons). There is a line of symmetry so it is a meso compound.

 

[TXDDS2014]

Yes, but one substituent is on Carbon 1 and one is on Carbon 2, which makes one axial-like and one equatorial-like.

 

[hoyas19]

this could be completely wrong but i think because it is a pentane, not a hexane, it doesn't undergo the chair conformations and you therefore wouldn't have to take axial or equatorial into account for this...they are all on the same plane. but again, im not completely sure..

 

[tranv117]

since it is a cis isomer, the two -OH groups would be either ax/ax or eq/eq. Trans -OH on the 1 and 2 carbon would make it ax/eq.