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According to my chemistry manual meso forms are "a particular case of of stereoisomers" implying that they are isomers, anyway right after this sentence the manual states that if you rotate the 2 forms of tartaric acids (the green ones in the image) you obtain the same molecule... so they're not isomers. Is that correct? Are the green forms the same molecule? In this way it would be senseless to speak about isomers...enter image description here

I'm not asking if these 3 formulas are isomers, because they obviously are. I'm asking whether the green forms (the last 2 forms starting from left) are to be considered isomers (that means they have a different structure) or they are totally (in every aspect) the same molecule with a different drawing.


marked as duplicate by Loong, Jan, Todd Minehardt, M.A.R., ringo Oct 5 '16 at 16:20

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  • $\begingroup$ Everything that's pictured here are isomers. Which of these are different and which are identical is another question. $\endgroup$ – Ivan Neretin Oct 5 '16 at 14:12
  • $\begingroup$ ‘Are meso compounds isomers’ — of what? $\endgroup$ – Jan Oct 5 '16 at 14:39
  • $\begingroup$ Rotate your screen 180 degrees, and you'll see that the left green one is the same as the right green one. They are the very same molecule, one is just drawn upside down. (If you think rotating your screen is somehow an invalid way of thinking about it, you are welcome to rotate your head 180 degrees :D) $\endgroup$ – orthocresol Oct 5 '16 at 16:48
  • $\begingroup$ Also, the linked duplicate already answers this exactly. Did you read the answer? "[...] the meso-compound and its mirror image are not isomers of each other since they are actually the same compound." $\endgroup$ – orthocresol Oct 5 '16 at 17:09