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I was reading about stereoisomers and I came across a term pseudo chiral centre. I looked up on the net for its definition and found a weird formula for calculating no. of isomers if the compound has a pseudo chiral centre.

I can't understand how to deduce the formula and how to do analytically instead of using the formula in case of complex molecules say of more than 3 chiral carbon atoms.

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    $\begingroup$ Suppose you have the following compound,4-Methylhepta-2,5-diene.The central carbon atom-C 4 is pseudo chiral because it is chiral only when the stereo centers at C2-C3 and C5-C6 are of different configuration other wise it is not chiral $\endgroup$ – Jayadithya Aug 19 '20 at 11:06
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    $\begingroup$ See the gold book definition of pseudo-asymmetric carbon atom. $\endgroup$ – Martin - マーチン♦ Aug 19 '20 at 12:23
  • $\begingroup$ Yes I saw the definition but how to deduce the formula $\endgroup$ – Charlie Aug 22 '20 at 19:18
  • $\begingroup$ It's something dependent on number of stereocentes $\endgroup$ – Charlie Aug 22 '20 at 19:18
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Consider this molecule

Carbon number 4 is a pseudo chiral center because its chirality depends on the chirality of the second and sixth carbons. For example, if the second carbon is S and the sixth carbon is R, then carbon number 4 can be r or s, but if the chirality of the second and sixth carbons are the same, then carbon number 4 is not the chiral center, because it doesn't have 4 different groups around itself.

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    $\begingroup$ When C2/C6 are of different configurations (R/S), C4 will be stereogenic and achirotopic (r/s). When C2/C6 are of the same configurations (R/R or S/S), C4 will be chirotopic and non-stereogenic. There is no r/s assignment. See: ursula.chem.yale.edu/~chem220/chem220js/STUDYAIDS/isomers/… $\endgroup$ – user55119 Oct 8 '20 at 16:25

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