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.

  • 5
    $\begingroup$ 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
  • 3
    $\begingroup$ 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

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.

  • 2
    $\begingroup$ 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

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.