2
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The number of optical isomers possible for the given organic molecule is? $\ce{CH_3-C^*H(OH)-CHCl-CH_2Cl}$ (the configuration is fixed at $\ce{C^*}$)

The given answer is 2. The carbon marked with an asterisk is chiral, and the carbon to the right of it is also chiral. Doesn't that give 4 isomers? What does "configuration is fixed" mean?

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2
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The carbon marked with the asterisk cannot change its configuration, for it to be counted as a stereocentre, it must be able to. hence 2 isomers only

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  • $\begingroup$ So we're considering the optical rotation of the carbon which lies next to the one marked with an asterisk? $\endgroup$ – Tapi Dec 30 '19 at 15:51
  • $\begingroup$ Yes. The only chiral atom here is the third C, which is part of the CHCl group. $\endgroup$ – Maurice Dec 30 '19 at 16:23
  • $\begingroup$ Yes, thats exactly what i meant $\endgroup$ – Haha Hahaha Dec 30 '19 at 16:25

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