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I have studied that if in a reaction system chiral reactants are absent but chiral products are produced; then all enantiomers of respective diastereomers are produced in equal concentration or a racemic mixture is produced.

But what is the reason behind this 'principle of racemic mixture formation'? Is it simply because as the enantiomers of respective diastereomers have no difference in physical or chemical properties, the reaction system shows no preference to any of them?

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Because the starting material is achiral and the products are enantiomers, the reaction, by symmetry, must proceed via two enantiomeric transition states. Enantiomers have the same energy, so these two transition states have the same energy, so the rate of product formation is the same for both products. Therefore, they will be produced in equal amounts.

However, there is a complication that was not covered in your statement. There are examples of autocatalytic reactions like the Soai reaction where the product aids in catalysis and a tiny random preference for one enantiomer over the other leads to amplification of that preference. This is akin to how life uses preferentially one enantiomer instead of another, since presumably, we started with achiral materials in the primordial soup.

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  • $\begingroup$ My next question would be what's so special in Soai Reaction? $\endgroup$ – Mockingbird Jun 6 '17 at 15:18
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    $\begingroup$ It produces a chiral product that catalyzes the reaction that makes more of that enantiomer. So once you get any imbalance, the imbalance is amplified. It's a chemical version of the Kelvin water dropper except that the end state is reaction completion instead of discharge. $\endgroup$ – Zhe Jun 6 '17 at 15:23

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