Kfast/kslow

Racemic N-methylimines derived from 4-substituted 1-tetralones were ki-netically resolved by asymmetric hydrosilylation with phenylsilane (1 equivalent) as a reducing agent using the titanocene catalyst (R)-ll (substrate Ti= 100 1) at 13 °C, followed by a workup procedure to afford the corresponding chiral ketones and chiral cis amines with very high enantio- and diastere-oselectivity (Scheme 12) [28], The extent of the enantiomeric differentiation, kfast/kslow was calculated to be up to 114. The ris-selectivity of this reaction was... 

With the water wheel it is not merely a question of one enantiomer reacting and the other one not. It is, rather, a question of one reacting quickly (kfast) and the other reacting slowly (ksk)W). We will see much more of something called the s value later. This is the selectivity factor and is quite simple s = kfast/ kslow or, in other words, the relative rate. Consider two enantiomers of an alcohol being enantioselectively acetylated by some means. One reacts fast and one more slowly. 

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