and electronic properties of a molecule may determine the chirality of subsequent chemical reactions on that molecule. This principal is used to design chemical syntheses where one stereocentre is in place and additional stereocentres are required. When considering how two functional groups or species react, the precise 3D configurations of the chemical entities involved will determine how they may approach one another. Any restrictions as to how these species may approach each other will determine the configuration of the product of the reaction. In the case of asymmetric induction, we are considering the effects of one asymmetric centre on a molecule on the reactivity of other functional groups on that molecule. The closer together these two sites are, the larger an influence is expected to be observed. A more holistic approach to evaluating these factors is by computational modelling, however, simple qualitative factors may also be used to explain the predominant trends seen for some synthetic steps. The ease and accuracy of this qualitative approach means it is more commonly applied in synthesis and substrate design. Examples of appropriate molecular frameworks are alpha chiral aldehydes and the use of chiral auxiliaries. Asymmetric induction at alpha-chiral aldehydes Possible reactivity at aldehydes include nucleophilic attack and addition of allylmetals. The stereoselectivity of nucleophilic attack at alpha-chiral aldehydes may be described by the Felkin–Anh or polar Felkin Anh models and addition of achiral allylmetals may be described by Cram’s rule. Felkin–Anh and polar Felkin–Anh model Selectivity in nucleophilic additions to chiral aldehydes is often explained by the Felkin–Anh model (see figure). The nucleophile approaches the carbon of the carbonyl group at the Burgi-Dunitz angle. At this trajectory, attack from the bottom face is disfavored due to steric bulk of the adjacent, large, functional group. The polar Felkin–Anh model is applied in the scenario where X is an electronegative group. The polar Felkin–Anh model postulates that the observed stereochemistry arises due to hyperconjugative stabilization arising from the anti-periplanar interaction between the C-X antibonding σ* orbital and the forming bond. Improving Felkin–Anh selectivity for organometal additions to aldehydes can be achieved by using organo-aluminum nucleophiles instead of the corresponding Grignard or organolithium nucleophiles. Claude Spino and co-workers have demonstrated significant stereoselectivity improvements upon switching from vinylgrignard to vinylalane reagents with a number of chiral aldehydes. Cram’s rule Addition of achiral allylmetals to aldehydes forms a chiral alcohol, the stereochemical outcome of this reaction is determined