by the Cram polar model. The polar benzyloxy group is oriented anti to the carbonyl to minimize dipole interactions and the nucleophile attacks anti- to the bulkier (RM) of the remaining two substituents. Evans model More recently, Evans presented a different model for nonchelate 1,3-inductions. In the proposed transition state, the β-stereocenter is oriented anti- to the incoming nucleophile, as seen in the Felkin–Anh model. The polar X group at the β-stereocenter is placed anti- to the carbonyl to reduce dipole interactions, and Rβ is placed anti- to the aldehyde group to minimize the steric hindrance. Consequently, the 1,3-anti-diol would be predicted as the major product. Carbonyl 1,2 and 1,3 asymmetric induction If the substrate has both an α- and β-stereocenter, the Felkin–Anh rule (1,2-induction) and the Evans model (1,3-induction) should considered at the same time. If these two stereocenters have an anti- relationship, both models predict the same diastereomer (the stereoreinforcing case). However, in the case of the syn-substrate, the Felkin–Anh and the Evans model predict different products (non-stereoreinforcing case). It has been found that the size of the incoming nucleophile determines the type of control exerted over the stereochemistry. In the case of a large nucleophile, the interaction of the α-stereocenter with the incoming nucleophile becomes dominant; therefore, the Felkin product is the major one. Smaller nucleophiles, on the other hand, result in 1,3 control determining the asymmetry. Acyclic alkenes asymmetric induction Chiral acyclic alkenes also show diastereoselectivity upon reactions such as epoxidation and enolate alkylation. The substituents around the alkene can favour the approach of the electrophile from one or the other face of the molecule. This is the basis of the Houk's model, based on theoretical work by Kendall Houk, which predicts that the selectivity is stronger for cis than for trans double bonds. In the example shown, the cis alkene assumes the shown conformation to minimize steric clash between RS and the methyl group. The approach of the electrophile preferentially occurs from the same side of the medium group (RM) rather than the large group (RL), mainly producing the shown diastereoisomer. Since for a trans alkene the steric hindrance between RS and the H group is not as large as for the cis case, the selectivity is much lower. Substrate control: asymmetric induction by molecular framework in acyclic systems Asymmetric induction by the molecular framework of an acyclic substrate is the idea that asymmetric steric