text: Cieplak's proposal is supported by investigating the effects of various electronic substituents on product distribution. By installing an electron-withdrawing substituent such as a methoxy group at the C2 position, the reduction of substituted cyclohexanones begins to favor equatorial attack. This is because the axial C-O bond is a worse electron donor than a C–C bond, so axial attack is less favored. 
  Cieplak also demonstrated this effect by introducing electron withdrawing substituents on C3, which decrease the electron-donating capability of the ring C–C bond and therefore disfavor equatorial attack, which is antiperiplanar to this bond. Electron-donating substituents at C3 subsequently favor equatorial approach, since increasing C–C electron density favors σ donation into σ* and thereby encourages equatorial approach.
  This effect can also be investigated by changing the electronic nature of the nucleophile. In the case of an electron-deficient nucleophile, the σ* of the forming C-Nuc bond is lower in energy and better stabilized by attack antiperiplanar to electron-rich axial C-H bonds. Attack therefore occurs axially. If the nucleophile is electron-rich, however, the donation of more electron density is less favored and equatorial attack may prevail. These trends have been observed even when normalizing for steric bulk of the nucleophile.
  In substituted norbornones, nucleophilic attack will come antiperiplanar to the bonds which can best donate into σ*. The bonds positioned for this interaction are the bridgehead C–C bonds on the six-membered ring. Substituents which donate electron density to these bonds, such as ethyl groups, increase the rate of addition anti to the alkyl groups, which is the antiperiplanar trajectory. If electron-withdrawing substituents such as esters are appended to the C–C bonds, however, the selectivity favors syn addition, so that the bonds donating into σ* are the more electron-rich C–C bonds which are hydrogen-substituted.
  A similar example is seen in substituted 2-adamantones, where varying the electronic properties at the remote 5 position has profound effects on product distribution. A hydroxyl group is able to donate electron density inductively to the forming σ* bond antiperiplanar, so attack from that side is favored. The electron-withdrawing ester substituent, however, lacks this stabilization ability. Instead, the C–H bonds are better electron donors than the C–COMe bonds, so attack comes anti to the hydrogen substituents and subsequently syn to the ester group. This explains the effect of remote electron-donor groups on stereochemical outcomes, which has been difficult to explain with other stereochemical models. The rigidity of the adamantone skeleton allows for tight control of conformation and minimization of competing effects.