 When one is considering allylic strain, one needs to consider the possible conformers and the possible stereoelectronic demand of the reaction.For example, in the conformation of (Z)-4-methylpent-2-ene, the molecule isn't frozen in the favored conformer but rotates in the dihedral angle around 30° at <1kcal/mol cost.In stereoselective reactions, there are 2 effects of allylic strain on the reaction which is the sterics effect and the electronic effects.