Although the energy difference between coplanar anisole and its isomer is quite large, the rotation between the O–CH bond becomes favorable when the electronic properties of methoxy group on aromatic rings need to be altered to stabilize an unusual intermediate or a transition state. In the following reaction, the regioselectivity could be rationalized as the out-of-plane rotation of the O–C bond which changes the methoxy group from an in-plane donor group to an out-of-plane acceptor group.
The intermediate of the above reaction is the di-anion and the stereoelectronic effect that stabilizes this intermediate over the other one is the fact that the anionic charge at the para position could delocalize to the oxygen atom via orbital interaction: π(benzene) → σ*(O–CH).