Anomalous ortho-Proton Acidities of the para-Haloanisoles

This communication presents clear evidence for an aryl meta-position acidification effect by a para-situated bromine or iodine substituent. This effect is manifested at the ortho-protons of both para-bromoanisole and para-iodoanisole. There are indications in the computational literature of an meta-position acidification effect provided by a substituent bromine; there is also experimental evidence obtained mostly at cryoscopic temperatures. No conventional electronic effect can account for this acidification. Herein, both experimental evidence and computational justification are presented for this unusual meta-acidification, not only for bromine, but for iodine as well.