AbstractA stereospecific18O‐labelling study shows that thesyn‐hydroxy group is preferentially lost from thesyn, anti‐title diol uponi‐C4H10chemical ionization, indicating occurrence of a stereoelectronic effect in this process. A collision‐induced dissociation study of deuterium‐ and18O‐labelled analogs shows that a symmetrical ether structure is not formed in the above process by an SNi mechanism. This result leads to the conclusion that the stereoelectronic assistance of theanti‐OH group in the loss of thesyn‐hydroxyl is expressed either in a weak transition state interaction or by other processes such as β‐elimination via hydrogen transfer with concomitant d