Three methoxy-substituted 5,7-dihydrodibenzoxepines have been prepared, each in both enantiomeric forms: (-)- and (+)-5,7-dihydro-1,3,9,11-tetramethoxydibenzoxepine (12) starting from, respectively, (+)- and (-)-4,4',6,6'-tetramethoxydiphenic acid (16); (+)- and (-)-5,7-dihydro-1,2,10,11-tetramethoxydibenzoxepine (13) from, respectively, (+)- and (-)-5,5',6,6'-tetramethoxydiphenic acid (25); and (R)-(+)- and (S)-(-)-5,7-dihydro-1,2,3,9,10,11-hexamethoxydibenzoxepine (14) from, respectively, (R)-(+)- and (S)-(-)-4,4',5,5',6,6'-hexamethoxydiphenic acid (30).The previously unpublished resolutions of 4,4',6,6'-tetramethoxydiphenic acid (16) and 5,5',6,6'-tetramethoxydiphenic acid (25) are described.Racemisation parameters for the three 5,7-dihydrodibenzoxepines have been determined and are compared with those for 5,7-dihydro-1,11-dimethoxydibenzoxepine (11).The buttressing effects of the meta-methoxy substituents, and the electronic effects of the para-methoxy substituents on the optical stabilities of the 5,7-dihydrodibenzoxepines are discussed, as are the u.v., and 1H and 13C n.m.r. spectra of these bridged biphenyls.