Tlic stcrcochcniicnl implications of a non-planar configuration of thc fluorcnc ring systcm wcrc first clenrly csprcsscd by Blills, l'nlincr, and Tomkinson (J. Chcrn. SOC., 1024, 125, 23G5), who poiiitcd out that the trriiisition from the diplienyl striictiirc to that of fluorcnc should involvc it distortion of the diplicnyl molecule wliich could bc partly compc~isntcd by inclinntion of tlic plnncs of thc nronintic rings to that of tho fivc-mcmbercd ring. Thc possibilities of stcrcoisomcrisni thus iiitroduccd wcrc discnsscd in grcntcr dctail I,y Kuhn itlid Jacob (Her., 1025, 58, 1432) \rho re-invcstig:ttcd tlic :illeged isonicritlcs of 9-amiiioMiiorcnc, iiutl rcvisctl tlic cnrlicr cspcriiiiciitnl work of Wegcrlioff (Aiiiiitlcii, 1580, 252, 37), licrp (Bey., lSDG, 29, 231), iintl Scliinidt :tnd Stiitzcl (Bcr., 9-aminofluorcnc cxistcd in two distiiict stcrcoisoiiicric β¬orins, ii conclusion whicli was contcstcd by Klicgl, Wiinscli rind Wcigclc (Bcr., 1926, 59, G31), wlio were unablc to tlctcct 111iy diRcrciicc I)etwccn thc coiiipoiinds cl;iimctl t o IIC isomeric. 111 iiivcstigiitions of 9-nminofluorcnc coiifiisioii 11:is l)ccn iiitroduccd by tlic fit rong tcntlciicy of this bosc t o nl)sorb irtmosphcric cnrboii tliosidc with tlic forin:ition of n cnrbainic :wid dcriviitirc, tliiis giving risc to mixturcs of viirying niclting points. The conception of the iiou-plciniir configuration of polycyclic ;uoui:itic systeiiis wits dcvclopcd by Schlcuk ;ind Bcrgiiiaiiii (Annitlcn, 1928, 463, 125), wlio believed thut t h y liiid secured cspcrinicnt 111 cvidcncc of iion-plniiitr coiifigurritioii of dcriviitivcs of niiphtl~aleiic, iiidciic, fiuoreiic, tiiid :inthriicciic. IIowcvcr, this cvidcncc \rits in inaiiy, if iiot in 1111, rcspccts, iiiisouiid, rind hiis brcii iiiiiiiily rcfutcd by subscquciit iiivcstigatioiis (scc, for