CIS TRANS-ISOMERIZATION OF 2,2'-DIETHYL-5 ,5'-DIMETHOXY-4,4'-BINAPHTHYLIDENE-1,1'-DIONE FROM A RADICAL INTERMEDIATE/

The H-1-NMR spectrum of hyl-5,5'-dimethoxy-4,4'-binaphthylidene-1,1'-d ione (1) shows flat-topped peaks at room temperature. At higher temper atures sharp peaks are observed while at deep temperatures the spectru m consists of two separated sets of lines. We propose a cis/trans-isom erization with coalescence at room temperature. The rate constants of this isomerization were obtained by dynamic line shape analysis, and a n energy barrier of about 74 kJ mol(-1) was calculated. The intermedia te biradical was proved by ESR spectroscopy.