Résumé : The following trans 1,2‐diarylethylenes have been synthetized by the Wittig reaction: 1‐(2‐naphtyl)‐2‐phenylethylene (m.p. 149,5‐150°), l,2‐di(2‐naphtyl)‐ethylene (m.p. 257‐258°), l‐(2‐naphtyl)‐2‐(3‐pyrenyl)‐ethylene (m.p. 178‐179°), l,2‐di(3‐pyrenyl)‐ethylene (m.p. 306,5–308°). The I. R. spectra of these hydrocarbons exhibit a band between 970 and 950 cm‐1 (out of plane rocking) caracteristic of trans 1,2‐diarylethylenes. 1, 2‐di(3‐pyrenyl)‐ethylene has a U.V. spectrum similar to the U.V. spectra of the 1,2‐dinaphtylethylenes (α, α‐,α. β‐, β, β‐isomers) with a maximum at 330 mμ. Copyright © 1960 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim