RECEIVED AUGUST 24, l9,X The preparation of four, synthetic geometrical isomers of vitamin A aldehyde (identified as all-trnns, h i s , 2,(i-di-cis, Their ultraviolet absorption spectra, infrared spectra and other physical and chemical properties arc A 2,4-di-cis qtructure An all-trans "a-vitamin A aldehyde" was synthesized from Its properties were different from those of the 6-cis and 2,6-di-cis isomers which excluded the possibility that t h e 6;c-is) is described.given. was preferred for it over a possible 2-trans, 4-cis configuration. a-ionone. latter two compounds might be geometrical isomers of a-vitamin A aldehyde.The configuration of a fifth isomer of vitamin A aldehyde, neoretinene-b, was also studied.In the previous paper in this series2 a synthesis of vitamin A is described by which four crystalline geometrical isomers were prepared. These were identified as the all-trans, 2-cis, 6 4 s and 2,B-di-cis forms, according to the following numbering system CHI CHI \ / CH3
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