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Abstract— Low temperature techniques are used to record spectra of long wavelength absorbing electrochromic species formed from retinol and related compounds. Formation of these electrochromic species is induced either by iodine or trichloroacetic acid which merely act as acids. The electrochromic species are the corresponding carbonium ions of the respective polyenes. The resulting carbonium ions of a given polyene are identical regardless of whether they are formed by iodine or trichloroacetic acid. The molecular structures of the carbonium ions can be written with certainty. Consequently, the exact nature of the π‐electron system in the polyene and its carbonium ion may be elucidated.

Abstract— On irradiation of all‐trans 5,6‐dihydroretinal (I), two opsin‐active isomers are formed. Both these isomers (believed to be the 11‐cis and 9‐cis isomers) individually couple with cattle opsin to form complexes which have maximal absorption at 465 nm. These complexes satisfy all the established criteria characteristic of synthetic visual pigments.

The reactivity of monochloroand dichloroborane with 2-methylpropene, 1-hexene, and styrene in tetrahydrofuran has been investigated. The structures of the intermediate alkylchloroboranes formed in these

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