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The reactions of a set of organoalkaline compounds with trans-p-carotene (Car) were studied in solution (using UV/Vis, ESR, and mass spectroscopy) and compared with the reactions of the same set with insoluble polyacetylene. It was shown that the naphthalene radical ion and the dicarbanionic dimer of 1, I-diphenylethylene, 1,1,4,4-tetraphenyl-l,4-butanediide, react with Car by a simple electron transfer leading to Car radical ion and dianion. This dianion is protonated by methanol mainly at carbon 7 or 7'. On the contrary of diphenylalkyllithium compounds add to Car double bonds. This addition of I mol of diphenylalkyllithium per Car takes place mainly at the central double bond. sec-Butyllithium (sec-BuLi) reacts also by addition to Car. The addition products are in some cases instable and decompose to radical ions through a non-elucidated mechanism. These transfer or addition reactions with Car, as well as the exclusive electron transfer observed with polyacetylene, are rationalized on the basis of the relative redox potentials of reactants. a) Part I : cf.".

It is shown that the mechanism of polyacetylene (PA) reduction (or n "doping") by alkaline carbanionic salts and butyllithium is a simple electron transfer without addition. In this reduction reaction the dicarbanionic dimer of 1 ,I-diphenylethylene (DD2-N%+ ) is quantitatively converted to 1,1 -diphenylethylene. The reduction by 3-methyl-1, 1 -diphenylpentyllithium produces free radicals which deactivate in solution by coupling and disproportionation. But the strong dependence of the ratio of disproportionation to coupling of these radicals on solvent polarity is unusual: no coupling is observed in diethyl ether or pentane, while it is the most important reaction in THF. sec-Butyllithium in pentane also reduces PA by a simple electron transfer process. The "doping" levels can be deduced accurately from the quantitive analysis of the by-products by gas chromatography. R -An electron is transferred from the carbanion to PA with formation of a free radical which reacts rapidly in solution leading to by-products. Several points concerning this process have to be examined:-Are there any secondary reactions such as direct addition of carbanions to double bonds, metalation of PA by H exchange, or reaction between polymer and free radicals? (Such reactions may shorten the length of conjugated double bond sequences).