Polyynes: Possible Bulk Synthesis and Chemical Properties - Polyynes: Synthesis, Properties, and Applications - page 427

FIGURE 18.7 Electronic absorption spectra in n-hexane. (A) Polyyne solution as
prepared. (B) Ene-ynes solution after 5min reduction of polyynes with Zn/HCl.
(C) Ene-yne solution after prolonged treatment with Zn/HCl. (D) Ene-yne solution
left overnight in contact with Zn/HCl solution. (E) Difference spectrum between
ene-yne solution and original polyyne solution.

the electronic absorption spectrum of isomycomycin [23,26] which is a
diene-tryne with the structure [26]

CH 3 C C C C C C CH ¼ CH CH ¼ CH CH 2 CO 2 H

whose spectrum is characterized by three intense bands at 246, 258, and
267 nm followed by other four less intense bands at 288, 306, 324, and
347 nm. If we compare the position of these bands with those reported in
Figure 18.7(B), we can see that the agreement of the first three with those in
Figure 18.7(B) is good (246, 255, and 265 nm) while it is less good for the
other four bands at longer wavelengths. Thus, we can deduce that one of
the main components of the ene-yne mixture produced by the polyyne
reduction is made by a chromophore similar to that present in isomyco-
mycin and composed of three acetylenic bonds and two ethylenic bonds or