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I am looking for the absorption spectrum of linear polyenes (1,3,5-hexatriene, 1,3,5,7-Octatetraene, 1,3,5,7,9-decapentaene, etc..) in the range of UV and Visible light wavelength.

I see the data at the 2nd page of the PDF (*1). In the table, I see the max absorption wave length for hexatriene is 268nm.

name $\lambda_{max}$
ethylene 163nm
butadiene 217nm
hexatriene 268nm
octatetraene 304nm

But I see another webpage(*2) says hxatriene's wave length is 258nm.

The absorbance due to the π – π* transition in 1,3,5-hexatriene, for example, occurs at 258 nm.

Where do you look for linear polyenes absorption spectrum data?

(*1) https://www.chem.purdue.edu/courses/chm424/Handouts/14.2%20Alkenes%20and%20Aromatics.pdf

(*2) https://courses.lumenlearning.com/suny-mcc-organicchemistry/chapter/interpreting-uv-spectra/

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  • $\begingroup$ Hexatriene can exists as cis- and trans-isomers. $\endgroup$
    – Mathew Mahindaratne
    Jan 25 at 2:41
  • $\begingroup$ These are the wavelengths of the maximum of an absorption band so are probably only accurate to a few nm but I found 268 nm for the hexatriene, so 258 could be a typo. $\endgroup$
    – porphyrin
    Jan 25 at 8:40
  • $\begingroup$ @ porphyrin: According to this article, both isomers of hexatriene shows absorbance at $245, 255,$ and $\pu{265 nm}$. $\endgroup$
    – Mathew Mahindaratne
    Jan 25 at 22:20

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