12
$\begingroup$

How would you use Fieser-Kuhn rules to calculate the wavelength of maximum absorption for tartrazine?

tartrazine

Fieser-Kuhn rules states that: $\lambda_{max}=114+5M+n(48-1.7n)-16.5\ R_{endo} - 10\ R_{exo}$

  1. What would $M$ be in this example? There aren't any alkyl substituents, but what I'm not sure about ring residues. Would this refer to the $\ce{SO3Na}$ and $\ce{COONa}$?

  2. Would $n$, the number of conjugated double bonds be equal to 12?

conDoubleBondTartrazine

  1. Does Pyrazole count as a ring for $R_{endo}$? So $R_{endo}=3$?

Or would Woodward-Fieser rules be more suitable to use in this scenario?

$\endgroup$
2
  • $\begingroup$ Have a look on mhchem for input of chemical formulae in the body of questions, answers, comments. Said page includes a test drive to familiarize yourself with this tool, too. $\endgroup$
    – Buttonwood
    Mar 4, 2023 at 11:49
  • $\begingroup$ Terminal -SO3Na groups have each two double bonds $\endgroup$
    – Maurice
    Mar 4, 2023 at 12:56

1 Answer 1

2
$\begingroup$

Fieser-Kuhn rules needs to be used to calculate the wavelength in this case, since there are more than 4 conjugated double bonds. Woodward-Fieser rules are only applicable for conjugated dienes and polyenes with upto 4-double bonds or less. [1]

M = 6 (SOONa, SOONa, COONa, 2 N atoms connected by triple bond,N connected to the Benzene sulfinate group)

n=12 as illustrated in the question

π‘…π‘’π‘›π‘‘π‘œ = 3

πœ†π‘šπ‘Žπ‘₯=114+(5*6)+12*(48βˆ’1.78*12)βˆ’16.5*3βˆ’10*0
πœ†π‘šπ‘Žπ‘₯=425.7nm

This calculation matches the experimental data as seen in [2][3][4] which list the πœ†π‘šπ‘Žπ‘₯ value of tartrazine as 425nm, 427nm, 428nm respectively.


References:

[1] Mehta, A. (2015) Ultraviolet-visible (UV-vis) spectroscopy – Fieser-Kuhn rules to calculate wavelength of maximum absorption (lambda-max) of polyenes (with sample problems): Analytical Chemistry, PharmaXChange.info. Available at: https://pharmaxchange.info/2013/05/ultraviolet-visible-uv-vis-spectroscopy-%E2%80%93-fieser-kuhn-rules-to-calculate-wavelength-of-maximum-absorption-lambda-max-of-polyenes-with-sample-problems/ (Accessed: March 4, 2023).

[2]Gobara, Mohamed & Elsayed, Mohamed. (2016). Preparation and Characterization of PANI/TiO2 Composite for Photocatalytic Degradation of Tartrazine Dye. The International Conference on Chemical and Environmental Engineering. 8. 370-389. 10.21608/iccee.2016.35131.

[3] Ayman A. Ali et al. (2020). Spectrophotometric determination of Tartrazine in soft drink powder and pharmaceutical dosage form. Journal of Basic and Environmental Sciences, 7, https://jbesci.org/published/7.2.7.pdf

[4] Gobara, Mohamed & Baraka, Ahmad. (2014). Tartrazine Solution as Dosimeter for Gamma Radiation Measurement. International Letters of Chemistry, Physics and Astronomy. 33. 106-117. 10.18052/www.scipress.com/ILCPA.33.106.

$\endgroup$
2
  • $\begingroup$ References 2 and 4 are identical $\endgroup$
    – Maurice
    Mar 4, 2023 at 12:54
  • $\begingroup$ @Maurice I have now corrected the references. Both the papers 2 and 4 were from the same set of authors so I had pasted same link by mistake. $\endgroup$ Mar 4, 2023 at 13:07

Your Answer

By clicking β€œPost Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.