Compare the colors of the product with the starting material. Offer an explanati

Question

Compare the colors of the product with the starting material. Offer an explanation for the difference. Hint: draw the structure of -carotene, the compound that makes carrots orange, and compare it to the structures of 1 (Enol-Form) and 2.

NMR Application to Evaluate the Reduction Product of Curcumin

H2 (g) (xs), 10% Pd/C o 50 90% In this laboratory, you will reduce curcumin (1), the intensely yellow-staining chemical derived from tumeric powder, to tetrahydrocurcumin (2) using the H-cube®'s 10% Pd/C catalyst and hydrogen gas Background: The palladium catalyzed reduction of alkenes, using a 10% Pd on carbon catalyst and hydrogen gas, is an important reaction for hydrogenating double bonds. A large number ofreactions performed in industry, from the search for new pharmaceutical compounds to advanced material synthesis, are catalyzed reductions, and there is a paucity of such reactions in the undergraduate organic laboratory curriculum due to safety concerns with the handling of hydrogen gas in sizable quantities. While there are recent reports of the use of ammonium formate to generate hydrogen gas in situ for PdC catalyzed reductions of chalcones, this laboratory experiment e Thales Nano TME as a demonstration of the convenience, safety, and ease H-cube makes u of of use of a continuous flow reaction system. Curcumin is the primary curcuminoid component of the well-known spice from India, turmeric. While curcumin can be extracted from turmeric in large quantities, other curcuminoids will be present, such as the desmethoxycurcumin (3) and the bis-desmethoxycurcumin (4). Curcumin has been used in Indian medicine since 1900 BC, and it has recently been demonstrated to have several medicinally relevant activities, such as anti-inflammatory, anti-carcinogenic, and anti- viral. While curcumin is suspected to be largely responsible for the useful bioactivity of turmeric, analogs of curcumin such as the tetrahydro-curcumin are also of medicinal interest. HO OH HO OH An interesting characteristic of curcumin (1) is it's bright, canary-yellow color. Hydrogenation of curcumin (1) to tetrahydro-curcumin (2) destroys the conjugation, though keto-enol tautomerism is still present. OH O HOT OH HO OH 1 (Keto-Form) 1 (Enol Form

Explanation / Answer

The extended conjugation shifts absorption wavelength to higher values pushing it into the visible region and hence imparting bright colous to compounds. In case of beta carotene, there are several double bonds in conjugation and pi-pi* transition is responsible for its colour. In case of circumin, n-pi* transition is the active chromophore and the extension in conjugation shifts absorption to visible wavelength. The enol form has more continuity in conjugation than the keto form.

After reduction, though keto-enol tautomerism is still present , the extended conjugation is lost and so, the n-pi* transition does not produce strong colour.

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