1) What is the purpose of the concentrated sulfuric acid in Pinacol rearrangemen
ID: 765384 • Letter: 1
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1) What is the purpose of the concentrated sulfuric acid in Pinacol rearrangement? (Pinacol to Pinacolone) 2) Discuss how infrared spectroscopy (IR) can be used to distinguish between pinacol and pinacolone.Explanation / Answer
1) Conc. H2SO4 is responsible for the protonation of one of the -OH groups 2)Infrared spectroscopy (IR spectroscopy) is the spectroscopy that deals with the infrared region of the electromagnetic spectrum, that is light with a longer wavelength and lower frequency than visible light. It covers a range of techniques, mostly based on absorption spectroscopy. As with all spectroscopic techniques, it can be used to identify and study chemicals. A common laboratory instrument that uses this technique is a Fourier transform infrared (FTIR) spectrometer. 3) The pinacol to pinacolone rearrangement is... OH OH CH3 O | | | || CH3 — C — C — CH3 —— H2SO4 ——> CH3 — C — C — CH3 + H2O | | | CH3 CH3 CH3 Pinacol and pinacolone would be easily distinguished in IR. Pinacol would have a broad strong absorption around 3000 - 3400 cm?¹ characteristic of O — H bond stretches. This would be absent in pinacolone. Pinacolone would have a very intense absorption peak between 1650 and 1800 cm?¹ for the C = O bond stretch, which would be absent in the IR spectrum of pinacol. In addition, there would be absorptions corresponding to the C — O bond stretches near 1200 cm?¹ in the pinacol spectrum that would not be observed in the pinacolone IR spectrum. NOTE: The presence of water in the pinacolone product would lead to a broad O — H bond stretch being observed in the spectrum... this impurity could be distinguished from unreacted pinacol either by comparison to the pinacol spectrum, or by checking for the presence or absence of C — O bond stretches. As in any synthesis work, care should be taken to ensure the product was dry and pure before collecting spectral data.
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