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15.14 Spectroscoic Analysis of Alcohols and Thiols:

Dive into the characteristic spectroscopic features of alcohols and thiols using Infrared (IR) and Nuclear Magnetic Resonance (NMR) techniques. Explore O–H and C–O stretching absorptions, chemical shifts in NMR spectra, and more.

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15.14 Spectroscoic Analysis of Alcohols and Thiols:

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  1. 15.14 Spectroscoic Analysis of Alcohols and Thiols: Infrared (IR): Characteristic O–H stretching absorption at 3300 to 3600 cm1 Sharp absorption near 3600 cm-1 except if H-bonded: then broad absorption 3300 to 3400 cm1 range Strong C–O stretching absorption near 1050 cm1 % T O-H C-O cm-1

  2. 1H NMR: protons attached to the carbon bearing the hydroxyl group are deshielded by the electron-withdrawing nature of the oxygen,  3.3 to 4.7 = 0.9, d, 3H = 1.5, q, 2H = 1.7, m, 1H = 3.65, t, 2H = 2.25, br s, 1H 22.6 61.2 41.7 24.7 CDCl3 O-H C-O

  3. Usually no spin-spin coupling between the O–H proton and neighboring protons on carbon due to exchange reaction The chemical shift of the -OH proton occurs over a large range (2.0 - 5.5 ppm). It chemical shift is dependent upon the sample concentration and temperature. This proton is often observed as a broad singlet (br s). Exchangable protons are often not to be observed at all.

  4. 13C NMR: The oxygen of an alcohol will deshield the carbon it is attached to. The chemical shift range is 50-80 ppm  14  19  35  62 CH3 —CH2 —CH2 —CH2 —OH DMSO-d6 (solvent)

  5. 15.48 (fig 15.8, p. 658) 13C: 138.6 129.4 128.4 126.3 68.8 45.8 22.7 13C: 145.2 128.8 127.8 126.5 76.3 32.3 10.6

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