Alcohols

¹HNMR

In ¹HNMR spectroscopy, the chemical shifts of protons in alcohols are influenced by the electronegativity of the oxygen atom, which deshields nearby protons. The hydroxyl proton (OH) itself typically appears as a broad singlet, often ranging from 0.5 to 5.0 ppm, depending on the extent of hydrogen bonding, solvent effects, and concentration. This signal can sometimes exchange with deuterium in deuterated solvents like D₂O, causing it to disappear.

Protons on the carbon adjacent to the hydroxyl group (α-protons) are deshielded due to the electron-withdrawing effect of the oxygen, typically appearing in the range of 3.3–4.0 ppm. Protons on carbons further removed from the hydroxyl group (β-protons and beyond) experience less deshielding and generally resonate in the range of 1.0–1.7 ppm, similar to alkanes, though slightly downfield due to the inductive effect of the oxygen. The exact chemical shifts can vary depending on the alcohol's structure and the solvent used. Below are the ¹H NMR and ¹³C NMR spectra for 2-butanol, illustrating these features.

¹³CNMR

In ¹³C NMR spectroscopy, the carbon atoms in alcohols are influenced by the electronegativity of the oxygen atom, which deshields the carbons to which it is directly bonded. The carbon bearing the hydroxyl group (the α-carbon) typically appears in the range of 50–80 ppm, significantly downfield compared to typical aliphatic carbons due to the electron-withdrawing effect of the oxygen. Carbons adjacent to the α-carbon (β-carbons) are also deshielded, though to a lesser extent, and usually resonate in the range of 20–40 ppm. Carbons further removed from the hydroxyl group (γ-carbons and beyond) exhibit chemical shifts closer to those of alkanes, typically falling within 10–30 ppm. The exact chemical shifts can vary depending on the alcohol's structure, solvent, and concentration. Below is the ¹³C NMR spectra for 2-butanol, illustrating these trends.