Ketones

¹HNMR

In ¹H NMR spectroscopy, ketones exhibit characteristic proton signals influenced by the electron-withdrawing effect of the carbonyl group (C=O). Protons on carbons adjacent to the carbonyl (α-protons) are deshielded and typically appear in the range of 2.1–2.6 ppm, while protons on carbons further removed (β-protons and beyond) resonate upfield, usually between 1.0–1.8 ppm, depending on their distance from the carbonyl. For example, in 3-pentanone, the symmetry of the molecule results in a simple spectrum: the methylene protons (CH₂) adjacent to the carbonyl appear as a quartet near 2.4 ppm, coupled to the terminal methyl protons (CH₃), which appear as a triplet around 1.0 ppm.

¹³CNMR

In ¹³C NMR spectroscopy, the carbonyl carbon of ketones is highly deshielded and appears prominently in the range of 190–220 ppm. The α-carbons typically resonate near 30–50 ppm, while β-carbons and beyond appear further upfield, around 10–30 ppm. In 3-pentanone, the carbonyl carbon appears near 210 ppm, the α-methylene carbons around 40 ppm, and the terminal methyl carbons near 10 ppm. The simplicity of 3-pentanone's ¹H and ¹³C NMR spectra, due to its symmetry, makes it an excellent example for understanding the NMR features of ketones. Below are the ¹H NMR and ¹³C NMR spectra for 3-pentanone, illustrating these trends.