NMR Spectrum of Butanol

Butanol, C₄H₉OH, is a high value C4 alcohol collectively represented by four isomeric structures: 1-butanol, 2-butanol, isobutanol and tert-butanol. Isomers are compounds that have the same molecular formula but which the connectivity of the atoms differ.

In chemistry education, butanol offers an easily accessible series of isomers for studying the effect of structure on reaction mechanism, synthesis, chemical properties, thermodynamics and spectroscopy. Isomers of butanol also offer a diverse mix of industrial and commercial applications. In general, butanol is used as solvents in paints, resins, fats and waxes and in industrial coatings, as raw materials and chemical intermediates in the production of safety glass, hydraulic fluids, plastics and rubber. It has use as a cleaner and in floor polishers; it is used in the production of cosmetics, such as lipstick and foundation, and as an extraction solvent in the production of drugs, hormones and antibiotics.

The linear chain 1-butanol is a primary alcohol that has high commercial value as a transport fuel, similar to ethanol, and can be used in the production alternative gasoline fuel blends and jet fuels. Butanol is produced conventionally from petrochemical stock. Increasingly, however, biomass conversion processes akin to ethanol fermentation of high-energy renewable feedstocks is being applied to the production of butanol. This biobutanol is a compatible ‘drop-in’ fuel alternative to ethanol that can be used with existing car engines.

Spectra of the isomers of butanol obtained using the Thermo Scientific picoSpin 45 spectrometer are distinct. This series of spectra compiles the experimental 1H NMR spectra of the four regioisomers of butanol. From bottom up, the spectra are of 1-butanol in CHCl₃, 2-butanol in acetone, isobutanol in acetone and tert-butanol in CHCl₃. The positional isomers 1-butanol and 2-butanol differ from the constitutional isomers isobutanol and tert-butanol in their carbon backbone connectivity.

The NMR spectrum of these isomers is distinct due to these changes in connectivity, which in turn affects the local molecular symmetry and splitting patterns arising from differences in the number of ¹H-¹H couplings. As the OH functional is repositioned along the carbon backbone, it influences both multiplicity and the chemical shift position of adjacent protons, often resulting in improved spectral clarity. With NMR, these structural changes are easily observed in the ¹H spectrum.

The picoSpin 45 ¹H NMR spectrometer has a wide range of utility in chemical education. Bench top NMR in the teaching lab can be used as an analytical tool to explore concepts in NMR and chemical structure. It also has utility to investigate and extract dynamic information, such as during chemical synthesis, and can be used for routine analysis and testing of reactions, extractions, or separations.

NMR Lesson Plan: Regioisomers of Butanol

Chemical name: Butanol (1-butanol, 2-butanol, isobutanol and tert-butanol)
Experimental conditions: 10 scans
Concentration: 50% (v / v) in CHCl3 or acetone
CAS No: 71-36-3 (1-butanol), 78-92-2 (2-butanol), 78-83-1 (isobutanol), 75-65-0 (tert-butanol)
Field: 45MHz
Nuclear testing: 1H
Applications: Chemical education, structure characterization

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