Education
A solid understanding of NMR spectroscopy is a basic learning goal for any student of chemistry. The hands-on approach to learning is the most powerful method for instructors in both classroom settings and in the teaching laboratory. Direct experience with acquiring and processing NMR spectra to determine product purity or to monitor the course of a chemical reaction is extremely valuable, especially for organic chemistry students.
The challenges for teaching lab directors and instructors of organic chemistry in applying modern NMR techniques are manifold:
- Accessing modern high-field research NMR facilities for student instruction.
- Managing complex and technically challenging instrumental operations.
- Funding expensive equipment dedicated solely to teaching.
- Housing oversized instrumentation in existing lab space.
- Developing NMR applications to complement existing lab curricula.
- Allowing undergraduate chemistry students direct access to an expensive instrument.
- Gaining or maintaining American Chemical Society (ACS) or other national accreditation by incorporating NMR into the curriculum.
The picoSpin-45 1H NMR spectrometer offers solutions to these challenges.
- Designed to be compact and lightweight, without requirements for liquid cryogens or other special facilities, the picoSpin-45 spectrometer can easily fit on existing laboratory bench tops and can easily be relocated as needs change.
- With its small footprint, it is conveniently stored when not in use.
- Its capillary design, easy-to-shim permanent magnet and simple software interface dispense with complicated initialization and operation procedures.
- Chemistry students can acquire their own spectra in the lab without having to wait for TAs or other staff to run their samples.
- Instructors can focus on NMR applications without having to worry about many of the technical aspects of instrument operation, making the picoSpin-45 ideal for all levels of the chemistry curriculum – for majors and non-majors alike. Low purchase and operational costs make the picoSpin spectrometer far more affordable than traditional NMR instrumentation.
- The picoSpin-45 spectrometer is ideal for routine identification of reaction mixtures and crude or purified products at the lab bench.
- Lab procedures are easily adapted to take advantage of both qualitative and quantitative techniques.
Figure 1. picoSpin-45 NMR Spectrum of Ethylacetate (neat, 4 scans):
The 1H NMR spectrum of ethyl acetate shows three individual signals due to three different hydrogen environments. The protons of the keto-methyl group (H3CC=O) appear up field with a chemical shift value of 2.04 ppm. These protons experience no spin-spin coupling, and thus appear as a single peak with a weight of 3. Protons of the ethyl group experience two different chemical environments. Methylene protons (-CH2-) attached to the more electronegative oxygen are deshielded and shifted down field to 4.12 ppm with a peak integral of 2. The methyl protons (-CH3) of the ethyl moiety are the most shielded and appear farthest up field at 1.26 ppm with a peak integral of 3.
Asymmetry in the ethyl group results in vicinal coupling of the terminal methyl (-CH3) protons to the methylene (-CH2-) protons, yielding a simple first-order splitting pattern with expected multiplicities of a triplet and quartet. The -CH2- proton signal is split into a quartet (δ4.12) by the three neighboring methyl protons, and the –CH3 proton signal is split into a triplet (δ1.26) due to the two adjunct methylene protons. This splitting pattern is unmistakable and easily resolved by the picoSpin-45 spectrometer.
The small signal at 2.75 ppm indicates the presence of water as an impurity in the sample.
The Aldol Condensation Reaction
