Abstract

This laboratory experiment teaches students how to use a Thermo Scientific™ picoSpin™ 45 NMR spectrometer and interpret experimentally-acquired 1H NMR spectra. In this lab, students obtain the 1H NMR spectrum of an unknown organic liquid chosen from a variety of compounds representing multiple functional groups. This can be followed by student presentations of experimental results and spectral interpretation. This lab can be easily meshed with other experiments to engage students in instrumental measurements during the entire lab period.

Miami University of Ohio Spectra Data

Pre-lab preparation

1. Make sure you have read and reviewed the posted NMR lecture notes and Chapter 16 of the Klein (1st edition) text.
2. For each of the unknown compounds listed below, draw the chemical structure in your lab notebook and label all functional groups. Also determine the IHD (index of hydrogen deficiency) for each compound.
3. Instructions for using the picoSpin 45 NMR spectrometer will be provided in lab.

Experimental results and class presentation

Students will work in pairs and run the 1H NMR spectrum of an unknown organic compound chosen from those listed below. All of the compounds are liquids and the unknown samples will be spiked with TMS (tetramethylsilane) at approximately 10% (v/v). The TMS signal should be easily observed and will be used to normalize the spectrum of your unknown.

The spectra will be acquired during the first week of this lab. For the following week, each pair of students will present their experimental results and identification of their unknown to the class, including a complete analysis of the 1H NMR spectrum. Bring a flash drive to lab so you can obtain an electronic copy of the spectrum of your unknown to use in the presentation.

Possible Unknowns

Ethyl acetate   2-butanone
Ethyl benzene 4-methoxybenzaldehyde
Methyl salicylate 2-furaldehyde
1-chloropropane 1-chloro-2-methylpropane
trans-cinnamaldehyde Propanoic acid

In the class presentation, include the structure of the compound either neatly drawn by hand or using ChemDraw (chemical structure drawing software loaded on the iPads that are available for student use from the library). On your drawing, show all hydrogen atoms and label each unique set A, B, C, etc. For the interpretation of your 1H NMR spectrum, assign each observed signal using these labels. Discuss the number of signals, the chemical shift values, integration of the signals, and splitting (multiplicity), including coupling constants (J values) if observed and interpretable.

Turn in a copy of your 1H NMR spectrum with the unknown code indicated along with your pre-lab notebook pages. Also prepare a table for the interpretation of your spectrum and identification of your unknown. You do not need to write an experimental procedure, observations, or conclusion in your lab notebook. The class presentation, the labeled structure of your compound, and the table showing the interpretation of your spectrum will suffice.

About the authors

Dr. Janet Marshall is a lecturer in the Department of Chemistry & Biochemistry at Miami University of Ohio – Middletown campus. She received her B.S. in Chemistry from the University of North Carolina at Chapel Hill and completed her Ph.D. in Chemistry at the California Institute of Technology.

Mr. Howard Vail is a lecturer in the Department of Chemistry & Biochemistry at Miami University of Ohio – Middletown campus. He received his B.S. and M.S. in Chemistry from Western Kentucky University.

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