Introduction

Table of Contents

Changes, corrections, and updates to the textbook content.

Who is this textbook intended for?

When writing this textbook, our goal was to demonstrate how to use NMR spectroscopy to determine or confirm the structure of small- to medium-sized organic molecules. The reader will not find, for example, information on NMR spectroscopy applications for studying protein structures or other macromolecules – those topics are covered in specialized publications. Our primary audience is chemists working in organic synthesis and the study of the physicochemical properties of organic compounds. In their research, verifying the molecular structure of synthesized compounds is a routine task. Sometimes, the synthesis product differs from expectations, and determining its structure becomes necessary. This also applies to chemists studying organic compounds isolated from living organisms. Furthermore, this textbook will benefit advanced chemistry students and Ph.D. candidates conducting research in the broadly understood field of organic chemistry. We also hope that NMR laboratory staff will find it useful, perhaps discovering inspiring examples of unusual applications of NMR techniques to solve specific problems.

It is important to note that this textbook is not an introduction to the basics of NMR. Individuals seeking to understand the theoretical foundations of this technique and the measurement methods offered by modern NMR are encouraged to consult the textbook „Nuclear Magnetic Resonance Spectroscopy – Basics and Measurement Methods,” authored by Prof. Jarosław Jaźwiński, available on the website of the Institute of Organic Chemistry of the Polish Academy of Sciences. In this work, we approach NMR spectroscopy from the perspective of chemists interested in obtaining as much information as possible about the molecular structure of the compounds under investigation.

What is included in the textbook?

The textbook consists of six chapters. Chapter 1, which serves as an introduction, briefly covers the following topics:

Programs for independent processing of NMR spectra,
NMR spectrum libraries available on the Internet,
Estimating chemical shifts in ¹H and ¹³C NMR spectra based on substituent increments,
NMR spectrum simulation,
Molecular modeling and calculation of coupling constants using the Karplus equation and its modifications,
Calculation of chemical shifts and coupling constants using quantum chemistry methods.

More detailed information on these topics will be found in subsequent chapters, where we thoroughly describe how to use various NMR measurement techniques and computational methods to determine molecular structures of organic compounds.

Chapter 2, titled „Fundamentals of NMR Spectrum Interpretation,” outlines methods of NMR spectrum interpretation, ranging from the simplest to more advanced approaches. This chapter is divided into two parts: the first deals with spectra of aliphatic compounds, both chain and cyclic, and the second with aromatic compounds. The chapter begins with examples of compounds where one-dimensional spectra, supported by predicted chemical shifts using the appropriate computer programs described in Chapter 1, are sufficient for assigning chemical shift values to individual carbon and hydrogen atoms. In later sections, we describe more complex molecules that require two-dimensional spectra. The chapter concludes with exercises and original files generated by the spectrometer during measurements (i.e., FID files with auxiliary files). More information on the structure of individual chapters is provided below.

Chapter 3, „Application of NMR Spectroscopy to Solve Stereochemical Problems,” is, in our opinion, one of the most important parts of the textbook. It provides a detailed description of various measurement techniques and methods for interpreting NMR spectra to obtain comprehensive information about the spatial structure of the studied molecule. We also show how to use appropriate computer programs to aid, or even enable, spectrum interpretation and its correlation with molecular structure. This chapter also includes exercises of varying difficulty.

Chapter 4, „Dynamic Effects in NMR Spectra,” addresses three groups of topics. The first concerns amide spectra, where hindered rotation around the bond between the carbonyl group and the amide nitrogen atom is observed. The second group involves the influence of hindered rotation or ring inversion caused by steric hindrance on the spectrum’s appearance. We demonstrate the importance of solvent choice and measurement temperature. The third section discusses compounds in which equilibrium between tautomers is established in solution, as well as compounds that exist as a single isomer in the solid state but partially convert to another isomer upon dissolution.

Chapter 5 provides a concise overview of NMR spectra of nuclei other than carbon and hydrogen, as well as the effects of these nuclei on proton and carbon spectra. We focus primarily on spectra of compounds containing nitrogen, fluorine, and phosphorus, but also show examples of spectra from other nuclei.

Chapter 6 covers the interpretation of spectra from more complex organic compounds, particularly those with practical applications in organic synthesis, natural compounds of significant importance, or biologically active compounds used as drugs. This chapter will be continuously supplemented with new examples. If readers wish to share examples of interesting spectra, we encourage them to submit these to us, along with the original FID files. Please remember that, upon publication, these spectra will be available to everyone under a Creative Commons BY-NC license (see below).

How to use this textbook?

To effectively analyze NMR spectra of complex molecules, it is necessary to have high-resolution prints. By „prints,” we also mean PDF files viewable on a screen, which are entirely sufficient for reading through the chapters. However, when interpreting NMR spectra of a new compound, it is helpful to have printed copies of the spectra, allowing one to annotate, for example, couplings between signal groups and mark other important information. The text of this work can be read directly on a monitor or even a tablet, but it is also advisable to have the option to print it and use it like a traditional book. Therefore, Chapters 2–6 have been prepared in the following formats:

HTML file with a table of contents and links to other files.
PDF file containing the main text of the chapter, with thumbnails of most figures. This file begins with an interactive table of contents leading to individual subsections and can be downloaded for offline use, as can the other PDF files.
PDF file with all the illustrations from the main text in full resolution, numbered in order of appearance.
Problems texts (PDF).
PDF file containing spectra necessary for solving the problems.
PDF file with hints for solving problems.
Solutions to problems (PDF).
HTML list of spectra used in the chapter, with links to their prints and compressed original FID files with auxiliary files.

Thus, while reading the main text, it is recommended to have the illustration file open in a separate window, ideally on a second monitor. Of course, selected files can also be printed. Chapters 2 and 3 include tasks and problems for independent resolution. For those who find a task too difficult but do not wish to immediately consult the solution, we have included a separate file with hints on how to approach solving the task, which should facilitate its completion.

A crucial element of this textbook is the collection of all spectra used in the chapters. These are the original files generated by the spectrometer during measurements (i.e., FID files with auxiliary files) and ready-to-print versions. Among these are spectra that are indicated in the text as available in supplementary materials.

FID files are intended for practicing the independent processing of NMR spectra using commercial or free software available on the Internet—more information on this can be found in Chapter 1. The list of these files (separate for each chapter) is alphabetically organized by compound names or symbols. Each entry includes two links: one to a ZIP file containing all the spectra recorded for that compound, and the second to ready-to-print spectra.

Changes, corrections, and updates to the textbook content

The creation of this textbook is a gradual process, which is why we decided to create a website and post the parts that are ready for publication. As described above, Chapter 6 will be continually updated with new examples. On the homepage of the textbook’s website, there is a link to the „What’s New?” page, where we will provide updates on any changes and additions to the content.

As planned, this textbook is intended to be „living,” meaning that more examples of NMR spectra will be successively added to illustrate important issues encountered in interpretation. We also encourage readers to submit their spectra if they wish to share them with the community. Please remember that, upon publication, these spectra will be available to everyone under the Creative Commons BY-NC license (see below).

Copyright information

The copyright of this textbook is held by the Institute of Organic Chemistry of the Polish Academy of Sciences in Warsaw. All materials are published under a Creative Commons license with attribution and non-commercial use (CC BY-NC). This means that they can be used, for example, to create lectures, presentations, databases, etc., provided their source is acknowledged with the following text:

in a clearly visible form. Works created using these materials cannot be distributed commercially.

Contact the authors

For any questions related to the use of the textbook or to report errors, please contact: witold.danikiewicz@icho.edu.pl or olga.staszewska@icho.edu.pl.