Deuterium

Discovery and Applications in Organic Chemistry

Jaemoon Yang

• Publisher: Elsevier
• Year: 2016
• Print ISBN: 9780128110409
• eBook ISBN: 9780128110416
• Topic: Physical Sciences
• Subtopic: Biochemistry

Deuterium: Discovery and Applications in Organic Chemistry provides a well-illustrated overview of the discovery of 2H or heavy hydrogen, the stable hydrogen isotope with both a proton and a neutron in its nucleus. The work introduces the isotope, its discovery, physical properties, nomenclature, and common compounds, also exploring its application in organic chemistry through classic and recent examples from literature. Finally, the book devotes one chapter to Deuterium in medicinal chemistry and the biological effects of Deuterium Oxide, better known as D2O. - Provides unique coverage not found elsewhere that is presented in an accessible, dedicated short work - Contains practical information and examples on the use of Deuterium (D or 2H, Heavy Hydrogen) in organic synthesis - Presents a detailed description of Deuterium's discovery and applications in the pharmaceutical industry

Chapter 1

Isotopes

Abstract

Isotopes are a group of chemical elements that have the same number of protons, but have a different number of neutrons. Isotopes thus have a different atomic mass, but maintain the same chemical characteristics. It was Frederick Soddy, who first proposed the word “isotopes” in 1913. The hydrogen atom is the simplest of all atoms: it consists of a single proton and a single electron. In addition to the most common form of the hydrogen atom that is called protium, two other isotopes of hydrogen exist: deuterium and tritium. The atoms of deuterium (atomic symbol: D or ²H) contain one proton, one electron, and one neutron, while those of tritium (atomic symbol: T or ³H) contain one proton, one electron, and two neutrons. Organic molecules that contain carbon–hydrogen bonds constantly undergo myriad reactions. Organic chemists use deuterium to investigate reaction mechanism.

Keywords

Isotopes; Frederick Soddy; protium; deuterium; organic chemists; reaction mechanism

Outline

1.1 Definition

1.2 Isotopes of Hydrogen

1.3 Uses of Deuterium in Organic Chemistry

References

1.1 Definition

Isotopes are a group of chemical elements that have the same number of protons, but have a different number of neutrons.¹ Isotopes thus have a different atomic mass, but maintain the same chemical characteristics. Nearly all the chemical elements that make up our material world occur in different isotopic forms. In fact, 83 of the most abundant elements have one or more isotopes composed of atoms with different atomic masses. Some familiar examples are chlorine (Cl), bromine (Br), carbon (C), and oxygen (O): chlorine has two stable isotopes of masses of 35 and 37; bromine has two isotopes of masses of 79 and 81; carbon has two stable isotopes of masses of 12 and 13; and oxygen has three stable isotopes of masses of 16, 17, and 18.

It was Frederick Soddy, who first proposed the word “isotopes” in 1913 in a paper published in Nature.²

So far as I personally am concerned, this has resulted in a great clarification of my ideas, and it may be helpful to others, though no doubt there is little originality in it. The same algebraic sum of the positive and negative charges in the nucleus, when the arithmetical sum is different, gives what I call “isotopes” or “isotopic elements,” because they occupy the same place in the periodic table. They are chemically identical and save only as regards the relatively few physical properties, which depend upon atomic mass directly.

Reprinted with permission from Macmillan Publishers Ltd: Soddy, F. Nature, 1913, 92, 399. Copyright 1913.

Soddy received the 1921 Nobel Prize in chemistry for his contributions to our knowledge of the chemistry of radioactive substances and his investigations into the origin and nature of isotopes:³

Soddy was born in Eastbourne, England, on September 2, 1877. He studied at Eastbourne College and the University College of Wales, Aberystwyth. In 1895, he obtained a scholarship at Merton College, Oxford, from which he graduated in 1898 with first class honors in chemistry. After 2 years of research at Oxford, he became a demonstrator in chemistry at McGill University in Montreal. At McGill, he worked on radioactivity with British physicist Sir Ernest Rutherford. Together they published a series of papers on radioactivity and concluded that it was a phenomenon involving atomic disintegration with the formation of new kinds of matter. In 1903, Soddy left Canada to work at University College London with Scottish chemist Sir William Ramsay. From 1904 to 1914, Soddy served as a lecturer at the University of Glasgow, Scotland. During this period, he evolved the so-called “Displacement Law,” namely that emission of an alpha particle from an element causes that element to move back two places in the Periodic Table. In 1908, he married Winifred Beilby. The couple had no children. In 1919, he became Lee’s Professor of Chemistry at Oxford University, a position he held until 1937 when he retired on the death of his wife. He died in Brighton, England, on September 22, 1956, at the age of 79.

1.2 Isotopes of Hydrogen

The hydrogen atom is the simplest of all atoms: it consists of a single proton and a single electron. In addition to the most common form of the hydrogen atom that is called protium, two other isotopes of hydrogen exist: deuterium and tritium. The atoms of deuterium (atomic symbol: D or ²H) contain one proton, one electron, and one neutron, while those of tritium (atomic symbol: T or ³H) contain one proton, one electron, and two neutrons. Whereas protium and deuterium are stable, tritium is not: it is radioactive. It is interesting to note that only the hydrogen isotopes have different names.

1.3 Uses of Deuterium in Organic Chemistry

Organic molecules that contain carbon–hydrogen bonds constantly undergo myriad reactions, in which reactants become products after going through a certain pathway. Organic chemists are very curious about the mechanism of the reaction, as a thorough understanding of the reaction mechanism not only provides the details of chemical change but also forms the foundation for invention of new reactions. Thus the elucidation of reaction mechanism is a rewarding process.

Among the many ways of studying reaction mechanism available to organic chemists, the use of deuterium is a very powerful tool especially when the reaction involves hydrogen.⁴

There are two properties that make deuterium so useful in organic chemistry. First, it is twice as heavy as protium (Table 1.1). When the hydrogen is replaced by deuterium, the resulting deuterium-labeled compound can be readily distinguished from the ordinary compound by mass spectra. Another advantage is taken of the heavy weight of deuterium in the study of deuterium kinetic isotope effect (DKIE). As the C–H bond breaks faster than the C–D bond, the measurement of the relative reaction rate gives a good idea about the reaction mechanism if that bond is involved in the reaction being investigated.

Table 1.1

Some Properties of Protium and Deuterium

Atom	H, protium	D, deuterium
Natural abundance	99.985%	0.015%
Atomic mass	1.008	2.014
Nuclear spin	1/2	1

Second, deuterium has different magnetic properties than protium. Thus the C–H bonds of an organic compound can be detected by ¹H NMR, whereas the C–D bonds cannot.⁵ The opposite is true with ²H NMR spectroscopy. This unique feature makes it possible to follow deuterium attached to a specific carbon during the reaction. The combination of mass spectra with NMR spectroscopy thus makes it possible to employ deuterium as an isotopic tracer in an endeavor to solve the mechanism puzzle.

Deuterium is a rare isotope of hydrogen: there exists only one deuterium to about 6500 protiums found in nature. It is therefore no surprise that deuterium had only been discovered about 80 years ago. In the next chapter, we will learn how deuterium was discovered.

References

1. Krebs RE. The history and use of our Earth’s chemical elements Greenwood Press 1998;27–28.

2. Soddy F. Nature. 1913;92:399.

3. NobelPrize.org. Frederick Soddy—biographical. Chem Eng News. 2013;December 2:30–31.

4. Semenow DA, Roberts JD. J Chem Educ. 1956;33:2.

5. Smith ICP, Mantsch HH. Deuterium NMR spectroscopy, vol. 191. ACS Symposium Series; 1982; pp. 97–117 [Chapter 6].

Chapter 2

Deuterium

Abstract

Deuterium was discovered by Harold C....

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• Acknowledgments
• Introduction
• Chapter 1. Isotopes
• Chapter 2. Deuterium
• Chapter 3. Deuterium-Labeled Compounds
• Chapter 4. Applications in Organic Chemistry
• Chapter 5. Applications in Medicinal Chemistry
• Conclusion
• Author Index