Using Nuclear Magnetic Resonance Spectroscopy to Deduce Structure

Using Nuclear Magnetic Resonance Spectroscopy to Deduce Structure 

In this chapter we address the question that faces anyone trying to identify the molecular structure of a substance, namely, What is it To put it another way, this chapter begins to answer the obvious question that you may already have been thinking after the first nine chapters of this book, namely, How does anyone really know that all those molecules are what we say they are In the olden days, tedious indirect identification methods had to be used, and some are described in the text. Nowadays these questions are answered through the use of spectroscopy, a technique that serves as the eyes of an organic chemist with respect to the structures of molecules. The most important and widely used type of spectroscopy, nuclear magnetic resonance (NMR), is described in this chapter. 

The classical (translate as tedious ) methods of structure elucidation. 

An example of fairly simple physics put to very good use. A general overview of NMR spectroscopy. 

The first two pieces of information available from an NMR spectrum. 

We have seen that one of the main goals of studying organic chemistry is to appreciate how details of molecular structure affect the ways in which molecules function in reactions— whether those reactions take place in industrial settings, in laboratory syntheses, or within the body. But how do we know the detailed struc-tnres of molecules How can we identify new products or be sure that we have isolated the product we want from a reaction mixture  

Wouldn t it be nice if we had some technique that could allow us to recognize the presence of certain nuclei in a molecule, count their relative numbers, describe the nature of their electronic enviromnent, and tell us how they are connected to other atoms  

We begin with a brief consideration of how classical physical measurements and chemical tests can help in determining a compound s structure. Then we shall discuss how spectroscopy works, how we can interpret its results, and what information we can obtain from the latest advances in spectroscopic instruments and techniques. 

A researcher prepares to insert a sample into the probe of one of the most powerful NMR spectrometers in the world. 

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Chapter 10 USING NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY TO DEDUCE STRUCTURE... 

I7H 10 Use of Nuclear Magnetic Resonance Spectroscopy to Deduce Structure... 

MRI is based on nuclear magnetic resonance (NMR) spectroscopy which is widely used to deduce the structures of organic molecules. Given the public perception of the word nuclear (nuclear bombs, nuclear waste, etc) this has been dropped from the acronym used for the technique. In NMR spectroscopy a sample... 

Virtually, all students of chemistry, biochemistry, pharmacy and related subjects learn how to deduce molecular structures from nuclear magnetic resonance (NMR) spectra. Undergraduate examinations routinely set problems using NMR spectra, and masters and doctoral theses describing novel synthetic or natural products provide many examples of how powerful NMR has become in structure elucidation. Existing texts on NMR spectroscopy generally deal with the physical background of the newer and older techniques as well as the relationships between NMR parameters and chemical structures. Very few, however, convey the know-how of structure... 

The 20th century saw the development and spread of a battery of powerful physical methods used to discover the structures of organic compounds. These methods include ultraviolet, infrared, and nuclear magnetic resonance (nmr) spectroscopy as well as mass spectrometry and Z-ray crystallography. So formidable is this array that, in many cases, the time needed to deduce a structure now occupies minutes rather than months. Techniques that, for the first century of organic chemistry, had been standards of structure assignment became superfluous. They included the investigation of the... 

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