Deciphering the Atom

Morris, Richard. The last sorcerers the path from alchemy to the periodic table. Washington (DC) Joseph Henry P, 2003. xii, 282 p. ISBN 0-309-08905-0 Contents Preface — 1. The four elements — 2. Prelude to the birth of chemistry — 3. The sceptical chymist — 4. The discovery of the elements — 5. A nail for the coffin — 6. "Only an instant to cut off that head" — 7. The atom — 8. Problems with atoms — 9. The periodic law — 10. Deciphering the atom — Epilogue the continuing search — appendix. A catalog of the elements — Further reading — Index... 

FIGURE 2.28 An aid to deciphering the constitution of coupling reagents from their abbreviations. HBPyU and HAPyU correspond to incorrect names of the compounds because U = uronium = OC+N2 includes the nitrogen atoms of the pyrrolidine rings. The substitutents on each nitrogen are tetramethylene. 

Currently, there are no accurate methods available for quantifying the aliphatic bridges in the coal macromolecule. Quantitative nature of the application of infrared (IR) spectroscopy is limited to certain general types of functional groups or bond types. Nuclear magnetic resonance spectroscopy, despite the success of dipolar dephasing techniques to decipher the extent of substitution on carbon atoms, is still inadequate to distinguish distinct structural entities . 

Clearly, atoms were not the indivisible things they were always thought to be. Chemistry had made great steps toward deciphering the key to the universe, but there was much more to be learned. If physicists were to learn what the universe was made of, it would be necessary to understand atomic structure. 

Peeking inside the atom Protons, eiectrons, and neutrons Deciphering atomic numbers and mass numbers Understanding isotopes and caicuiating atomic masses... 

A fundamental component of the interpretation of NMR data is deciphering the NMR assignments, which correlates an observable NMR resonance with a specific atom in the molecular structure of the metabolite. This process is illustrated using the structure and H NMR spectrum of 1,3-dimethylnaphtha-lene as an example (Fig. 12.6). The two methyl groups have distinct H NMR chemical shifts because of their unique local environments. The NMR assignment process results in attributing the NMR peak at 2.57 ppm to methyl (a) and NMR peak 2.39 ppm to methyl (b). 

Finally, we note that Figure 17.2 and the above brief discussion of acetylene photodissociation (Section 17.1) serve to illustrate the increasing complexity of PESs, which are already quite challenging even for molecules containing only four atoms. We shall discuss other possible ways of deciphering the complex dynamics involved in the photodissociation of large polyatomic molecules at the end of Chapter 19, and some further examples of polyatomic photodissociation dynamics will be discussed in Chapter 18, which is concerned with multiphoton excitation. 

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