Hydrogen Attached to Elements Other than Carbon

The predicted chemical shift of these aromatic hydrogens is 5 7.27 + 0.58 + 0.21 = 8.06. Note the close similarity of its spectrum to the one described in Example 6.17.  

6 HYDROGEN ATTACHED TO ELEMENTS OTHER THAN CARBON 

With more than 100 elements besides carbon in the periodic table (Appendix 2), you might fear that the number of H chemical shift correlations is endless. However, except for a few specialized applications, the most important heteroatoms to which hydrogen finds itself bonded are oxygen and nitrogen. But before we discuss these two specific cases, here is a useful generalization As the electronegativity (Table 6.1) of X increases, both the acidity and chemical shift of a hydrogen bonded directly to X increase. 

The order of acidity of these four classes of compounds is alcohols enols phenols carboxylic acids. Therefore, it 

Finally, it is important to recognize that hydrogen bonding can be either intermolecular (X-H and Y are part of separate molecules) or intramolecular (X-H and Y are part of the same molecule). 

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HETCOR (Section 13 19) A 2D NMR technique that correlates the H chemical shift of a proton to the chemical shift of the carbon to which it is attached HETCOR stands for heteronuclear chemical shift correlation Heteroatom (Section 1 7) An atom in an organic molecule that IS neither carbon nor hydrogen Heterocyclic compound (Section 3 15) Cyclic compound in which one or more of the atoms in the nng are elements other than carbon Heterocyclic compounds may or may not be aromatic... 

B. Calculate the total number of hydrogen atoms on the carbon atoms, and see if this fits with the number of hydrogen atoms in the molecule. When you have allowed for identical groups, any hydrogen left must be attached to an element other than carbon. 

When a molecule contains an element other than carbon or hydrogen, those atoms, called heteroatoms, are shown explicitly in the skeletal structure. Furthermore, while the hydrogens attached to carbon atoms typically are not shown, hydrogens attached to heteroatoms are shown, as illustrated by the molecule ethylamine in the following ... 

Carboranes. The accumulation of charge observed in borane anions discussed above may also be afforded by changing some boron atoms by other elements with more valence electrons than boron. The best known examples of this kind of isoelectronic compound are the carboranes. The most important series of carboranes is that with molecular formulas C2B 2Hn, the dicarba-c/oso-boranes, where n is any integer from 5 to 12. These neutral species are isoelectronic with the borane anions BnH . The structures of these compounds are closed deltahedra with terminal hydrogen atoms attached to each carbon or... 

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