You may notice that the abbreviations for the names of carbon chains look very much like the symbols for chemical elements: this is deliberate, and these symbols are sometimes called ‘organic elements. They can be used in chemical structures just like element symbols. It is often convenient to use the ‘organic element’ symbols for short carbon chains for tidiness. Here are some examples. Structure 1 to the right shows how we drew the structure of the amino acid methionine on p. 20. The stick representing the methyl group attached to the sulfur atom does, however, look a little odd. Most chemists would draw methionine as structure 2, with ‘Me’ representing the CH3 (methyl) group. Tetraethyllead used to be added to petrol to prevent engines ‘knocking’, until it was shown to be a health hazard. Its structure (as you might easily guess from the name) is easy to write as PbEt4 or Et4Pb. Remember that these symbols (and names) can be used only for terminal chains of atoms. We couldn’t abbreviate the structure of lysine to 3, for example, because Bu represents 4 and not 5.

Before leaving carbon chains, we must mention one other very useful organic element symbol, R. R in a structure can mean anything—it’s a sort of wild card. For example, structure 6 would indicate any amino acid, if R = H it is glycine, if R = Me it is alanine... As we’ve men tioned before, and you will see later, the reactivity of organic molecules is so dependent on their functional groups that the rest of the molecule can be irrelevant. In these cases, we can choose just to call it R.

مواضيع ذات صلة

Chemical reactions

Rotation and rigidity

The carbonyl group

We can hybridize any atoms

Hybridization of atomic orbitals

Molecular orbitals of molecules with more than two atoms

Other factors affecting degree of orbital interaction

Bonds between different atoms

Forming bonds using 2s and 2p atomic orbitals: σ and π orbitals

Bond order

Why hydrogen is diatomic but helium is not

Breaking bonds