When we draw organic structures, we try to be as realistic as we can be without putting in superfluous detail. Look at these three pictures.

(1) is immediately recognizable as Leonardo da Vinci’s Mona Lisa. You may not recognize

 (2)—it’s also Leonardo da Vinci’s Mona Lisa—this time viewed from above. The frame is very ornate, but the picture tells us as much about the painting as our rejected linear and 90° angle diagrams did about our fatty acid. They’re both correct—in their way—but sadly useless. What we need when we draw molecules is the equivalent of (3). It gets across the idea of the original, and includes all the detail necessary for us to recognize what it’s a picture of, and leaves out the rest. And it was quick to draw—this picture was drawn in less than 10 minutes: we haven’t got time to produce great works of art! Because functional groups are the key to the chemistry of molecules, clear diagrams must emphasize the functional groups and let the hydrocarbon framework fade into the back ground. Compare the diagrams below:

The second structure is the way that most organic chemists would draw linoleic acid. Notice how the important carboxylic acid functional group stands out clearly and is no longer cluttered by all those Cs and Hs. The zig-zag pattern of the chain is much clearer too. And this structure is much quicker to draw than any of the previous ones! To get this diagram from the one above we’ve done two things. Firstly, we’ve got rid of all the hydrogen atoms attached to carbon atoms, along with the bonds joining them to the carbon atoms. Even without drawing the hydrogen atoms we know they’re there—we assume that any carbon atom that doesn’t appear to have its potential for four bonds satisfi ed is also attached to the appropriate number of hydrogen atoms. Secondly, we’ve rubbed out all the Cs representing carbon atoms. We’re left with a zig-zag line, and we assume that every kink in the line represents a carbon atom, as does the end of the line.

مواضيع ذات صلة

Organometallics as bases

How to make organolithium reagents

Making organometallics, How to make Grignard reagents

Organometallic compounds contain a carbon–metal bond

Lewis acids and bases

pKa in action—the development of the drug cimetidine

Why do we need to compare acid strengths of O and N acids?

Carbon acids

Substituents affect the pKa

The ‘pKas’ of bases

Nitrogen compounds as acids and bases

Delocalization of the negative charge stabilizes the conjugate base