Using conventional bond notation, you could draw it as, for example: To do this, the bonds are shown using conventional symbols:įor example, you might want to show the 3-D arrangement of the groups around the carbon which has the -OH group in butan-2-ol. There are occasions when it is important to be able to show the precise 3-D arrangement in parts of some molecules. How to draw structural formulae in 3-dimensions If you made a model of one of them, you could turn it into any other one simply by rotating one or more of the carbon-carbon bonds. All of the following represent exactly the same molecule. It does not matter in the least whether you draw any side groups pointing up or down. Anything else is simply hung off that chain. To overcome this possible confusion, the convention is that you always look for the longest possible chain of carbon atoms, and then draw it horizontally. If you had a model, the only difference between these three diagrams is that you have rotated some of the bonds and turned the model around a bit. That's exactly the same as the other two structures. There are four carbons joined up in a row, with a CH 3 group attached to the next-to-end one. The other one isn't so obvious until you look at the structure in detail. The two structures on the left are fairly obviously the same - all we've done is flip the molecule over. The following structures again all represent the same molecule - 2-methylbutane. This is even more important when you start to have branched chains of carbon atoms. The convention is that we draw it with all the carbon atoms in a straight line - as in the first of the structures above. Not one of the structural formulae accurately represents the shape of butane. The only difference is that there has been some rotation about some of the carbon-carbon bonds. The next three structures all represent butane.Īll of these are just versions of four carbon atoms joined up in a line. Remember from above that these two structures both represent the same molecule: You still have to be careful in drawing structures in this way. You do, however, lose something by condensing the acid group in this way, because you can't immediately see how the bonding works. You could even condense it further to CH 3COOH, and would probably do this if you had to write a simple chemical equation involving ethanoic acid. For example, ethanoic acid would be shown in a fully displayed form and a simplified form as: You can simplify the formula by writing, for example, CH 3 or CH 2 instead of showing all these bonds. The commonest way to draw structural formulaeįor anything other than the most simple molecules, drawing a fully displayed formula is a bit of a bother - especially all the carbon-hydrogen bonds. The displayed formula could be written as either of these:īut, again these are exactly the same. Consider a slightly more complicated molecule, C 2H 5Cl. One structure is in reality a simple rotation of the other one. But these two structures are actually exactly the same. The chlorines could be opposite each other or at right angles to each other. You might think that there were two different ways of arranging these atoms if you drew a displayed formula. For example, consider the simple molecule with the molecular formula CH 2Cl 2. This mismatch between what you draw and what the molecule actually looks like can lead to problems if you aren't careful. Notice that the way the methane is drawn bears no resemblance to the actual shape of the molecule. For example, this is a model of methane together with its displayed formula: You need to remember that each line represents a pair of shared electrons. \)Ī displayed formula shows all the bonds in the molecule as individual lines.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |