![]() ![]() 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. So 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. ![]() It's cheaper, but more difficult to get the bond angles right.Ĭonsider a slightly more complicated molecule, C 2H 5Cl. Share the cost with some friends, keep it in good condition and don't lose any bits, and resell it via eBay or Amazon at the end of your course.Īlternatively, get hold of some coloured Plasticene (or other children's modelling clay) and some used matches and make your own. Google molymod to find a supplier and more about them, or search for molymod on Amazon. ![]() An introductory organic set is more than adequate. The models made by Molymod are both cheap and easy to use. If your school or college hasn't given you the opportunity to play around with molecular models in the early stages of your organic chemistry course, you might consider getting hold of a cheap set. Note: This is all much easier to understand if you have actually got some models to play with. 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. This mismatch between what you draw and what the molecule actually looks like can lead to problems if you aren't careful.įor example, consider the simple molecule with the molecular formula CH 2Cl 2. Notice that the way the methane is drawn bears no resemblance to the actual shape of the molecule. You need to remember that each line represents a pair of shared electrons.įor example, this is a model of methane together with its displayed formula: There are various ways of drawing this and you will need to be familiar with all of them.Ī displayed formula shows all the bonds in the molecule as individual lines. In cases like this, the bonding in the organic molecule isn't important.Ī structural formula shows how the various atoms are bonded. About the only place where you might come across them is in equations for the combustion of simple hydrocarbons, for example: Molecular formulae are very rarely used in organic chemistry, because they don't give any useful information about the bonding in the molecule. This page explains the various ways that organic molecules can be represented on paper or on screen - including molecular formulae, and various forms of structural formulae.Ī molecular formula simply counts the numbers of each sort of atom present in the molecule, but tells you nothing about the way they are joined together.įor example, the molecular formula of butane is C 4H 10, and the molecular formula of ethanol is C 2H 6O. ![]()
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