Displaying molecules using a skeletal representation Displaying molecules using a skeletal representation The skeletal representation makes use of the fact that carbon and hydrogen are the most common elements in organic compounds, and also that carbon almost always forms four covalent bonds. (A) The process of converting a displayed formula into a skeletal formula has three stages: (i) the molecule is drawn with the carbon chain ‘staggered’ in a zigzag; this is important to allow correct identification of the number of carbon atoms in the final molecule and is a better representation of the actual bond angles. (ii) The ‘C’ label for carbon atoms is omitted. (iii) The ‘H’ label for hydrogen atoms is omitted only for hydrogen atoms bonded to carbon. When interpreting a skeletal formula, we assume that carbon will make four bonds; if a carbon appears to make fewer than four bonds in the skeletal representation, then the ‘missing’ bonds are assumed to be to hydrogen atoms. Using the skeletal representation highlights the heteroatoms present in the molecule and becomes particularly useful once we consider how to display different isomers. (B) The guidelines for drawing skeletal structures are relatively flexible and in some cases, for example where we wish to draw attention to a particular group of atoms, the ‘C’ symbol for some of the carbon atoms may be shown. It is important not to omit any hydrogen atoms bonded to carbon atoms that are explicitly displayed in this way. (C) Wedge and hashed bonds can be used to illustrate the direction of bond vectors relative to the plane of the page. Amanda L. Jonsson et al. Essays Biochem. 2017;61:401-427 ©2017 by Portland Press Ltd