How to Interpret and Write Structural Formulas

Shapes of Molecules and Ions from VSEPR Theory 

Bonding Nonbonding Total Central Atom or Ion Examples 

Organic chemists use a variety of ways to write structural formulas. The most common types of representations are shown in Fig. 1.37 using propyl alcohol as an example. The dot structure shows all of the valence electrons, but writing it is tedious and time-consuming. The other representations are more convenient and are, therefore, more often used. 

Sometimes we even omit unshared pairs when we write formulas. However, when we write chemical reactions, we see that it is necessary to include the unshared electron pairs when they participate in the reaction. It is a good idea, therefore, to get into the habit of writing the unshared (nonbonding) electron pairs in the structures you draw. 

If we look at the model for propyl alcohol given in Fig. 1.37fl and compare it with the dot, dash, and condensed formulas in Figs, 31b-d we find that the chain of atoms is straight in those formulas. In the model, which corresponds more accurately to the actual shape of the molecule, the chain of atoms is not at all straight. Also of importance is this Atoms joined by single bonds can rotate relatively freely with respect to one another. (We discussed this point briefly in Section 1.12B.) This relatively free rotation means that the chain of atoms in propyl alcohol can assume a variety of arrangements like these  

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