12.4: Drawing Organic Structures

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Page ID: 401279

Lisa Sharpe Elles
University of Kansas

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Learning Objectives

Draw condensed structures and line structures for simple compounds from the given molecular formulas.
Convert between expanded, condensed and line structures.

We use several kinds of formulas to describe organic compounds. A molecular formula shows only the number and type of atoms in a molecule. For example, the molecular formula C₄H₁₀ tells us there are 4 carbon atoms and 10 hydrogen atoms in a molecule, but it doesn’t distinguish between butane and 2-methylpropane. A structural formula shows all the carbon and hydrogen atoms and the bonds attaching them (expanded structure). This type of structure allows for easy identification of specific isomers by showing the order of attachment of the various atoms.

Unfortunately, structural formulas that show the bonds between all atoms are sometimes difficult to type/write and take up a lot of space, especially when the number of atoms greatly increases. Chemists often use condensed structures, that show hydrogen atoms right next to the carbon atoms to which they are attached, to alleviate these problems. The ultimate condensed formula is a line (or line-angle) structure, in which carbon atoms are implied at the corners and ends of lines rather than written out, and each carbon atom is understood to be attached to the appropriate amount of hydrogen atoms to give each carbon atom four bonds. Parentheses in condensed structural formulas indicate that the enclosed grouping of atoms is attached to the adjacent carbon atom. All three of these structure types are illustrated for butane and its isomer, 2-methylpropane in Figure \(\PageIndex{1}\) below.