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3.4.3: Condensed Structural and Line-Angle Formulas

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    • Anonymous
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    Learning Objectives
    • Write condensed structural formulas for alkanes given complete structural formulas.
    • Draw line-angle formulas given structural formulas.

    We use several kinds of formulas to describe organic compounds. A molecular formula shows only the kinds and numbers 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 isobutane. A structural formula shows all the carbon and hydrogen atoms and the bonds attaching them. Thus, structural formulas identify the specific isomers by showing the order of attachment of the various atoms.

    Unfortunately, structural formulas are difficult to type/write and take up a lot of space. Chemists often use condensed structural formulas to alleviate these problems. The condensed formulas show hydrogen atoms right next to the carbon atoms to which they are attached, as illustrated for butane:

    1b6bba3434534db0888ddeb47ba199d8.jpg

    The ultimate condensed formula is a line-angle formula, in which carbon atoms are implied at the corners and ends of lines, and each carbon atom is understood to be attached to enough hydrogen atoms to give each carbon atom four bonds. For example, we can represent pentane (CH3CH2CH2CH2CH3) and isopentane [(CH3)2CHCH2CH3] as follows:

    line-angle formula.jpg

    Parentheses in condensed structural formulas indicate that the enclosed grouping of atoms is attached to the adjacent carbon atom. 

    Example \(\PageIndex{1}\)

    Write the condensed formula for each of the following structural formulas.


    1. clipboard_ef6870e4100a4e847c30ac55257ed5d5a.png

    2. clipboard_e487ef38d4ac337f2df65c326e705cbfa.png

    3. clipboard_ee5e482d0e71771e3edd46d2c3e1b1648.png
    Answer a

    CH3CH3 

    Answer b

    CH3CH2CH3 

    Answer c

    CH3CH2CH2CH2CH3 

    Exercise \(\PageIndex{1}\)

    Complete the following translations between complete structural formulas, condensed structural formulas, and line-angle formulas. 

    1. A condensed structural formula for isohexane can be written as (CH3)2CHCH2CH2CH3. Draw the line-angle formula for isohexane. 
    2. Draw the line-angle formula for the compound CH3CH2CH(CH3)CH2CH2CH3. 
    3. Give the structural formula for the compound represented by this line-angle formula:
      clipboard_eda05bac1d8631d2cd84ddb9b74d14436.png
    Answer a

    The longest chain should contain five carbon atoms in a row; the carbon atom on the end has a branch to another carbon.

    Answer b

    The longest chain should contain six carbon atoms in a row; the third carbon atom has a branch to another carbon.

    Answer c

    (CH3)2CHCH2CH(CH3)CH2CH3 

     

    Key Takeaways

    • Condensed chemical formulas show the hydrogen atoms (or other atoms or groups) right next to the carbon atoms to which they are attached.
    • Line-angle formulas imply a carbon atom at the corners and ends of lines. Each carbon atom is understood to be attached to enough hydrogen atoms to give each carbon atom four bonds.

    This page titled 3.4.3: Condensed Structural and Line-Angle Formulas is shared under a CC BY-NC-SA 3.0 license and was authored, remixed, and/or curated by Anonymous via source content that was edited to the style and standards of the LibreTexts platform.