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Homework Help: Would this be a picture of pentene?

  1. May 9, 2014 #1


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    1. The problem statement, all variables and given/known data

    Would this be a picture of pentene?

    I'm unsure because of the location of the double bond - does the location of the double bond factor into naming alkenes?

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  2. jcsd
  3. May 9, 2014 #2


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    Location of the double bond matters, just like the side chain matters. But yes, technically it is a substituted pentene. At the same time it is an isomer of hexene.
  4. May 9, 2014 #3


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    Thank you! I looked up the nomenclature rules for alkenes and they are:

    1) Find longest carbon chain. In this case that would be the 5-carbon chain (pentene).
    2) Number longest carbon chain so that the double bonded carbons have the lowest numbers.
    3) If the double-bonded carbons are equidistant from the ends, then number so that the first substituent has the lowest number.
    4) Name substituents and and chain as appropriate (follow rules for alkanes now)
    5) If more than one double bond is present, indicate positions using numbers and add appropriate suffixies (i.e. -diene). In this case there is only one double bond.

    So would the systematic name be: 4-methyl-2-pentene? I numbered so that the double-bonded carbons get the lowest numbers. I also forgot to mention above that the position of the double bond must be mentioned in the systematic name.
    Last edited: May 9, 2014
  5. May 10, 2014 #4


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    Although you are right in nomenclature, I'd say in my personal opinion, you can put the number corresponding to the position of multiple bond after the root (chain length). This way, if there are both double and triple bond present, it looks tidy.

    For eg. 4-methylpent-2-ene.
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