Naming Alkanes, Alkenes, and Alkynes

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Hydrocarbons - Naming and Writing Chemical Formulas

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Key Questions

  • IUPAC stands for International Union for Pure and Applied Chemistry.

    With this system, prefixes are used to tell the number of carbons in the parent chain (the longest string of carbons) as well as branch chains (carbons and hydrogens that branch off the parent chain).

    The prefixes are:

    • 1 carbon = meth
    • 2 carbons = eth
    • 3 carbons = prop
    • 4 carbons = but
    • 5 carbons = pent
    • 6 carbons = hex
    • 7 carbons = hept
    • 8 carbons = oct
    • 9 carbons = non
    • 10 carbons = dec

    Next, you would add endings such as:

    • -ane for an alkane (all single bonds)
    • -ene for an alkene (one double bond)
    • -diene ( 2 double bonds)
    • -yne (one triple bond)

    Depending on how many carbons are in the hydro-carbon branch, you would use the above mentioned prefix (meth, eth, prop, etc) along with a -yl ending.

    If you have halogen #(F, Cl, Br, I)# branches you name them first in alphabetical order than the hydrocarbon (alkyl) branches next in alphabetical order (ex. but, eth, meth, prop etc). If you have more than one of the same type of branch, like two methyl branches or two chlorine branches then you preceed the branch name with di- , tri-, tetra-, penta- etc.

    In addition you need to place a number in front of the branch names to indicate where off the parent chain they are coming from. When naming a branched alkane, you may have to number your parent chain of carbons from right to left or left to right so the branches get the lowest count.

    With a Alkene, Alkadiene, or Alkyne, the double or triple bonds in the parent chain get the lowest count and then you keep that count when siting the parent chain carbons that the branches come off of.

  • This video provides a basic introduction to naming alkenes and alkynes.

  • This video provides a very basic introduction to naming alkanes.


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