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Nomenclature of Alkanes II

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    I. The parent compound must have the longest chain of carbon atoms

    Learn: methane (1 carbon atom), ethane (2 carbon atoms), propane (3 carbon atoms), butane (4 carbon atoms), pentane (5 carbon atoms), hexane (6 carbon atoms), heptane (7 carbon atoms), octane (8 carbon atoms), nonane (9 carbon atoms) and decane (10 carbon atoms).

    Try to name the following compounds:

    1. CH3-CH2-CH2-CH3
    2. CH3-CH2-CH2-CH2-CH2-CH3
    3. CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH2-CH3

    Try to draw structures for the following compounds:

    1. propane
    2. pentane
    3. octane

    II. The parent chain is numbered to give substituents the lowest possible numbers

    Substituent names are methyl, ethyl, propyl, butyl, etc. The number showing the point of attachment to the parent chain precedes the substituent name. If you have more than one substituent with the same name, a number of attachment must be given for each substituent and the number of the substituents must be designated with di-, tri-, etc.

    Try to name the following compounds...

    7. alkanenomenclature1.gif

    8. alkanenomenclature2.gif

    9. alkanenomenclature3.gif

    Try to draw structures for the following compounds...

    1. 2,2-dimethylpropane
    2. 3-methylheptane
    3. 4,5-diethylnonane

    III. Substituents are named in alphabetical order

    Remember that the numbering of the parent chain must give all substituents the lowest possible numbers regardless of their names.

    Try to name the following compound...

    13. alkanenomenclature4.gif

    IV. A large substituent is numbered to give its point of attachment

    The point of attachment is number one and any other smaller groups are named as substituent groups on the larger group. This numbering is independent of the numbering of the parent chain. Try to name the following compounds...

    14.

    alkanenomenclature5.gif

    15. alkanenomenclature6.gif

    Try to draw structures for the following compounds...

    1. 4-(1-methylethyl)heptane
    2. 5-(1,1-dimethylethyl)nonane

    V. Ring compounds are designated with a cyclo- prefix and are numbered to give multiple substituents the lowest possible numbers

    A single substituent does not need to be numbered. A ring can also be named as a substituent. Try to name the following compounds:

    18. alkanenomenclature7.gif

    19. alkanenomenclature8.gif

    20. alkanenomenclature9.gif

    Try to draw structures for the following compounds...

    1. ethylcyclobutane
    2. 1-ethyl-4-methylcyclohexane
    3. cyclobutylcyclooctane

    VI. Common Names

    • isopropyl = 1-methylethyl
    • isobutyl = 2-methylpropyl
    • sec-butyl = 1-methylpropyl
    • tert-butyl = 1,1-dimethylethyl
    • neo-pentyl = 2,2-dimethylpropyl
    • iso-pentyl = 3-methylbutyl

    Try to name the following compounds using common names...

    24. alkanenomenclature10.gif

    25. alkanenomenclature11.gif

    Try to draw structures for the following compounds...

    1. 4-isopropyloctane
    2. isopentylcyclohexane

    Answers

    1. butane
    2. hexane
    3. nonane
    4. CH3-CH2-CH3
    5. CH3-CH2-CH2-CH2-CH3
    6. CH3-CH2-CH2-CH2-CH2-CH2-CH2-CH3
    7. 2-methylbutane
    8. 3-ethylhexane
    9. 3-methyloctane (Remember that you must number the parent chain to give the substituent the lowest possible number.)
    10. alkanenomenclature12.gif
    11. alkanenomenclature13.gif
    12. alkanenomenclature14.gif
    13. 4-ethyl-3-methylheptane
    14. 4-(1-methylethyl)octane
    15. 5-(1-methylpropyl)decane
    16. alkanenomenclature15.gif
    17. alkanenomenclature16.gif
    18. 1-ethyl-2-methylcyclohexane
    19. methylcyclopentane (You do not need a number since there is only one substituent and it is assumed to be on the first carbon regardless of how the ring compound is drawn.)
    20. cyclopropylcyclopentane
    21. alkanenomenclature17.gif
    22. alkanenomenclature18.gif
    23. alkanenomenclature19.gif
    24. neo-pentylcycloheptane (1-(2,2-dimethyl-1-propyl)cycloheptane is the proper name.)
    25. isopropylcyclohexane
    26. alkanenomenclature20.gif
    27. alkanenomenclature21.gif

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