How do you draw #C_8H_18# (octane)? How many isomers are there? What are the names of the isomers?

Answer 1

Including stereoisomers, there are 24 stereoisomers of #"C"_8"H"_18#.

You work systematically. First, draw the straight-chain octane.

  • Octane

    Next, draw all the heptanes. They will have a methyl group.

    • 2-Methylheptane
    • 3-Methylheptane (2 enantiomers)
    • 4-Methylheptane

      Next, come the hexane isomers. They will have either two methyl groups or an ethyl group.

      All the isomers with a methyl group on carbon 2.

      • 2,2-Dimethylhexane
      • 2,3-Dimethylhexane (2 enantiomers)
      • 2,4-Dimethylhexane (2 enantiomers)
      • 2,5-Dimethylhexane

        Then, all the isomers with a methyl group on carbon 3.

        • 3,3-Dimethylhexane
        • 3,4-Dimethylhexane (2 enantiomers + 1 meso compound)

          Then, the isomers with an ethyl group

          • 3-Ethylhexane

            Now we draw the pentanes. They will have either three methyl groups or an ethyl and a methyl.

            Isomers with three methyl groups. The possible patterns are 2,2,3, 2,2,4, 2,3,3 and 2,3,4.

            • 2,2,3-Trimethylpentane (2 enantiomers)
            • 2,2,4-Trimethylpentane (isooctane)
            • 2,3,3-Trimethylpentane
            • 2,3,4-Trimethylpentane

              Then the ethylmethylpentanes.

              • 3-Ethyl-2-methylpentane
              • 3-Ethyl-3-methylpentane

                Finally, the butanes.

                There is only one possibility.

                • 2,2,3,3-Tetramethylbutane

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Answer 2

To draw C8H18 (octane), you would arrange 8 carbon atoms in a straight chain, with each carbon atom forming four bonds, and then attach hydrogen atoms to each carbon atom to satisfy their valency.

The isomers of octane are:

  1. n-Octane (normal octane)
  2. 2-Methylheptane
  3. 3-Methylheptane
  4. 4-Methylheptane
  5. 2,2-Dimethylhexane
  6. 2,3-Dimethylhexane
  7. 2,4-Dimethylhexane
  8. 3,3-Dimethylhexane
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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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