[nameless74]

I have a test on Monday and I'm so behind on naming hydrocarbons. Teacher gave us a work sheet to study on the weekend but I'm having a problem. He did 1 question which i'm trying to understand.

                 CH3
                  |
CH3 - CH2 - CH - CH - CH3
                         |
                        CH2
                         |
                        CH3

Okay, I know that the longest chain of carbon is 6 which is hexane. Well the next step I'm kind off confused about where to start. Is it going to be from left to right. I've been searching some example about naming hydrocarbons and some they start from left to right or right to left. I get some right but mostly wrong. Like the one example that i gave you. My answer would be:

3rd carbon there is 1 carbon so it would be 3 methyl
4th carbon there is 2 carbons so it would be 4 ethyl

so my answer would be 3-methyl, 4-ethyl hexane
which is wrong the answer should be 3, 4 dimethyl hexane

another example from the book:

             CH2CH3
             |
CH3 - CHCHCHCH3
         |      |
   CH3CH2   CH3

the longest chain of carbon is 6 which is hexane.
i startet the carbons from left to right so
2nd carbon has 2 carbons - 2 ethyl
3rd carbon has 2 carbons - 2 ethyl
4th carbon has 1 carbon - 4 methyl

so the answer would be 4 methyl, 2 ethyl, 2 ethyl hexane or 4 methyl, diethyl hexane

and the right answer was 2,4-dimethyl-3-ethylhexane.

i spent the night trying some example and its frustrating just spending 2 hours for 1 example that i couldn't get the right answer. i need helpppppp .   SadSadSadSad

[Floreaa]

                     CH3
                      |
CH3⁶ - CH2⁵ - CH⁴ - CH³ - CH3
                              |
                              CH2²
                              |
                              CH3¹


OK. Indeed the parent chain has 6 carbons so it will be hex-. I have bolded the parent chain, in order for us to be easier to see. You will start the numbering from right to left (from the red glowing group to the green glowing group) this time cause the IUPAC rule says that the sum of the numbers that substituents have (in this case 2 methyl groups) should be as small as possible. So one methyl group will have number 3 and the other will have number 4. Because we have 2 methyl groups we will use the prefix di- before the name of the substituent.

So, all in all it will be: 3,4-dimethylhexane

For the next compound I'll let you work it out. If you need further help you can look up into the blue book of nomenclature of organic compounds. http://www.acdlabs.com/iupac/nomenclature/ And jut for the acyclic hydrocarbons http://www.acdlabs.com/iupac/nomenclature/79/r79_5.htm

Hope it helped.

[Borek]

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