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    This is a bit above the AS level syllabus since we only really need to know up to hexane and the isomers we are given are relatively simple, but I'm really curious about how some of the more complex molecules are named. I have an example, imagine nonane but then you add on a 2,2-dimethylpropanol onto the fifth carbon of the nonane, what would it be called? Also, when naming alkanes, do you ALWAYS choose the longest chain, or do you choose the longest chain with a functional group?

    Would it be called: 5-(2,2-dimethylpropanol)nonane?
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    Always longest.

    If you added R (where R = 2,2...) onto the 5th carbon then you would get 5-Rnonane in your example.

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    nope - if you draw out the molecule, you'll see that it's basically 2,2-dimethyloctan-1-ol with a butyl group on C4 - therefore 4-butyl-2,2-dimethyloctan-1-ol
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    (Original post by megeggan)
    nope - if you draw out the molecule, you'll see that it's basically 2,2-dimethyloctan-1-ol with a butyl group on C4 - therefore 4-butyl-2,2-dimethyloctan-1-ol
    So does that mean you take the longest carbon chain with the functional group as opposed to the 9 carbons in a chain? Also, I get what you're saying, but wouldn't it be a butyl group on C5? Because if it was on C4, then it wouldn't be octan-1-ol, it would be heptan-1-ol with a pentyl group attached right? Or have I totally messed it up?
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    I agree with megeggan that it is 4-butyl-2,2-dimethyloctan-1-ol. Essentially what you do is take the functional group and find the longest chain of carbons you can make starting with the functional group on it. In this case it is 8 carbons which is where the octanol bit comes from. The end of this longest carbon chain which is nearest the (highest priority) functional group is always the 1 position. In this molecule it is at the end of this chain so the OH is on the 1 position. So counting back along the chain, what you called the 5 position before in nonane is now the 4 position, which is where the butyl side chain is. I've tried to illustrate this below rather crudely.

    (8 position this side) CH3-CH2-CH2-CH2-CH(C4H9)-CH2-C(CH3)-CH2OH (1 position this side)
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    (Original post by Kyri)
    I agree with megeggan that it is 4-butyl-2,2-dimethyloctan-1-ol. Essentially what you do is take the functional group and find the longest chain of carbons you can make starting with the functional group on it. In this case it is 8 carbons which is where the octanol bit comes from. The end of this longest carbon chain which is nearest the (highest priority) functional group is always the 1 position. In this molecule it is at the end of this chain so the OH is on the 1 position. So counting back along the chain, what you called the 5 position before in nonane is now the 4 position, which is where the butyl side chain is. I've tried to illustrate this below rather crudely.

    (8 position this side) CH3-CH2-CH2-CH2-CH(C4H9)-CH2-C(CH3)-CH2OH (1 position this side)
    It's not quite as simple as this.

    The functional group is not always given priority, only when it is a terminating group (such as acid, aldehyde etc)

    Otherwise the longest carbon chain is found and used as the root.
    In the case of the alcohol group it is not terminating and not given priority. The longest carbon chain however is numbered to give the hydroxy attachment the lowest number.
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    (Original post by charco)
    It's not quite as simple as this.

    The functional group is not always given priority, only when it is a terminating group (such as acid, aldehyde etc)

    Otherwise the longest carbon chain is found and used as the root.
    In the case of the alcohol group it is not terminating and not given priority. The longest carbon chain however is numbered to give the hydroxy attachment the lowest number.
    What do you mean by 'terminating'? And if that is not the case here, then what would it actually be called? Because I finally know what they mean now by 4-butyl-2,2-dimethyloctan-1-ol.
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    (Original post by Webbykun)
    What do you mean by 'terminating'? And if that is not the case here, then what would it actually be called? Because I finally know what they mean now by 4-butyl-2,2-dimethyloctan-1-ol.
    A terminating group simply stops the chain by having nowhere else to go. You cannot attach anything else to a -COOH or a -CHO group apart form the alkyl chain they terminate, they have to be at the end of a chain and for that reason they are high priority.
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    (Original post by charco)
    It's not quite as simple as this.

    The functional group is not always given priority, only when it is a terminating group (such as acid, aldehyde etc)

    Otherwise the longest carbon chain is found and used as the root.
    In the case of the alcohol group it is not terminating and not given priority. The longest carbon chain however is numbered to give the hydroxy attachment the lowest number.
    The OH is on a terminating carbon if we take the 8 carbon chain coming off of it, although I do see that it isn't if we take the base name as the 9 carbon chain, so I still think it's 4-butyl-2,2-dimethyloctan-1-ol. I just checked with the auto naming feature of chemdraw and it also comes up with that name. I think it comes up with the proper IUPAC name. Not 100% sure though. What would you call it?
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    How about... (given the necessity of the name using the longest continuous carbon chain...):

    5-(3'-hydroxy-2',2'-dimethylpropyl)nonane?
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    (Original post by cpchem)
    How about... (given the necessity of the name using the longest continuous carbon chain...):

    5-(3'-hydroxy-2',2'-dimethylpropyl)nonane?
    That certainly sounds reasonable. Another one I can come up with is 5-(3'-hydroxyneopentyl)nonane. I always thought when there was just one functional group in a molecule it always took the suffix of the name, unless there are more than one, in which case the one with highest priority gets the suffix. Maybe I'm wrong. I'd like to see what charco thinks it is.

    EDIT: Just to to add that ISIS draw also names that molecule as 4-butyl-2,2-dimethyloctan-1-ol.
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    (Original post by Kyri)
    That certainly sounds reasonable. Another one I can come up with is 5-(3'-hydroxyneopentyl)nonane. I always thought when there was just one functional group in a molecule it always took the suffix of the name, unless there are more than one, in which case the one with highest priority gets the suffix. Maybe I'm wrong. I'd like to see what charco thinks it is.

    EDIT: Just to to add that ISIS draw also names that molecule as 4-butyl-2,2-dimethyloctan-1-ol.
    As I noted earlier, the rules of nomenclature are pretty complicated and I certainly am no expert.

    However, the priority comes from rule 13.1 (Seniority of chains rule) of the IUPAC nomenclature.

    For info I'll copy them here:

    13.1 -In an acyclic compound, that chain upon which the nomenclature and numbering are based is called the "principal chain". When in an acyclic compound there is a choice for principal chain, the following criteria are applied successively, in the order listed, until a decision is reached:

    a) Maximum number of substituents corresponding to the principal group

    b) Maximum number of double and triple bonds considered together

    c) Maximum length

    d) Maximum number of double bonds

    e) Lowest locants for the principal groups (that is, for the suffix).

    f) Lowest locants for multiple bonds.

    g) Lowest locants for double bonds

    h) Maximum number of substituents cited as prefixes

    i) Lowest locants for all substituents in the principal chain cites as prefixes

    j) The substituent first cited in alphabetical order

    k) Lowest locants for the substituent cited first as prefix in alphabetical order


    And so the alcohol group (a) is the principal group and takes priority over the maximum chain length (c).

    So the correct name is: 4-butyl-2,2-dimethyloctan-1-ol.
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    (Original post by charco)
    As I noted earlier, the rules of nomenclature are pretty complicated and I certainly am no expert.

    However, the priority comes from rule 13.1 (Seniority of chains rule) of the IUPAC nomenclature.

    For info I'll copy them here:

    13.1 -In an acyclic compound, that chain upon which the nomenclature and numbering are based is called the "principal chain". When in an acyclic compound there is a choice for principal chain, the following criteria are applied successively, in the order listed, until a decision is reached:

    a) Maximum number of substituents corresponding to the principal group

    b) Maximum number of double and triple bonds considered together

    c) Maximum length

    d) Maximum number of double bonds

    e) Lowest locants for the principal groups (that is, for the suffix).

    f) Lowest locants for multiple bonds.

    g) Lowest locants for double bonds

    h) Maximum number of substituents cited as prefixes

    i) Lowest locants for all substituents in the principal chain cites as prefixes

    j) The substituent first cited in alphabetical order

    k) Lowest locants for the substituent cited first as prefix in alphabetical order


    And so the alcohol group (a) is the principal group and takes priority over the maximum chain length (c).

    So the correct name is: 4-butyl-2,2-dimethyloctan-1-ol.
    Cool . Thanks for going through that.
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    Yeah thanks a lot all of you . It's been on my mind if other things could have priority over longest chains and now I know , thanks again everyone.
 
 
 
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