Quick doubt on organic nomeclature

[Munfred]

Hi

When naming organic compounds, hydrocarbons for example, it's very common to have several radicals of the same group attached to the 'main' carbon line. So for example, pentane, with 5 carbons in a row. Suppose we add 2 methyl to it, one on carbon 2 and one or carbon 3. We'd then have to call it 2,3 dimethyl-pentane. Or suppose we add 2 methyl on carbon 2 and 2 more on carbon 3, it'd then be 2,2,3,3 tetramethyl-pentane.

So my question is: if we have several radicals of the same group, do we always have to put the di, tri, tetra or whatever prefix before the group name? Like in the above examples, dimethyl, tetramethyl, because I assume that one can simply count how many methyl's we have on the molecule. So I don't see much of a purpose on adding a prefix. Also, instead of using di or tri, can we just use a number, like 2,3 2-dimethyl-pentane? Or it could cause ambiguity?

Thanks in advance

 

[chemisttree]

So my question is: if we have several radicals of the same group, do we always have to put the di, tri, tetra or whatever prefix before the group name? Like in the above examples, dimethyl, tetramethyl, because I assume that one can simply count how many methyl's we have on the molecule. So I don't see much of a purpose on adding a prefix. Also, instead of using di or tri, can we just use a number, like 2,3 2-dimethyl-pentane? Or it could cause ambiguity?

Thanks in advance

You could do it your way and name the 2,2,3,3-tetramethylpentane just 2,2,3,3-methylpentane IF... everyone did it that way and knew that you have to count the number of substitutions (2,2,3,3- would be 4, for example) and know that there are 4 of the radical that follows (-methylpentane). That's not the way it's done but it could be.

Of course we would all have to learn yet another weird numbering system and remember that the preceeding numbers refer only to the radical(s) they are associated with.

 

[Blueshift5]

Dear student,

Thank you for your question regarding organic nomenclature. The use of prefixes such as di, tri, and tetra before the group name is necessary to accurately represent the structure of the molecule. While it may seem redundant to use these prefixes when the number of groups can easily be counted, it is important for consistency and clarity in naming organic compounds.

Using numbers instead of prefixes can cause ambiguity, as the position of the groups on the carbon chain must also be specified. In your example, using 2,3 2-dimethyl-pentane could be interpreted as having two methyl groups on carbon 2 and one on carbon 3, or vice versa. This could lead to confusion and potential errors in communication.

Additionally, the use of prefixes is important for more complex molecules where multiple groups of the same type may be present on different positions of the carbon chain. For example, in a molecule with 5 methyl groups, using 5-methyl-pentane would clearly indicate that all five groups are present on the carbon chain, while using 1,2,3,4,5-pentamethyl-pentane may not be as clear.

In summary, the use of prefixes in organic nomenclature serves to accurately represent the structure of the molecule and avoid ambiguity. I hope this helps clarify your doubt. If you have any further questions, please don't hesitate to ask. Best of luck with your studies.