super simple Q: naming (1 Viewer)

[mojako]

we have a heptane
it also has a methyl branch
it also has bromine in the heptane chain

which part gets the lower number, methyl or bromine?

 

[Tommy_Lamp]

you mean the lowest carbon number?

i do them in alphabetical order usually, so the bromine first

 

[mervvyn]

i was taught to do it to get the lowest possible sum when you add all the carbon numbers, if that makes sense. I don't think it's that important though, as long as the numbers are correct relative to each other...

 

[Xayma]

Im pretty sure it is the one with the lowest locant.

mervvyn its not the lowest sum, its the first difference, and the one with the lower number at first difference takes precedence (although off the top of my head I cant think of an example where they differ, yes I can 2,7,8 takes precedence over 3, 4, 9)

 

[mojako]

so neither alkyl nor halogen atom gets priority in the number?

 

[Xayma]

so neither alkyl nor halogen atom gets priority in the number?

As far as I can tell from the IUPAC rules, no.

 

[Lexicographer]

Take a look at my attached image.

I'm assuming you understand the structural representation of course, and that you have to number the carbons to give the lowest numbers to the substituents - in this case the carbon branch (methyl group) takes priority over the halogen. When naming, you should place the substituents in alphabetical order (even if this doesn't put them in numerical order).

 

[mojako]

I think your diagram isnt a very good example.
methyl will get 4 no matter how you name it...

 

[Tommy_Lamp]

Just do it in alphabetical order, for example:
in your example, you have heptane with a methyl branch and bromine. To make it simple, lets say that they are on opposite end of the carbon-chain, i.e. one of them will be 1, the other will be 7. so that means you would write it as follows:
1-Bromo-7-Methylheptane

 

[mojako]

probably its best to worry about this at university
HSC wont care

 

[Tommy_Lamp]

lol yeah probably, but its good to have a set method of writing them out, it helps for Q's

 

[mojako]

just going over my folder today...
my teacher says that halogen gets priority over the alkyl (provided the total numbers.. or sum of locants.. are the same of course)
but he also says that the most electronegative halogen gets priority
I mean, his source comes from one of those people or system.. see
http://www.boredofstudies.org/community/showthread.php?t=35442

probably for the HSC you can just number alphabetically.

 

[~*HSC 4 life*~]

hsc does care, ive seen trial q's on naming!

 

[mojako]

this particular type of naming?

 

[~*HSC 4 life*~]

this particular type of naming?

why not? i think i have...i was talking about your first q, but anyway whatever

 

[Lexicographer]

Trial questions aren't so important. What you need to look out for are the actual past HSC papers - THEY are the ones that reveal what the examiners want!