Swarley's Chem Questions :)

[Zien]

I've always known it as 2-methylbutane. But now I'm thinking about it, I'm just wondering if it's allowable to exclude the number in front of 2-methylbutane because methylbutane implies that it's attached to the 2nd carbon atom. It can't be 3-methylbutane since you always number from the end with the nearest side chain (so it would be 2-methylbutane) and, 1-methylbutane or 4-methylbutane would just be pentane. Cis and tran doesn't apply here either. Hmm. Can anyone clarify?

In any case, I think your sheet meant 2-methylbutane. ^^

[luken93]

Yeah. Sorry for tthe confusion. The question wants you to draw the structural formula for methylbutane. But the answer has the structural formula for 2-methylbutane.
So what im asking is methlybutane and 2-methylbutane are different things?

I'd say it's a typo

They aren't the same things, just like Propanol = Propan-1-ol, but =/= Propan-2-ol

[Greatness]

There are quite a few errors between quetsoins and answers from the heinemann textbook....

-Zien, i dont understand how methylbutane implies that it is 2-methylbutane :s

[Zien]

But that example isn't applicable here though. Whereas Propan-1-ol can be oxidised into its corresponding aldehyde and then its corresponding carboxylic acid , propan-2-ol can only be oxidised into its corresponding ketone. They're in totally different 'environments.' 2-methylbutane and 3-methylbutane have the same 'environment', only a naming rule that we start counting from the end with the nearest chain disallows 3-methylbutane as a name. They're the same.

.. at least that's what I'm thinking?

[luken93]

There are quite a few errors between quetsoins and answers from the heinemann textbook....

-Zien, i dont understand how methylbutane implies that it is 2-methylbutane :s

Zien is saying that the only way a methyl butane can exist is if it's attached to the 2-C, as attached to 1 or 4 would be Pentane, and 3 would be the same as 2-C

I'd still say it's a typo though, I'm fairly sure they don't "assume" these things hahaha

[Greatness]

Ohhh ok
Next question: Which is notation is more correct  when youre writing chloropropane or 1-chloropropane. I know that it doesnt really matter but ive heard that having the 1 there is safer.

Also if you are given a structural formula how do you know if there is branching? Is it if there is just a CH? Cos i get confused with all the brackets and stuff in those crazy molecules >>

[Water]

Lol a) Yeh, I always write 1-chloropropane. You don't want a what bitch examiner or teacher marking you down, for not having it, so better prevention than cure.



b) I think its a matter of practise


CH3 (CH2)3 CHOH (CH2)2 CH3

From there, we'd know that there would be a branching in the CH sector because of the OH, then we'd just count from the shortest carbon chain.  

In other cases you'd have

CH3CHCH3(CH2)5CH3

which would be a methyl branching out, indicated by the CH3 adjacent to CH and CH2.

I hope your doing heinemen, page 142, on question 11, they have exercises that help with the branching.

[Greatness]

Alright cool! Yeah i was doing qn 11 took me some time tho

[scocliffe09]

Ohhh ok
Next question: Which is notation is more correct  when youre writing chloropropane or 1-chloropropane. I know that it doesnt really matter but ive heard that having the 1 there is safer.

Also if you are given a structural formula how do you know if there is branching? Is it if there is just a CH? Cos i get confused with all the brackets and stuff in those crazy molecules >>

There are some molecules where the two types of notation are less vital [ but I would still be safe and write the number] (e.g. 2-chloro-2-methylbutane vs 2-chloromethylbutane because the methyl group has to be on carbon 2.) BUT with the example you gave (chloropropane) there are different types of chloropropane so you HAVE to write 1-chloropropane or 2-chloropropane, because chloropropane is ambiguous.

And yes, the most helpful thing to remember is that each C atom usually has a total of 4 bonds - so if it only has one H atom bonded to it, then its 3 other bonds are probably to another C or a heteroatom/s.

[Mao]

Zien and scocliffe09 are correct. the '2' in 2-methylbutane is redundant. Naming only needs to go so far until there are no ambiguities in the structure. methylpropane is also fine. methylpentane is not okay (since there is 2-methylpentane and 3-methylpentane), however ethylpentane is okay.

Substituted functional groups generally always require numbering. This is since they can substitute at any carbon, hence for anything larger than 2 carbons they will always require a number.

Not having a number does not imply substitution at position 1.

[Greatness]

Thanks Mao. Looks like ill have to make writing the carbon no.s a habit!

[thushan]

That reminds me, I was wondering, unless the question specifically asks to 'show all bonds' will they accept line drawings for organic molecules?

[Mao]

That reminds me, I was wondering, unless the question specifically asks to 'show all bonds' will they accept line drawings for organic molecules?

I would assume so. It is after all what every chemist uses.

[pi]

That reminds me, I was wondering, unless the question specifically asks to 'show all bonds' will they accept line drawings for organic molecules?

My teacher said to avoid it

(by line drawing, I assume you mean just drawing the skeleton of the molecule, ie. no carbons or hydrogens shown)

[jasoN-]

i think they'd allow it o.o, it looks much cleaner (of course unless they specify to show all bonds)