WTF!

[magnum]

Just did the STAV 08 chem exam n it had a question: draw the structural formula of methyl propan2ol! does that even exist?

[shinny]

I think that'd be like


Note: Sorry for the huge image, cbf cropping and resizing =P

[magnum]

i thought it was that, but isnt that 2-methyl propan2ol (cos the methyl group is attached to the 2nd Carbon)

[shinny]

I assume that no number is given for the methyl because 1-methyl doesn't work, and so it's assumed to be a 2 by default since it's the only one that works. 1-methyl would just make it butan-2-ol.

[TrueTears]

Yes the structure shinny drew was 2-methylpropan-2-ol

The methyl I *think* should be on the first carbon (I remember Dr Slade telling us even though the naming is 'wrong', you still draw what is said), which indeed, if you are following IUPAC rules it would not be named methylpropan-2-ol. But it does exist, just that the systematic naming is meant to be 2-butanol

[shinny]

Is that what normally happens in omissions of numbers? I can't remember =S I just assumed that was how it worked so yeh.

[TrueTears]

Is that what normally happens in omissions of numbers? I can't remember =S I just assumed that was how it worked so yeh.

yeah, if there is no numbers in front of the methyl, you assume it's on the first carbon. Same goes for chloro, bromo etc

[shinny]

Ah ok. Haven't touched chem in too long @_@ Then yeh, follow what TT has said I guess. Makes sense to me.

[cns1511]

I was under the same impression as shinny. I've seen in a few texts and on the net that methyl groups off propane molecules generally attach to the 2nd carbon since it is no longer propane went on the 1st carbon. Thus they have no need to specify that its on the 2nd carbon and you are meant to just assume that it is. That's what I thought anyway... (sorry if that made no sense I'm in the middle of a practice exam etc:P)

[Mao]

Is that what normally happens in omissions of numbers? I can't remember =S I just assumed that was how it worked so yeh.

yeah, if there is no numbers in front of the methyl, you assume it's on the first carbon. Same goes for chloro, bromo etc

The number is omitted where there can only be one isomer. This occurs very rarely, the few cases almost always have ethyl or propyl backbone. (Such as dimethylpropane, ethanol)

That is my understanding, and to my knowledge, methylpropane is accepted as the naming for 2-methylpropane.

[NE2000]

Is that what normally happens in omissions of numbers? I can't remember =S I just assumed that was how it worked so yeh.

yeah, if there is no numbers in front of the methyl, you assume it's on the first carbon. Same goes for chloro, bromo etc

Actually I disagree. I was told that methylpropane is sometimes used because there is no such thing as 1-methylpropane that is just butane, so methylpropane automatically means 2-methylpropane. In fact, once I was told not to write 2-methylpropane because there is only one possible isomer of methylpropane, so just write methylpropane. I have since dismissed that advice, coz this thread illustrates that all that does is create confusion.

[chem-nerd]

Is that what normally happens in omissions of numbers? I can't remember =S I just assumed that was how it worked so yeh.

yeah, if there is no numbers in front of the methyl, you assume it's on the first carbon. Same goes for chloro, bromo etc

The number is omitted where there can only be one isomer. This occurs very rarely, the few cases almost always have ethyl or propyl backbone. (Such as dimethylpropane, ethanol)

That is my understanding, and to my knowledge, methylpropane is accepted as the naming for 2-methylpropane.

yep, what Mao says is true

also, be careful with the chloro and bromo examples. make sure you specifically state 1-chloro if the chlorine is attached to the first carbon otherwise you will not get the marks

[magnum]

thanks everyone!

[chem-nerd]

from the 08 assessors report, for a similar question

Accepted names
   methylpropan–1–ol
   methyl–1–propanol
   2–methyl–1–propanol