Isomers!

[sam0001]

How many different isomers of Propanol can be formed?

[pi]

Two

1- Propanol and 2-Propanol

[thushan]

call it propan-1-ol and propan-2-ol. 1-propanol and 2-propanol are the old names. They were accepted previously, but i'm not sure whether they'd accept those this year.

[Hutchoo]

Hijacking this thread:

Is there some 'fullproof' method in terms of drawing isomers? For example, if I have a question that was asking to draw the Isomers of a molecule, let's call it xyz, is there some formula that shows how many possible isomers exist?
I understand if there's a 3 mark question and it asks to draw an isomer of xyz, you'd draw 3 isomers/name them, but in GENERAL, is there some method to know how many isomers exist?

Thanks.

[Kanon]

Hijacking this thread:

Is there some 'fullproof' method in terms of drawing isomers? For example, if I have a question that was asking to draw the Isomers of a molecule, let's call it xyz, is there some formula that shows how many possible isomers exist?
I understand if there's a 3 mark question and it asks to draw an isomer of xyz, you'd draw 3 isomers/name them, but in GENERAL, is there some method to know how many isomers exist?

Thanks.

I'm also very interested in this, I've been told that for Alkenes you can use factorials? 

[pi]

Not really, there are tricks, but not any definitive formulas.


For those who are interested (and bored), give this a look http://www.cs.uwaterloo.ca/journals/JIS/cayley.html

It isn't entirely accurate (ie. doesn't work all the time especially with larger compounds), but it's interesting

[AllAboutTheLGs]

I'm interested too because with most of the isomer questions (which are usually multiple choice questions may I add), I end up spending way more time than I should be spending on them by drawing them out, and trying to figure out if any are the same, confusing myself in the process.

[thushan]

I'm interested too because with most of the isomer questions (which are usually multiple choice questions may I add), I end up spending way more time than I should be spending on them by drawing them out, and trying to figure out if any are the same, confusing myself in the process.

This is how i teach my students to do it - and it's on my book as well:

1. Find number of double bonds from molecular formula.
2. Find all possible arrangements of carbons, oxygens, nitrogens (they all bond more than once) - don't forget to include double bonds
3. In each arrangement you did in step 2., draw all arrangements for all other non H atoms (Cl, F, I, Br)
4. Draw in the H atoms to complete the structures.

[charmanderp]

I've never seen a question at VCE level which requires you to draw isomers with double bonds though. Do you reckon it could crop up in an exam?

[thushan]

I've never seen a question at VCE level which requires you to draw isomers with double bonds though. Do you reckon it could crop up in an exam?

VCAA 2008, MCQ 16.

[charmanderp]

Touche. Derp derp. But what about questions where it's not mentioned that the molecule has a double bond?

[thushan]

None that I know of, but there's nothing ruling it out.

And the only reason they put "containing a double bond" is to stop people from drawing cyclopentane

[charmanderp]

Your cheek aside, touche again :p I never even think of drawing cyclic isomers :/