Isomers (1 Viewer)

[BIGTYMA]

Is there an easier way to find out how many isomers a substance has other than drawing each possible isomer?

use C3.H6.Cl2 as an example.

thanks.

 

[ssglain]

What level of maths do you do? It probably won't make sense when I say you can arrange the chlorine atoms using permutation unless you do at least MX1.

If you have to maths to help you, try it for yourself, although I won't guarantee that it to be any easier than drawing out all the different isomers.

As a hint, consider two cases:
Case 1: Each Cl atom goes to a different C atom.
Case 2: Two Cl atoms stick together and go to the same C atom.

Also keep in mind that because your haloalkane can be flipped around and read the same from the other end, you have to take care not to over count.

 

[chousta]

yea pretty much...

or u can do wat ssglain said but remeber that basically the only thing moving around is the chlorine.


so we can ignore everythin else
and consider the patterns where the(1st chlorine postion, second cholrine position) where order doesnt matter


ie.
(1,1) (1,2) (1,3) (2,2)

thus, answer is 4

TYPO:written early in the morning

 

[wrxsti]

What level of maths do you do? It probably won't make sense when I say you can arrange the chlorine atoms using permutation unless you do at least MX1.

If you have to maths to help you, try it for yourself, although I won't guarantee that it to be any easier than drawing out all the different isomers.

As a hint, consider two cases:
Case 1: Each Cl atom goes to a different C atom.
Case 2: Two Cl atoms stick together and go to the same C atom.

Also keep in mind that because your haloalkane can be flipped around and read the same from the other end, you have to take care not to over count.

Omg, permutations :S
could you explain how exactly this would work for this question (like the permutation)

Order is important so its a perm?
i hate isomers. ... hoping this permutations can make it easier

 

[MrZ]

There is but your mathematical skills need to be good in determining the number of permutations possible: Eg simple hydrocarbons such as methane, ethane and propane obviously dont have isomers, but butane has 2, pentane 3, hexane 6...and C20H42 would have 366 319 isomers! If other atoms are present, then the permutations increase further. Think of what a typical HSC question may ask, the exam committee would probably restrict it to a maximum of 5 carbons in the chain or associate one isomeral structural formula to another. Your question of isomers of dichloro propane would have a maximum of 3: 1,1-dichloro propane, 1,2-dichloro propane and 1,3-dichloro propane. Sorry "chousta" but you are incorrect as 2,3-dichloropropane is a redundant term for 1,2-dichloro propane. So there are only 3 for this example. It is best you quickly draw them out as you have about 1.8 minutes per mark to determine the answer, but for longer chains note any cyclic or double bond possibilties that may exist. Mr Z

 

[chousta]

buddddddddddy.......im not wrong.....

because::
a. my logic is correct
b.thats the correct answer from the solutions.


so "MrZ" it seems that ur answer is "redundant"

 

[wrxsti]

lol chousta...

i think i might stick to original method of just drawing em up???????

 

[brenton1987]

buddddddddddy.......im not wrong.....
because::
a. my logic is correct
b.thats the correct answer from the solutions.
so "MrZ" it seems that ur answer is "redundant"

You are wrong because:
a. your logic is flawed.
b. the 'correct' answer is wrong.

Molecules 2 and 4 are clearly the same and they represent 1,2 and '2,3' dichloropropane.

 

[MrZ]

Right of Reply...
There's also 2,2-dichloro propane as well. This now gives a total of 4:

1,1-dichloro propane
1,2-dichloro propane
1,3-dichloro propane
2,2-dichloro propane

Perhaps this is what the answer meant but 2,3-dichloro propane, as well as 3,3- dichloro propane, are still incorrect.

Mr Z.

 

[chousta]

You are wrong because:
a. your logic is flawed.
b. the 'correct' answer is wrong.

Molecules 2 and 4 are clearly the same and they represent 1,2 and '2,3' dichloropropane.

my logic wasnt flawed it was merly a typo

there is obviously 4 different isomers, brendon1987 maybe u should just stick to ur time frame.....2005 was a long time ago....

Explanation:

Draw the carbon chain C–C–C then see where you can place the two Cl atoms: 1,1-, 1,2-, 1,3- and 2,2-. Be careful to recognise that 2,3- is the same as 1,2- and that 3,3- is 1,1- (that's where the 5 and 6 answers come from). Note that both Cls can be on the one C atom – otherwise you might choose answer A.

 

[brenton1987]

there is obviously 4 different isomers, brendon1987 maybe u should just stick to ur time frame.....2005 was a long time ago....

I know that theres 4 isomers. I was just showing that your original answer was wrong.

 

[nadz001]

You are wrong because:
a. your logic is flawed.
b. the 'correct' answer is wrong.

Molecules 2 and 4 are clearly the same and they represent 1,2 and '2,3' dichloropropane.

hey doesnt molecule 2 n 4 present the same molecule so isnt called 1,2dichloropropane, because u always count the nearst carbon

 

[lunavixen]

i just draw them, my maths is okay, but it's a chem exam, not maths, we got told to only use maths in chem when it's needed