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Structural Isomers

How can I work out the possiblities? Is there some sort of formula.

How would I go about working out how different structural isomers can be formed when chlorine reacts with dodecane to form C12H25Cl ??

As this question is 1 mark, I'm thinking there must be a quick way of doing it, but I can't see how.

Thanks for your help.
Reply 1
Avatar for cobra
cobra
14
Matt_2K
How can I work out the possiblities? Is there some sort of formula.

How would I go about working out how different structural isomers can be formed when chlorine reacts with dodecane to form C12H25Cl ??

As this question is 1 mark, I'm thinking there must be a quick way of doing it, but I can't see how.

Thanks for your help.

if you just think about a straight chain alkane it can add in a number of places = number of carbons/2 as once it goes past the middle it's the same as a previous isomer, draw a few and see
Reply 2
Avatar for CalculusMan
CalculusMan
OP
10
So C12H25Cl has 6 structural isomers?
Reply 3
Avatar for Morbo
Morbo
17
7, i'd guess - it can go on the end as well
Reply 4
Avatar for Fly.
Fly.
1
cobra
if you just think about a straight chain alkane it can add in a number of places = number of carbons/2 as once it goes past the middle it's the same as a previous isomer, draw a few and see



This is only applicable for alkanes containing an even number of carbons.
Reply 5
Avatar for Stranded
Stranded
11
w w w . c h e m g u i d e . c o . u k might help
there is no formula for working out the number of possible isomers for a specific molecular formula
nonane has 35 and decane has 75 structural isomers. These numbers spiral out of control so that eicosane with 20 carbons has 366,319 isomers.
I don't have information on the actual of number for dodecane but it will be in the hundreds.
All of this is without considering the additional isomers when a chlorine atom (or chlorine atoms) is/are to be located on the molecule.
The only possible answer is that you are being asked for the number of monochloro isomers on the straight chain n-dodecane in which case there are 6 as the molecule is symmetrical and
carbon no. 1 = carbon no 12,
carbon no. 2 = carbon no 11,
carbon no. 3 = carbon no. 10,
carbon no. 4 = carbon no. 9,
carbon no. 5 = carbon no. 8,
carbon no. 6 = carbon no. 7.
Arthur Caley was a mathmatician who tried to derive a formula for such a question ,while his work was disproved by modern computors, it is still useful and mostly correct from what I can gather.


first determine how many isomers this "n" alkane has. For any alkane CnH(n+2), where "n" is any integer between 1 and 20, the following sequence represents the number of isomers possible: 1, 1, 1, 2, 3, 5, 9, 18, 35, 75, 159, 355, 802, 1858, 4347, 10359, 24894, 60523, 148284, 366319. In the case of pentane--which has five carbons and therefore represented by the fifth integer of the sequence--the answer is three.
The answer to your exam question is just 6, but as Charco points out this is far from all the structural isomers of chlorododecane!

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