ISOMERS

ISOMERS : A topic which confuse maximum time and a question just spark in the mind "isomers" but how many can be made....
There are two ways to find the number of isomers and to draw the isomers of given hydrocarbon
1st : The Arthur Cayley method, the older way to give you approximation of the number of isomers can be made
2nd: Set of five rules which will never fail to get you to the correct isomers and its no. too.
but before illustrating it further lets see what are isomers actually?????
Name ISOMER is given by two Greek words:
ISOMERS = ISOS (EQUAL) + MEROS (PARTS)
ISOMERS are compounds with the same molecular formula but different structral formula, ISOMERS do not necessarily share similar properties, unless they have same functional group (-x,-oH etc)

The first and old way to find the no. of isomers :

In 1875, a mathematician named Arthur Cayley came up with a mathematical formula to calculate the number of isomers. Unfortunately, this--and all other non-computerized methods developed since then--was disproved.

You can, however, extrapolate the number of isomers of a given alkane from the "enumeration" sequence he created.

RULE for Arthur Cayley METHOD :

Consider all alkanes in the following terms:

CnH(2n+2). Keeping this in mind, determine "n" for your particular compound.
For example, if you have C5H12 (pentane), "n" = 5.

Consult Cayley's Sequence to 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 (Cayley's Sequence) :
1, 1, 1, 2, 3, 5, 9, 18, 35, 75, 159, 355, 802, 1858, 4347, 10359, 24894, 60523, 148284, 366319.
In the case of C5H12 (pentane) -which has five carbons (n=5) and therefore represented by the fifth integer of the sequence--the answer is three ( 3 ISOMERS).






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