IIT JEE , AIEEE Forum - Chemistry , Organic Chemistry

rohitju

sir,

for calculating the no: of isomers, do v hav 2 write the structure of every isomer or is there a formula for calculating the no: of isomers by knowing the no: of c atoms?

thanx in advance!!!!!!!!

nishant

no. of isomers can be calculated by the formula 2^n where n is no. of chiral carbon atoms.

rohitju

but that is for no: of optical isomers. i want including stereoisomers and geometrical isomers

kiran

Hi

You can find the number of isomers by finding the DBE.

Double Bond Equivalents (D.B.E) or Index number .

It is a numerical value on the basis of which we can have an idea about the different type of equivalent structures we can have for a given formula. Mathematically

DBE = Summation [n (v-2)]/2 + 1

n= number of atoms

v = valency of the atom.

example. dbe of C₄H₆ is dbe = 4(4-2)+ 6(1-2) / 2 +1 = 2.

The index number is 2. The molecule may contain.

1) Two double bonds or one triple bond

2)one ring and one double bond

3) two rings.

The total isomers are acyclic isomers+ cyclic isomers.

Cheers.

rohitju

thanx a lot!!!!!

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