# What is the difference between structural isomerism and geometric isomerism?

1. Oct 9, 2006

### lord12

What is the difference between structural isomerism and geometric isomerism??

Yea. The thread title explains it.

2. Oct 14, 2006

### FunkyDwarf

the answer, as well as the question, is in the title as well :) structural isomerisim is the same emperical formula but constructed differently. This is most apparent, obviously, in organic chemistry. So say you have 3 carbons and 6 hydrogens, you can arrange that in quite a few ways to make very different molecules but with the same emperical (not molecular) formula.

geometric isomerisim is where you have different isomers due to differences arrising from cis and trans arrangements of atoms.

3. Oct 15, 2006

### The Bob

Taking this a little further, 4 carbon atoms and 10 hydrogen atoms could be arranged to form simple Butane but it could also be 2-methylpropane. The two are structural isomers.

A geometric isomer could be one with a chiral carbon (correct me if I am wrong). The two are completely the same except, by rotation alone, they can never match up.

4. Oct 16, 2006

### FunkyDwarf

yeh thats optical isomerisim though which is a little different

5. Oct 16, 2006

### The Bob

Oh no...... of course you're right. How stupid of me. So sorry!

Cheers for the correction,

They differ in how they rotate polarized light (i.e. $$C_{2}H_{6}0$$