OK, so isomers are molecules with the same chemical formula, have a different chemical structure. There are different types of isomers, including structural isomers and stereoisomers.
Structural isomers - these are molecules which have the same molecular formula but have a different structural/displayed formula. There are 3 types:
- Chain isomers: this is where the
carbon skeleton can be arranged differently. So butane and methylpropane are chain isomers as they both have the same chemical formula (C
4H
10) but the difference between the two is that one of the CH
3's in butane is taken out and placed on the middle carbon, so the carbon skeleton has been rearranged.
- Positional isomers: this is where a
functional group has been
placed on a
different carbon atom. 1-chloropropane and 2-chloropropane are examples of this as the chlorine atom (the main functional group - halides) has been placed on a different carbon atom, but they have the same chemical formula.
- Functional group isomers: this is where the atoms in the molecules have been
arranged to form a different functional group, but they still have the same chemical formula. So hex-1-ene and cyclohexane are examples of this as they both have the same chemical formula (C
6H
12) but the first one's an alkene and the second's an alkane (different functional groups).
Stereoisomers - there are E/Z (cis/trans) isomers and optical isomers (enantiomers), but I'll only go through E/Z
. Stereoisomers are molecules which have the same structural formula but have a different arrangement in space.
E/Z: C=C bonds have a lack of rotation around the double bonds. When the each of the carbons in the double bond have two
different atoms or groups attached to them, you get an E and a Z isomer. You don't need to know about deciding priorities, but if the two higher priority groups are on the same side of the C=C double bond, then the molecule's the Z isomer, if they're on opposite sides, it's the E isomer, E for entgegen (opposite), Z for zusammen (together), knowing a tiny bit of German helped me with this
This may not make sense until you look at diagrams or build models, it hard to put this into words. Maybe read this
http://www.chemguide.co.uk/basicorg/isomerism/geometric.html#top until the red Note and then read this
http://www.chemguide.co.uk/basicorg/isomerism/ez.html#top sorry, I can't explain E/Z properly using words, I'd need a whiteboard
Hope this helped! Others can correct this if need be