Isomers Flashcards
When does isomerism occur?
When compounds have the same molecular formula but different structural formulas
How many types of isomers are there?
Two
What are the two types of isomers?
Structural isomers
Geometric isomers
When do structural isomers arise?
When compounds have the same number and types of atoms, but are arranged in different ways
How many types of structural isomers are there and what are they?
Three
Chain isomers
Positional isomers
Functional group isomers
How do you know it’s a chain isomer?
The compounds have different parent chains
Eg:
Pentane → 2 methylbutane or 2,2 dimethylpropane
How do you know it’s a positional isomer?
The molecules have a functional group in different positions on the parent chain
Eg:
Propan - 1 - ol and propan - 2 - ol
How do you know it’s a functional group isomer?
The molecules belong to different homologous series
Eg:
Ethane → ethanol and methoxymethane
What are the conditions for geometric isomers to be able to form?
- There must be a double bond (must be an alkene)
- The alkene must have different atoms that are attached to the double bond
Why must there be a double bond for geometric isomers?
The double bonds are fixed and doesn’t allow for rotation. This allows different arrangements of the atoms bonded to the carbons in the double bond. The different arrangements are called the geometric isomers.
Why can’t geometric isomers form from alkanes?
Alkanes have single bonds that can freely rotate
What are the two types of geometric isomers?
Cis isomers
Trans isomers
What are cis isomers?
Geometric isomers where the atoms are adjacent to each other across the double bond (on the same side)
What are trans isomers?
Geometric isomers where the atoms are on opposite sides of the double bond
When do cis/trans isomers apply?
When both halogens are on the carbon atoms that make the double bond
