DF 9: What do the molecules look like? Flashcards
What is an isomer?
Molecules which have the same molecular formula but the atoms are arranged differently
What are structural isomers?
Structural isomers have the same molecular formula but different structural arrangement of atoms
What are stereoisomers?
The order of bonding is the same, but the arrangement of the atoms in space is different in each isomer
What do structural isomers have?
Different structural arrangements of atoms
How can organic compounds be arranged?
General formula Molecular formula Shortened structural formula Structural formula Skeletal formula
What is general formula?
A formula that can describe any member of a family of compounds (Example - the general formula for alcohols is CnH2n+1)
What is molecular formula?
The actual number of atoms of each element in a molecule (such as C4H10)
What is shortened structural formula?
Shows the atoms, carbon by carbon, with the attached hydrogens and functional groups (Such as CH3CH2CH2CH2CH3)
What is structural formula?
Shows how all the atoms are arranged and all the bonds between them
What is skeletal formula?
Shows the bonds of the carbon skeleton only, with any functional groups
What are the different types of structural isomers?
Chain Isomerism
Positional Isomerism
Functional Isomerism
Chain Isomerism
These isomers have similar chemical properties, but their physical properties like boiling point will be different because of the change in shape of the molecule
Positional Isomerism
They also have different physical properties and their chemical properties might be different too!
Functional Isomerism
They have very different physical and chemical properties
What is the relationship between an increase in the number of carbon atoms in the chain increases and the number of possible isomers?
As the number of carbon atoms increases the number of possible isomers increases
How can position isomerism occur?
When there is an atom, or group of atoms, substituted in a carbon chain or ring (these are called functional groups).
Position isomerism occurs when the functional group is situated in different positions in the molecules.
What are the two ways that atoms can be arranged differently in isomers.
The atoms are bonded together in a different order in each isomer (STRUCTURAL ISOMERS)
The order of bonding in the isomers is the same, but the arrangement of the atoms in space is different in each isomer (STEREOISOMERS)
What do CH4, C2H6 and C3H8 have in common (isomers)
There is only one possible isomer for them
Chain isomerism
The carbon skeleton can be arranged differently, for example a straight chain or a branched in different ways
Positional isomerism
The skeleton and the functional group could be the same, only with the functional group attached to a different carbon atom
Functional Isomerism
The same atoms can be arranged into different functional groups
What are the two types of stereoisomers?
Geometric isomers Optical isomers (Shapes)
Geometric isomers
They are also known as E/Z Isomers
Why do stereoisomers typically only apply to alkenes and not alkanes?
Alkanes dont contain any double bonds, single bonds allow atoms to rotate freely (Not stereoisomers)
Alkenes have at least one double bond, double bonds don’t allow the atoms to rotate so it is FIXED.
How can alkenes be stereoisomers if they have a fixed double bond?
Alkenes still contain single bonds in their molecules which means atoms can rotate and therefore the RESTRICTED rotation around the C-C double bonds is what causes E/Z isomerism.
What is an ‘E’ isomer?
‘E’ means opposite and corresponds to the term ‘trans’ which means both
What is a ‘Z’ isomer?
‘Z’ means together and corresponds to the term ‘cis’
How do the above rules of ‘E’ and ‘Z’ isomerism work?
This rule works when either of the two groups on either end of the double bond are the same or there is a hydrogen on both carbons.
What is E/Z Isomerism all about?
Having 2 Hydrogens singly bonded to both carbon atoms
What is trans/cis isomerism all about?
trans/cis isomerism can be used when you don’t have two hydrogens
Naming alcohols
Find the longest carbon chain (Name it)
Determine the position of the alcohol group (OH) by counting the carbons to give the lowest number
Add ‘ol’ to the end of the name
