Molecular orbitals and stereochemistry - organic Flashcards
How are molecular orbitals formed
By atomic orbitals overlapping
What happens when two atomic orbitals combine
An anti bonding and bonding molecular orbital form.
How many electrons are in a molecular orbital
2
What happens when there is an end on overlap of atomic orbitals
A sigma bond is formed.
What happens when there is a side on overlap of atomic orbitals
A pi bond is formed
What happens when non polar covalent atomic orbitals overlap
The molecular orbital will be symmetrical around the mid point of the orbital.
What happens when polar covalent atomic orbitals overlap
The molecular orbital will be asymmetrical around the mid point of the orbital.
Rule of hybridisation
When different atomic orbitals a set of degenerate hybrid orbitals are formed.
Types of carbon hybridisation
sp3, sp2, sp
Sp3 hybridisation
Orbital structure
Where carbon goes from 1s2, 2s2, 2p2
To 1s2, sp3
sp3 molecular structure
Tetrahedral structure
Type of bond in sp3 hybridisation
Carbon single bonds
Sp2 hybridisation orbital structure
1s2, 2s2, 2p2
To 1s2, sp2 2p1
sp2 molecular structure
Trigonal planar
Type of bond in sp2
Carbon double bond
Types of orbital bond in sp3
7 sigma bonds
Types of orbital bond in sp2
5 sigma bonds and 1 pi bond
sp orbital structure
1s2, 2s2, 2p2
To 1s2 sp 2p2
Type of bond in sp hybridisation
Carbon triple bond
Types of orbital bonds in sp hybridisation
3 sigma + 2 pi
sp molecular structure
Linear
Alkynes homologous series
A group of hydrocarbons with a carbon to carbon triple bond
Alkynes general formula
CnH2n-2
What is a skeletal structure
Where in organic chemistry we draw compounds without carbons and assume there is the maximum number of hydrogens bonded on.
What does a benzene ring look like
It’s a hexagon with three lines inside for double bonds.
Or a hexagon with a circle inside it.
What does LUMO stand for
Lowest unoccupied molecular orbital
What type of molecular orbital is a LUMO
Anti bonding
What does HOMO stand for
Highest occupied molecular orbital
What type of molecular orbital is HOMO
Bonding molecular orbital
What type of light is absorbed by molecular orbitals without conjugated systems
UV light because the energy gap between the orbitals is so high
What is a conjugated system
Where an organic substance has a chain of repeating carbon single and double bonds, creating delocalised electrons across many different atoms bonding molecular orbital.
Conjugated system structure
Alternating carbon single and double bonds.
Rule of energy gap and conjugated system
The larger the number of atoms in the conjugated system the lower the energy gap between the HOMO and LUMO
Why are some organic substances coloured
Because they have long conjugated system which means that there is a lower energy gap between the HOMO and LUMO which means some wavelengths of light will be absorbed to promote electrons to higher energy levels, the complimentary colour will then be shown by the substance as this is the wavelengths of light reflected.
What is a chromophore
A group of atoms within a molecule responsible for absorbing visible light
Rule of chromophore and colour of compound
The compound will absorb the wavelengths of light which promote electrons to higher energy levels and all over wavelengths of light will be reflected, which shows the colour of the compound.
How do indicators work
The indicator goes from deionised to ionised which forms a large conjugated system and makes the indicator change colour.
Example of indicator
Phenolphthalein
Stereoisomers definition
Where a molecule has the same molecular and structural formula but different 3D arrangement in space.
Geometric isomers examples
Carbon to carbon double bonds and cyclo ring structure molecules.
Cis
When the two groups are on the same side.
Trans
Where the two groups are on different sides.
Rules of geometric isomerism
For geometric isomerism to occur there must be two different groups attached to the carbon atoms that make up the bond with restricted rotation.
How do geometric isomers differ
Influences chemical properties
Influences physical differences
Chemical properties example
Undergoes condensation or not
Physical differences
Difference in mp/ bp
Geometric isomers definition
Stereoisomers which have two different groups attached to carbon atoms that make up a bond with restricted rotation.
Optical isomers
Stereoisomers which are non super imposable mirror images of each other.
Enantiomers
Optical isomers (interchangeable)
Chiral centre
A carbon atom in an optical isomers where there are four different groups attached.
Enantiomers properties
In chiral environments they have different physical and chemical properties
In normal environments they have the same properties.
How to distinguish Enantiomers
They rotate polarised light in an equal and opposite way.
What is optically active
When Enantiomers rotate polarised light in an equal and opposite way.
Racemic mixture
Enantiomers of equal proportions which aren’t optically active.
