Double Bonds, Configurations And Conformations Flashcards
What are the two types of molecular bonding orbital
Pi
Sigma
What is a sigma bond
Covalent bond formed from sharing a pair of electrons in a sigma orbital
What is a pi bond
Covalent bond formed from sharing a pair of electrons in a pi orbital
Draw the distribution of electrons for sp2 hybridised carbon atom
Trigonal planar shape
2p2 hybridised (since it wants to form 3 bonds)
The 2pz orbital doesn’t combine (its unhybridised)
What does hybridisation of orbitals do
It takes all of the electron density of the carbon atom and divides it up equally into hybridised molecular orbitals
Draw the energy level diagram for the molecular orbitals in ethene
Draw a diagram of the pi and sigma bond in ethene
What is bond length determined by
The more electrons there are in a bond= two nuclei can become closer = shorter bond length
Why can’t rotation occur around a c=c bond
This is because the pi bond isn’t cylindrically symmetrical
How do cis/trans isomers form (aka geometric isomerism)
Change in configuration
The groups attached to one carbon can swap places- to do this the pi bond would have to break
Cis= same groups are on the same side
Trans= same groups are on opposite sides
What is a node
A point where the probability of finding an electron is zero
What arrangement of nodes can there be for benzene
Show the electrons in the bonding and anti bonding orbitals of benzene
What are heterocyclic aromatic systems
They contain nitrogen or oxygen instead of carbon in a ring
Show the distribution of electrons for pyrimidine
Show the distribution of electrons in pyrrole
Nitrogen will contribute 2 electrons so there 6 electrons in the bonding orbital
How would atoms in a molecule share a greater number of electrons
What are single, double and triple bonds made up of in terms of pi and sigma bonds
What are conjugated bonds
How are the electrons in a molecule of benzene arranged
Each carbon has 3 sigma bonds and one valence electron (which isn’t directly involved in bonding) which occupies a p atomic orbital
The p orbitals on each of the 6 carbon atoms in the ring overlap to form a single uninterrupted pi orbital (which form 2 ‘donuts’ above and below the plane of the carbon ring- these e- are free to move anywhere that forms the lowest energy in the pi orbital
What is a delocalised system
A delocalized system in chemistry refers to a situation where electrons are not confined to a single atom or a single covalent bond. Instead, these electrons are spread out or “delocalized” over several atoms
How does a conjugated system arise
What do atomic orbitals represent
Atomic orbitals represent electron wave functions
Orbital overlap involves combination of these wave functions
How does the bonding in hydrogen work
H atom has one electron in 1s orbital
1s orbitals of two H atoms overlap to form sigma orbital
Both electrons from each hydrogen atom reside here
Why does a bonding and anti bonding orbital form
The number of orbitals have to stay the same
So since 2 orbitals are overlapping to form a molecular orbital, 2 hybridised orbitals would form -> a bonding orbital and anti bonding orbital
How can electrons jump from the bonding orbital to the anti bonding orbital
Electrons can jump from a bonding orbital to an anti-bonding orbital through the absorption of energy. This process typically occurs when the molecule absorbs a photon of light (electromagnetic radiation) with energy equal to the energy gap between the bonding and anti-bonding orbitals.
How do molecular orbitals allow an atom to form bonds with other atoms to form a molecule
When atomic orbitals are hybridised to form hybridised molecular orbitals they would be on the same energy level
Each orbital would have one electron residing in it
This leaves room for another electron to be provided by another atom to form a bond
The number of hybridised orbitals formed would depend on the number of bonds that need to be formed
E.g methane would have 4 hybridised orbitals and would undergo sp3 hybridisation to form 4 bonds with 4 hydrogen atoms
Why is there a 2p orbital left unhybridised in carbon when it forms ethene
Sp2 hybridisation-> occurs to form double bonds
The orbital left unhybridised will be used to form a pi bond
Also because to form ethene, only 3 molecular orbitals are needed to form 3 bonds with 3 other atoms
How are orbital diagrams for a molecule drawn
What’s the difference between a sigma orbital and a hybridised molecular orbital
A sigma orbital is a molecular orbital formed by the head-on overlap of atomic orbitals along the internuclear axis, while a hybridized molecular orbital is formed by the combination of atomic orbitals on the same atom to create new orbitals that are used to form sigma bonds and accommodate lone pairs in a molecule
