Week 5 Module 2 Flashcards
Refer to notes <3
What is the issue with only considering the overlap of atomic orbitals?
It is not enough to describe the shape of some molecules.
If we think about the shape of the p-orbitals and overlap, it doesn’t really explain bond angles or why bonds are equal.
What is the theory of Hybridisation?
S and P orbitals hybridise.
In sp3, the shape is 75% p character and 25% s character. - there would be more electron density on one side.
What would happen in methane using Hybridisation? Refer to notes and lecture content
If we have 4 things, they will push away and get 103 degree speration where carbon is single bonded.
Refer to notes about Ethene.
(and Ethine)
3sp2 orbitals per carbon, 1 overlaps with other carbon, the other two with the hydrogen. These make sigma bonds.
Still has unhybridised p orbital with dumbbell shape around the carbon. pi bond gives ethene the double bond.
How will you be able to identify C, N, O hybridisation?
By the types/number of bonds made. O and N have lone pairs that sit inside an hybridised orbital.
If the number of sets of electron pairs was 2, what would be the electron geometry, hybridisation, number of hybrid orbitals, and number of unused p-orbitals be?
linear, sp, 2, and 2.
If the number of sets of electron pairs was 3, what would be the electron geometry, hybridisation, number of hybrid orbitals, and number of unused p-orbitals be?
Trigonal planar, sp^2, 3, and 1.
If the number of sets of electron pairs was 4, what would be the electron geometry, hybridisation, number of hybrid orbitals, and number of unused p-orbitals be?
Tetrahedral, sp^3, 4, and 0.
For all types, lone pairs need to be taken into account.
What does NMR spectroscopy stand for?
Nuclear magnetic resonance.
What does NMR spectroscopy do?
Helps determine number, types, and connections of atoms. Only works with nuclei tat have a nuclear spin - needs an odd mass or atomic number.
Helps identify products of reactions, etc. used in medicine.
What happens in an NMR machine?
The sample is put in a solution and into the machine which applies a magnetic field. A lower energy state is where they are with the magnetic field (some mau be against). Radiation is then applied, flipping those in a lower energy state so they are against the field. (the gap between states is quite small). Out of the machine, we get data that is passed through a computer to do calculations and results in a spectra. One giant line is a signal - tells us the spectra for this molecule.
Why is there a magnetic field applied in an NMR machine?
Because when there is no field, they spin in any direction. The MF makes them line up either pointing with or against the field.
What is higher in energy, when the spins are with the magnetic field or against?
Higher when the orientation is against.
What does radiation do in the NMR machine?
Lower energies absorb the energy and move to a higher energy state.
What are the 3 things we look at in a n NMR spectrum?
- Integration
- Multiplicity
- Chemical Shift
With this info, we can build the structure of the molecule. Especially with MR, DBE, and IR info.
What is integration?
The area under the peak in the signal - the number of H atoms in the environment creating the signal.
What is Multiplicity?
Can note it is not an individual peak that makes up 1 signal. - Number of adjacent H.
What is the Chemical Shift?
The scale across the bottom. What type of environment H is in.
What is the relative area of integration?
The relative number of H. Can also use the difference between lines (like a ratio).
Remember that single bonds have movement.
eg. 2H under 1 signal. They are chemically equivalent, likely bonded to the same carbon - Would be a CH2 group.
What is the problem with a multiplet?
Messy. Can’t get any info but integration.
How does the lines in multiplicity work?
The line are based on the number of adjacent H.
What does signal multiplicity equal?
Number of adjacent spins + 1.
What does it mean if something is chemically inequivalent?
They are bonded to two different things. - refer to page 36 for examples.
What happens to multiplicity if there is a Hydrogen bonded to something like an O?
It blocks the coupling between adjacent hydrogens - creates a broad signal that doesnt appear to have multiplicity.
- A broad singlet. Can assume it is bonded to an oxygen. Can’t get multiplicity.
Bonded to N and O still get counted.
