3:11 organic synthesis

What kind of synthesis routes do Christy try and design

Routes that use non-hazardous starting materials to limit the potential for accidents and environmental damage. They also want to reduce waste so they want high atom economies and high percentage yield because they convert more of the starting materials into useful products. Waste can also be reduced by designing synthesis routes that have a few steps as possible.

Avoid using solvents wherever possible is a way of reducing hazards and waste as solvents are flammable and toxic so carry safety risks. If the solvent has to de disposed of after the reaction is complete then it can create a lot of waste

Two types of NMR (nuclear magnetic resonance)

What atoms spin

13CNMR which treks you how carbon atoms are arranged and 1HNMR which tells you about how the H atoms in a molecule are arranged

Atoms with an off number or nucleons - protons and neutrons - in its nucleus has a nuclear spin which causes it to have a weak magnetic field. NMR looks how this magnetic field reacts in a large external magnetic field. Therefore Hydrogen nuclei have a spin, and 1% of carbon atoms are 13C so they also have a spin

What happens when an external magnetic field applied and how does this relate to NMR being measured

Normally the nuclei spin in random directions so their magnetic fields cancel out but when a strong external magnetic field is applied the nuclei will all align either with the field or opposed to it. The nuclei aligned with the field will have a slightly lower energy level than the opposed nuclei

Radio waves of the right frequency can give the nuclei that are aligned with the external magnetic field enough energy to flip up to the higher energy level. The nuclei opposed to the external field can emit radio waves and flip down to the lower energy level. To start with here are more nuclei aligned with the external field so there will be an overall absorption of energy and NMR measures this

For 2 atoms to be in the same environment, they…..

Must be joined to exactly the same things (not just directly) as a nucleus can be partly shielded fro the effects of an external magnetic field by its surrounding electrons

What is chemical shift

What is the standard substance

What units is chemical shift measured in

NMR measures the difference between different nuclei and the energy they absorb at different frequencies. It’s compared to a standard substance and the difference is called chemical shift.

Tetramehtylsilane (TMS) Si(CH3)4 It has 12 hydrogen atoms all in the same environments so produces a single absorption peak and its well away form most other peaks. Its also used because its inert and doesn’t react with the sample, its non-toxic and volatile

Parts per million relative to TMS, so a single peak produced by TMS has a chemical shift of 0

What does number f peaks in 13CNMR tell you

How to work out number of carbon environments with an aromatic ring

What does the data table tel you

How many different carbon environments there is.

If the molecule is an aromatic ring, you will have to look for lines of symmetry to work out how many carbon environments there are

Chemical shift of certain carbon environments relative to TMS

What do the peaks in 1H NMR tell you

What does the tiny peak at the right mean

Each peak is due to one or more H in a particular environment. The numbear of peaks on a 1HNMR spectrum tells you the ratio of the areas under the peaks. This realtime area tells you the relative number of H atoms in each environment, they can be ratios as well as well as whole numbers.

Peak due to TMS set at 0

What does it means if the peaks are split into smaller peaks

It translates to the number of hydrogens on the neighbouring carbon(s), plus one. N+1 rule.

Singlet = 0 H on adjacent C

Doublet = 1H on adjacent C etc….

What is integration traces in 1H NMR

When the increases in height is proportional to the areas under each peak. You can use a ruler to measure the height of each vertical part and compare. The are under earth is equal to the ratio

If a sample has to be dissolved for 1H NMR what solvent is used

Solvent that is H-free as these would show on spectrum and confuse things. Deuterated solvents are used. These solvents have ben replaces by Deuterieum (D / 2H) It is an isotope of H)it has an even number of nucleons so it doesn’t have a spin and so doesn’t create a magnetic field.

CCl4 can also be used as it doesn’t contain any 1H either

Basic principles of chromatography

Mobile phase moves through the stationary phase

Distal between each substance moves up the plat sends on its solubility in the mobile phase and its retention int he stationary phase

Components that are more soluble in the mobile phase will travel further up the plate

How are colourless chemicals revealed during chromatography

Many plats have fluorescent dye added to the silica or alumina layer so it glows when Uv light shines on it. Use a UV lamp and draw circle around the dark patches

Expose the chromatograph to iodine vapour (leaving the plate in a sleazed jar with iodine crystals) Iodine vapour is a locating agent so it will stick to the plate an show up as brown / purple spots

What can alter an Rf value form the standard Rf values in a data book

TLC plate, solvent, temp will give different Rf values

If you so suspect a mixture contains a certain element then put a spot of chlorophyll on the baseline of a same plate and run them both at the same time.

How does column chromatography work

Mostly used for purifying an organic product.

Involves a glass plume with a slurry of absorbent material such aluminium oxide, coated with water = stationary phase. The mixture is added from top and allowed to drain down, a solvent is then run slowly and continuously through the column = mobile phase. As the mixture moves, its components seperate out to how soluble they are in the mobile phase and how strongly they are adsorbed onto the stationary phase (retention) Each different opponent will sped some time adsorbed onto the stationary phase and some time dissolved in the mobile phase. The more soluble each component is n the mobile Ashe the quicker it passes through

What is gas chromatography and when is used

Use for gas chromatography

To separate mixtures of volatile liquids.(ones that tun to gases easily)

stationary phase is a solid or a solid coated by a viscous liquid such as on oil and packed into a long tube which is coiled to save space and built into an oven. The mobile phase is an unreactive carrier gas such as N. Each component takes diff amount of time from being injected into the tube to being recorded at the other end = retention time.

Each separate substance will have a unique retention time so you can use this time to identify the component a( you have to run a known sample under same conditions for comparison) At the end is a detector and recorder that generates a chromatograph and the area under each peak is relative to the amount of component that’s present in each mixture.

Can be used to fine level of alcohol in blood or urine and is accurate enough to be used in court

What is GC-MS

Gas chromatography-mass spectrometry combines benefits of gas chromatography and mass spectrometry to make a super analysis tool. The sample is separated using GC and its then fed into a mass spectrometer. the spectrometer produces a mass spectrum for each component, which an be used to identify each one and show what the original sample consisted of. Computers can be used to match the spectrum to a database, so the whole process can be automated.