Organic Synthesis And Analysis Flashcards
What compound is used as a reference for NMR (draw it)
Tetramethylsilane
Why is TMS used as a reference (3)
It produces a single intense peak (all hydrogen and carbon atoms are equivalent)
It is non toxic and chemically inert
It is upfield (to the right) from nearly all peaks produced by hydrogen/ carbon atoms
What is 13C nmr used for
To determine the number of carbon atoms in different environments
What is the relationship of chemical shift values and the position of carbon atoms
The closer a c atom is to an electronegative atom the higher its chemical shift value
What is the integration ratio
The area under the peaks on a 1H nmr spectrum are proportional to the number of hydrogen atoms in a specific environment
What is the n+1 rule
The number of peaks in one cluster is one more than the number of hydrogens attached to the neighbouring carbon
What is the name of something with 1,2,3 or 4 peaks
Singlet
Doublet
Triplet
Quartet
What is the pattern of integration ratios
Binomial expansion
(1+x)^n where n us number of neighbouring hydrogens
What does an integration of 3 or 9 usually represent
2 or 3 methyl groups in same environment
What is the ruling in symmetrical molecules
Equivalent hydrogen atoms have no effect on each other so there is no splitting
What solvents are used for 1H nmr
CCl4
CDCl3
CD2Cl2
D2O
Deterioum is used instead of hydrogen so that the hydrogen in sample isn’t confused with the one in the solvent
Refer to photo
What is chromatography
A series of analytical techniques used to separate mixtures of compounds
What is the stationary phase (3)
Phase that doesn’t move
It can be solid or liquid
The compounds in mixture adsorb to it
What is the mobile phase
The phase that moves
Based on solubility the compounds move faster
Can be liquid or gas
What is RF in TLC
Distance travelled by spot / distance travelled by solvent front
What is true for rf values
Always less than 1
What is the stationary phase in tlc
A piece of plastic coated with a thin layer of a solid like silica it alumina
What is the mobile phase in TlC
A liquid solvent that moves up the plate
Why is the line drawn in pencil
Ink is mixture of different inks that will also undergo tlc
Pencil is insoluble
Why are the spots not close together
If they are too close they merge as they travel up the plate
Why is the solvent below the pencil line
So that the sample doesn’t dissolve in the solvent before it can travel up the plate
Why must you only use small spots
If it’s too big there will be too much sample so it can’t be carried by the solvent which leads to elongated smudges not clear tlc spots
Why is the plate removed before the solvent reaches the top
For a clear reference of solvent front to calculate the rf values
Why must the chamber have a lid
To have a saturated atmosphere of solvent so the plate doesn’t dry out
What is the procedure of column chromatography
A glass tube is filled with the stationary phase (alumina or silica powder to increase surface area ) or an ion exchange resin in form of small granules
A filter or plug is used to retail the solid in the tube
Solvent is added to give or all the powder
What is the stationary phase in column chromatography
Silica or alumina gel
What is the mobile phase in column chromatography
A liquid solvent (eluent)
What is the relation between retention times and solubility in column chromatography
The greater the solubility in the mobile phase the shorter its retention time and the faster it will come out of the column
How do you determine whether your solvent should be polar or non polar
A polar sample has greater solubility in a polar solvent
A non polar sample has greater solubility in a non polar solvent
What happens in gas chromatography
A column is paced with a solid or solid coated by a liquid and a gas is passed through the column under pressure at high temperature
What is the stationary phase in gas chromatography
A capillary glass or metal tube filled with a solid or a liquid adsorbed onto the solid (this is the column)
What is the mobile phase in gas chromatography
An inert carrier has such as helium, argon or nitrogen used to separate the volatile components of a mixture
How is retention then recorded in gas chromatography
At the end of the column a range of detectors identify each components for example mass spectrometry
What is gas chromatography mass spectrometry commonly used in (3)
Forensics
Environmental monitoring
Airport security system
Why is mass spectrometry used
It is sensitive enough to detect minute quantities of substances
Produced spectra which can be compared to spectra of known compounds
What is retention time based on
Difference in balance between solubility in the mobile phase and adsorption to the stationary phase
