Unit 3: Section 9 - Further Synthesis and Analysis MDY * Flashcards
organic synthesis * NMR spectroscopy * 1H NMR * chromatography more on chromatography
how to make a secondary/tertiary amine and their salts from a halogenoalkane?
ammonia
heat
not primary halogenoalkane
how to make a primary amine from a halogenoalkane?
ammonia
heat
primary halogenoalkane
how to make an alkene from a halogenoalkane?
KOH
ethanol
reflux
how to make a nitrile from a halogenoalkane?
aqueous KCN
ethanol
reflux
how to make an alcohol from a halogenoalkane?
warm aqueous NaOH
reflux
how to make a halogenoalkane form an alkene?
20*C
how to make dibromo alkane from an alkene?
Br2
20*C
this is the test for unsaturation
how to make an alcohol from an alkene?
H3PO4 catalyst
stream
300*C
60 atm
how to make an alkene from an alcohol?
concentrated H2SO4
reflux
how to make a primary amine from a nitrile?
LiAlH4
dilute H2SO4
how to make a carboxylic acid from an alchol?
K2Cr2O7
H2SO4
reflux
primary alcohols
how to make an aldehyde/ ketone from an alcohol?
K2Cr2O7
H2SO4
distillation
not tertiary alcohols
how to make an alcohol from an aldehyde/ketone?
NaBH4
in water
methanol
how to make a hydroxy nitrile from an aldehyde/ ketone?
aqueous KCN
H2SO4
20*C
how to make a carboxylic acid from an aldehyde/ketone?
K2Cr207
H2SO4
reflux
how to make an ester from a carboxylic acid?
alcohol
concentration H2SO4 catalyst
heat
how to make a carboxylic acid from an ester?
dilute H2SO4 catalyst H2O reflux OR dilute aqueous NaOH reflux
how to make a carboxylic acid from an acyl chloride / acid anhydride?
H2O
20*C
how to make an ester from an acyl chloride / acid anhydride?
alcohol
20*C
how to make a primary amide from an acyl chloride / acid anhydride?
NH3
20*C
how to make an N-substituted amide from an acyl chloride / acid anhydride?
amine
20*C
what 2 addition reactions can benzene do?
acylation
nitration
what happens in the acylation of benzene?
benzene + RCOCl –> phenyl ketone
AlCl3 catalyst
reflux
non-aqueous environment
what happens in the nitration of benzene?
concentrated HNO3 + benzene –> nitrobenzene
concentrated H2SO4
below 55*C
how to make an Aromatic amine from a nitrobenzene?
in reduction Sn concentrated HCl reflux then add aqueous NaOH
how to make an N-phenylethanamide from an aromatic amine?
CH3COCl
how are chemists designing safe and efficient synthesis routes?
avoiding using solvents to reduce hazards and waste
solvents are often flammable and toxic so pose safety risks
if solvents have to be disposed of after the reaction they are wasteful
what does NMR spectroscopy stand for?
nuclear magnetic resonance spectroscopy
what are the 2 types of NMR spectroscopy?
13C NMR - how carbon toms are arranged
1H/ proton NMR - how hydrogen atoms are arranged
how does NMR spectroscopy work?
an atomic nucleus with an odd number of nucleons has a nuclear spin, giving it a weak magnetic field.
NMR spec looks at how this magnetic field reacts when put in a much larger external magnetic field
how does NMR work on hydrogen and carbon?
hydrogen nuclei are single protons, so they have spin
carbon usually has 6 protons and 6 neutrons so does no have spin, but 13C carbons have 7 neutrons so they have spin
what happens to the magnetic fields in nuclei in NMR spectroscopy?
normally nuclei spin in random directions so the magnetic fields cancel out
but when a strong magnetic field is applied they all align with the field or opposed to it
aligned nuclei have a lower energy level
what do radio waves do to aligned nuclei?
radio waves of the right frequency can give nuclei enough energy to flip to a higher energy level.
opposed nuclei can emit radio waves to flip down to a lower energy level
what does the flipping of nuclei in NMR do?
there are more aligned nuclei to start with so there will be an overall absorption of energy when they are flipped, NMR spectroscopy measures this absorption
why do nuclei in different environments absorb different amounts of energy?
a nucleus is shielded from the effects of external magnetic fields by its surrounding electrons
atoms or groups of atoms around the nucleus affect shielding
so nuclei feel different magnetic fields based on environment, absorb different amounts of energy at different frequencies
what is an atom’s environment?
the different bonds and atoms a nucleus is surrounded by
for 2 atoms to be in the same environment, they must be joined to the exact same things
what is chemical shift?
the difference between the frequencies of energy absorbed by a nucleus relative to a standard substance
it is the horizontal scale on an NMR spectrum
what standard substance is used in NMR?
tetramethylsilane
TMS
Si(CH3)4
why is TMS used as a standard substance?
it has 12 hydrogens with the same environment so it produces a single absorption peak far away from other absorption peaks
non-toxic
inert
low boiling point (easy to remove)
how is chemical shift measured?
in parts per million (ppm) relative to TMS
TMS is given a chemical shift value of 0
what does the number of peaks on an NMR spectrum tell you?
how many different environments are present in a particular molecule
what does the size of a peak on a 1H NMR spectrum tell you?
the relative area under each peak is the relative number of protons with that environment
its size may be represented as a number above the peak
what do splitting patterns mean?
each spike will be split into smaller peaks
the number of peaks = the number of hydrogens on the neighbouring carbon + 1
if a neighbouring carbon’s hydrogens have the same environment only count the hydrogens on 1 of the carbons
what are the different splitting paterns?
singlet = 1 peak = 0 H doublet = 2 peaks = 1 H triplet = 3 peaks = 2 H quartet = 4 peaks = 3 H multiplet = >4 peaks = >3 H
what solvents are used to dissolve samples for 1H NMR spectroscopy?
deuterated solvents
CCl4 - no H atoms
why are deuterated solvents used in NMR?
hydrogen atoms are replaced with deuterium (hydrogen with 2 nucleons s it doesn’t have spin)
what does it mean if a peak lies more to the left in NMR?
the closer a carbon/hydrogen lies to the more electronegative group the further to the left it lies on the spectrograph
what does 1H NMR tell us?
how many 1H atoms are present
Information about chemical environment of 1H atoms
what the H atoms are next to
Where does 1H NMR take place (conditions)?
1H NMR spectra are always recorded in solution
if the solvent contains any 1H atoms, then these will appear in the spectrum
solvents are used that don’t contain 1H atoms
what are equivalent atoms?
atoms in the same chemical environment
what are non-equivalent atoms?
atoms in different chemical environments
what is spin coupling?
a hydrogen on an adjacent carbon influences the magnetic field of those around it
the effect of spin-spin coupling is to split a single peak into a cluster
what does high resolution NMR do?
tells us about protons on adjacent carbons to the nuclei we are looking at
when doesn’t coupling occur (peaks not split)?
it doesn’t happen to H’s that are equivalent
H’s on Oxygens or nitrogen
what does the hydrogen in an alcohol look like?
no coupling with the H on oxygen
H on O has no impact on other groups
singlet
what is chromatography used for?
to separate stuff in a mixture - once it’s separated, you can identify the components
what is the mobile phase?
where the molecules can move. this is always a liquid or a gas
what is the stationary phase?
where the molecules can’t move. this must be a solid, or a liquid on a solid support
what happens in chromatography?
mobile phase moves through or over the stationary phase
and components separate out
what determines the distance moved by each substance in chromatography?
the distance each substance moves up the plate depends on its solubility in the mobile phase and its retention by the stationary phase
components more soluble in the mobile phase - travel further up plate
what is the stationary phase in thin layer chromatography?
a thin layer of silica or alumina fixed to a glass or metal plate
how to see the chromatogram of colourless chemicals?
fluorescent dye that glows in UV light, added to mobile phase
dark patches show where chemicals are
expose chromatogram to iodine vapour - its a locating agent, it sticks to the chemicals and shows up as brown/purple spots
what is the formula for Rf?
distance travelled by spot / distance travelled by solvent
how will Rf change?
if you change the composition of the TLC plate, the solvent or temperature
its hard to keep conditions identical, so put all comparative compounds on the same plate
what is column chromatography used for?
for purifying an organic product
what is the stationary phase in column chromatography?
packing a glass column with a slurry of an absorbent material such as aluminium oxide powder coated with water - the stationary phase
it has a large surface area
what happens in column chromatography?
mixture added to top of column and allowed to drain down into slurry
solvent then run slowly and continually through the column
as mixture is washed through, its components separate out according to how soluble they are in mobile phase and how strongly they are adsorbed onto stationary phase
when is gas chromatography used?
when you have a mixture of volatile liquids
what is the stationary phase in gas chromatography?
a solid or a solid coated by a viscous liquid like oil, packed into a long tube. the tube is coiled to save space and built into an oven.
what is the mobile phase in gas chromatography?
an unreactive carrier gas such as nitrogen
how are compounds identified identified in gas chromatography?
each component takes a different amount of time from being injected into the tube to being recorded as a peak at the other end - retention time
what does the area under each peak tell you in gas chromatography?
the relative amount of each component that’s present in the mixture
what is gas chromatography used for
to find level of alcohol in blood or urine
to find proportions of various esters in oils used in paints
forensics
environmental analysis
airport security
space probes
what is gas chromatography-mass spectrometry?
the sample is separated using gas chromatography, but instead of going to a detector, the separated components are fed into a mass spectrometer
it produces a mass spectrum for each component, which can be used to identify each one and show what the original sample consisted of
what is the advantage of GC-MS?
the components separated out by chromatography can be positively identified, which can be impossible from a chromatogram alone
reference retention time not needed
how can GC-MS be fully automated?
computers can be used to match up the mass spectrum for each component mixture against a database
what are the limitations of chromatography?
similar compounds have too similar Rf values
unknown compounds have no Rf value for comparison
it is hard to find a solvent that will have the correct amount of solubility
