module 6: carboxylic acids and nitrogen compounds Flashcards
are carboxylic acids weak/strong
weak because they’re only partially ionised in solution
are carboxylic acids water soluble
less than 6C per molecule = water soluble
how can you test for a carboxylic acid
react with a carbonate(eg. Na2Co3 or NaHCO3), a carboxylic acid would produce CO2
how can an acyl chloride be formed from a carboxylic acid
carboxylic acid + SOCl2 –> acyl chloride + SO2 + HCl
outline recrystallisation
- Add minimal hot solvent to produce a saturated solution of the impure compound.
- Filter the hot solution. Remove insoluble impurities by using gravity filtration.
- Let the solution cool. As the solution cools down, the solubility of the compound decreases.
- Crystals form as the solubility of the compound decreases. As the concentration of impurities is much lower, they take longer to from crystals and hence will remain in solution.
- crystals are removed by using filtration under reduced pressure and then rinsed with cold solvent. Finally they are let dry.
how are amines classified
based on the number of R groups on the nitrogen atom
what are the properties of amines
the nitrogen atom in ammonia and amine molecules has a lone pair, allowing it to accept a proton
so they can act as bases in aqueous solutions by donating the lone electron pair to a proton and forming a dative bond
are amines or ammonia more basic
the more alkyl groups substituted onto the N atom in place of H atoms, the more electron density that is pushed on to the N atom
so more alkyl groups increases the electron density of N’s lone pair, forming a stronger base
amines are more basic
are aromatic amines or ammonia more basic
on aromatic amines the lone pair on N is partially delocalised into the benzene ring, reducing the electron density on the N atom and making it a weaker base
ammonia is more basic
how does NH3 react with haloalkanes
nucleophilic substitution
if excess haloalkane is present, then the H’s on the N can be successively replaced by the haloalkanes R group until a quaternary ammonium salt is formed
if excess amine is present, there is only one substitution
what is the mechanism of reaction for NH3 and haloalkanes
nucleophilic substitution
how are primary aromatic amines formed
- reduce nitrobenzene by reacting with tin and conc HCl
(ignore 2nd bit)
how are primary aliphatic amines formed
NH3 + haloalkanes
haloalkanes + excess, hot ethanolic ammonia
- forms mixtures and not usually primary amines
OR
reducing nitrile compounds
a two step process
1. form a nitrile from a haloalkane
2. react nitrile with a reducing agent; LiAlH4/Ni+H2
how do amino acids react
the basic amine group reacts with acids to make salts; to is protonated in neutral solutions and acids
the COOH group is deprotonated in neutral solutions and bases
what are the types of stereoisomers
geometrical (E/Z)
optical
how do chiral molecules exist
as two enantiomers (optical isomers), they are non-superimposable images of each other (like hands!!!)
how is a chiral centre marked in a drawing
with an asterisk
how do you do a 3D drawing of a tetrahedral molecule
2 solid lines - same plane as paper
1 dashed wedge - bond receding behind paper
1 solid wedge - bond coming out of paper
what are the properties of optical isomers
they are optically active and rotate plane-polarised light
one enantiomer will rotate in a clockwise direction, whilst the other routes it the same amount anticlockwise
enantiomers can sometimes be referred to as the D/L isomer
outline filtration under reduced pressure
a solid product can be separated from liquid impurities via reduced pressure filtration
- reaction mixture is poured into a Büchner funnel with a piece of filter paper in it
- the funnel is on top of a sealed sidearm flask which is connected to a vacuum line, causing it to be under reduced pressure
- reduced pressure causes suction through the funnel, making the liquid pass into the flask quickly and leaving behind dry crystals of the product
what is the general structure of an amide
what is phenol reacted with to form 2-nitrophenol/4-nitrophenol vs 2,4,6-nitrophenol
2-nitrophenol/4-nitrophenol: dilute HNO3
2,4,6-nitrophenol: conc. HNO3
what is a racemic mixture
a mixture with equal quantities of two enantiomers
how can a polyamide be formed
diamine + dicarboxylic acid
diamine + dioyl chloride
amino acids
how can a polyester be formed
diol + dicarboxylic acid
diol + dioyl chloride
hydroxycarboxylic acids
how do you name an addition polymer
poly(alkEne)
what are the features of C13 NMR spectra
- sharp signals
- signal heights aren’t proportional to the number of carbon atoms in a single molecular environment
- C atoms in different environments will give resonances with diff chemical shifts in a spectrum
- the standard reference point used is tetramethylsilane (TMS)
how is a carbon’s environment determined in C13 NMR
- the groups surrounding the carbon are looked at
- the signals will depend on what groups are attached
- the signal shows will be the higher one if there are two fun groups attached
outline how thin-layer chromatography works
separates components by aDsorbtion
1. draw pencil line near the bottom of the plate and put a spot of the mixture to be separated on the line
2. dip the bottom of the plate into a solvent
3. as the solvent spreads up the plate the different substances move with it, but different distances, so they seperate out
4. when the solvents nearly reached the top of the plate, the plate is removed and the distance that the solvent moved is marked in pencil
how can retention time be found from a gas chromatogram
the time where it peaks, these can then be looked up in a reference table to identify the substances present
how can a gas chromatogram show proportions of components in a mixture
the area under the peak will be proportional to the relative amount of substance in the original mixture
how can concentrations of substances be found from a gas chromatogram
- create a series of different concentrations of your analyte (the substance you’ve chosen to detect for your calibration)
- one at a time, inject your standard solution into a gas chromotography instrument and detect the result
- calculate the area under the graph for each standard solution
- plot this on a graph of area against concentration
- join the points to create an external calibration curve
what factors can affect retention times
- solubility: a more soluble substance will spend more time dissolved and will take longer to travel through the tube to the detector
- boiling point: high boiling point means that the substance will spend longer condensed as a lid on the tube than a gas and so will take longer to travel through the tube than if it had a lower bp
- temp of gas chromatography instrument: high temp means the substance will be evaporated for longer and move along the tube quickly; this hornets retention time for ALL substances in the tube
how do you interpret proton NMR
TMS is used for the reference peak
H nuclei with different neighbouring atoms (chemical environments) absorb at slightly different field strengths
- spin-spin coupling will split peaks into n+1 where n is the number of H on the neighbouring C atom
what solvent is used for proton NMR spectroscopy
NMR spectra are always used with molecules in solution but things like water and ethanol would form more peaks
so the H in the solvent are replaced with deuterium nuclei which don’t absorb the radio weave energy and so don’t form a peak
how can OH and NH protons be identified with proton NMR
these have v variable NMR shifts
1. run two spectra of the molecule, one of which has an some D2O added
2. if any OH or NH protons are present, they’ll swap with the deuterium and the peak will disappear
how do you calculate Rf
distance component travelled / distance solvent travelled
outline the use of two deuterated compounds in HNMR spectroscopy
CDCl3 is used as a solvent
D2O is used to identify OH or NH protons
what happens when an amino acid reacts with acid
NH3 and + ON NITROGEN
how do you find the Mr of a polyester
Mr of whole monomer x no. molecules
then subtract H2O (or whatever) multiplied by no. molecules - 1
outline the structure of an amino acid salt when reacted with excess HCl
NH2 are protonated to +NH3 and Cl- next to the N
happens to all NH2, even if on the R group
how do you test for phenol
indicator will show acidity but no CO2 formed when reacted with a carbonate
name all of the splitting patterns up to 6 neighbours
singlet
doublet
triplet
quartet
quintet
sextet
septet
