Organic Chemistry 2 Flashcards
Give the functional group and suffix for carboxylic acids
- COOH
- oic acid
Boiling points of carboxylic acids compared to alkanes
- Much higher
- CA contain hydrogen bonding + Van der Waals
- Alkanes only contain Van der Waals
Describe and explain the solubility trend for carboxylic acids
- Higher Mr = Lower solubility
- Low Mr acids can hydrogen bond with water
Describe how to make carboxylic acids
- Oxidise a primary alcohol to form an aldehyde
- Oxidise the aldhehyde (under reflux with acidified potassium dichromate) to from carboxylic acid
What type of acids are carboxylic acids and what do they react with?
Weak acids
React with:
- Bases
- Alkalis
- Metals
- Carbonates
(Just slower than normal acids)
What is the functional group and suffix for esters?
- COO
- anoate
Give some uses of esters
- Food flavourings
- Perfumes
- Solvents
- Plasticisers
How are esters made?
Esterification
Carboxylic acid + alcohol -> ester + water
- Reversible reaction
- Slow
- Requires warm and conc HCl or H2SO4 catalyst
How are esters collected from the products of esterification?
- Ester can be distilled off
- Boiling point is lower as it doesn’t have hydrogen bonding like water
Describe standard hydrolysis of esters
Opposite of esterification
ester + water -> carboxylic acid + alcohol
- Reversible reaction
- Slow
- Requires warm and conc HCl or H2SO4 catalyst
Describe the alternative method to hydrolyse esters
Saponification
ester + alkali -> carboxylate salt + alcohol
- Not reversible
- Faster
- Requires warm, alkali conditions
How are soaps made?
- Saponification
- By heating fats/oils with sodium or potassium hydroxide
How do soaps work?
- The hydrophilic part of the molecule attracts to the water
- The hydrophobic part of the molecule attracts to the fat
- The molecule then pulls the fat off the fabric and into the water
What is biodiesel?
A fuel that can be used in diesel engines in place of diesel made from crude oil
How are bio-diesels made?
Transesterifcation
Reacting the lipids in vegetable oils with methanol using a potassium hydroxide catalyst
Lipid + methanol -> methyl esters of fatty acids (biodiesel) + glycerol
What are arenes?
Homologous series of hydrocarbons based on benzene (C6H6)
Describe the structure of benzene
- Planar molecule
- 6 carbons form a hexagonal ring with one H atom bonded to each
- One unused electron in the P orbital of each carbon
- P orbitals overlap and electrons become delocalised
- Form an ‘electron cloud’ above and below the plane of the molecule
List the evidence to support the delocalised benzene structure
- Addition reactions
- Bond lengths
- Enthalpy of hydrogenation values
Describe how addition reactions support the delocalised structure of benzene
If benzene instead contained 3 C=C, it would readily undergo addition reactions
But it doesn’t
Describe how bond lengths support the delocalised structure of benzene
Measurements from x-ray diffraction show that carbon carbon bonds in benzene are all the same length
If the original structure was right there would be 3 long bonds (C-C) and 3 short (C=C)
Describe how enthalpy of hydrogenation values support the delocalised structure of benzene
Benzene is 152 kJ per mol stable than the original structure would be
This is because of the ‘electron cloud’ and the delocalisation stability
What are the uses of nitration?
- Production of explosives
- Producing aromatic amines which are then used to make industrial dyes
Define aliphatic amines
Amines with alkyl groups attached to the N
Define aromatic amines
Amines with the N joined directly to a benzene ring
Describe the basic nature of amines
- Bronsted-Lowry bases
- Lone pair on the N atom can readily accept a proton
List the base strength of amines
Aliphatic amines > NH3 > aromatic amines
Describe why aliphatic amines are so basic
- Alkyl groups push electrons towards the N (a positive inductive effect)
- Increases the availability of the N lone pair
- Increases ability to accept H+
Describe why aromatic amines are not so basic
- The N lone pair is partially delocalised into the benzene ring
- Reduces availability of the N lone pair
- Reduces ability to accept H+
Describe the composition of an amino acid
- Amine group
- Carboxylic acid group
- R group
What is an alpha amino acid?
An amino acid with 1 carbon between the amine group and the carboxylic acid group
Define zwitterion
An ion that has two charges at the same time
Describe the charge on an amino acid
- In the solid state, all amino acids exist as zwitterions
- H falls off carboxylic acid group and attaches to amine group
- Positive charge on N, - charge on O
Describe and explain the physical properties of amino acids
- Ionic
- Have high melting points
- Solid at room temp
- Soluble in water
List the reactions that can be undergone by the amine group of an amino acid
- Protonated by acids
- Acylation with acyl chloride/acid anhydride
- Nucleoophilic substitution with haloalkanes
List the reactions that can be undergone by the carboxylic acid group of an amino acid
- Deprotonated by bases
- Acylation
- Esterification with alcohols
Describe the preparation of aromatic amines
The reduction of aromatic nitro compounds
* Nitrobenzene + 6[H] -> Phenylamine +2H20
* To this reaction you must add Sn and HCl
- The Sn and HCl form hydrogen which reduces the nitrobenzene
- Intially a salt is formed so the NaOH is added to liberate the free amines
The reaction of NH3 and a haloalkane produces amines put is not commonly used. Why not?
This produces a mixture of primary, secondary and tertiary amines as well as quaternary salts
* If an excess of NH3 is used, then it is mostly primary amine
* If an excess of haloalkane is used, then it is mostly quaternary salt
Define addition polymer
Long chain molecules formed from lots of small molecules (monomers) join together to form a polymer, with nothing elese formed
Define condensation polymers
Long chain molecules formed from lots of small molecules (monomers) joined together to form a polymer with another small molecule formed as well
Describe how polyesters are formed
- Dicarboxylic acids + diols
- In the presence of a strong acid or specific enzyme
Describe how polyamides are formed
- Dicarboxylic acids + diamines
- In the presence of a strong acid or specific enzyme
What is the main problem with addition polymers?
- Generally unreactive and chemically inert
- So do not biodegrade
List the 3 methods of non-biodegradable polymer disposal and their problems
- Landfill - Land is limited
- Incineration - Greenhouse gases such as CO2 and toxic gases are produced
- Recycling - Seperation of pure polymers can be expensive and difficult
Why are condensation polymers better for the environment?
- Biodegradable
- Amide or ester linkages can be reacted with acids or bases in hydrolysis
Explain the difference between a polypeptide and a protein
- <50 amino acids = polypeptide
- 50+ = protein
Describe the bonding present in the secondary structure of a polypeptide
- H bonding
- N and O are very electronegative so C=O and N-H are polar
- Lone pair on O of amino aci attracted to the partially postivive H on another
What is a disulphide bond?
A covalent bond between two sulphurs
How do enzymes work as biological catalysts?
- Lock and key theory
- Active sites are stereospecific to substrates
How does enzyme inhibition work?
- Similar shape to enzyme active site
- Block the active site so no substrate can fit
Give the 4 DNA bases in their pairs
- Adenine - Thymine
- Guanine - Cytosine
Describe how nucleotides form
- Phospate attachs on the 5’ carbon in the sugar
- Bases attach to the 1’ carbon
How do you number the carbons in a deoxyribose sugar?
Number from the right of the oxygen and move clockwise
What is cisplatin and how does it work?
- cis-diamminedichloroplatinum (II)
- Cisplatin attaches to N atoms of guanine bases in a ligand replacements reaction
- This stops the DNA strands unwinding so DNA replication cannot happen
- Cancer cells can no longer divide
Describe the side-effects of treatment with cisplatin
- Hair loss
- Nausea
- Immunosuppression
Give some ways of reducing the side-effects of treatment with cisplatin
- Use lowest therapeutic dose
- Develop new drugs
- Find ways of targeting cancer cells directly
Define stationary phase
The solid used chromatography (or a liquid supported on a solid)
Define mobile phase
The liquid or gas used in chromatography
Describe paper/thin layer chromatography
- A pencil is drawn near the bottom of the paper
- A small drop of the mixture is placed on the line
- Solvent is added to just below the line
- Left to stand in a covered beaker
- Different components move up the paper at different rates depending on their relative affinities for the MP or SP
Give the Rf equation
Rf = Distance spot moved / Distance solvent moved
What if substances separated by paper chromatography are colourless?
Can be revealed using UV light or chemical staining agents such as iodine or ninhydrin
Describe column chromatography
- A column is filled with an inert solid (SP)
- Sample mixture introduced at top
- A liquid solvent (eluent) is then applied from the top (MP)
- As the solvent runs down the column the different substances in the mixture will separate out depending on their relative affinities for the MP or SP
- Retention time = time to come out of the bottom of the column
Describe gas-liquid chromatography
- Long coiled tube packed with a solid (SP)
- Sample is vapourised and injected into the instrument
- An inert gas (MP) carries the sample through the instrument under pressure and at high temp
- Retention time = time to travel through tube
- Components separated by GC re often analysed by mass spectrometer as they leave tube
What does no. of signals, position of the signals and height of signals indicate in 13C NMR?
- No. of signals - No. of c environments
- Position of signals - Chemical environment of C’s
- Heights of peaks are not relevant
What does no. of signals, position of the signals and height of signals indicate in 1H NMR?
- No. of signals - Chemical environment of H’s
- Position of signals - Chemical environment of H’s
- Height of peaks - Relative to the number of H’s causing the signal
What is the zero value in 1H NMR?
All 1H NMR is comparative to the reference compound tetramethylsilane (TMS)
Why is tetramethylsilane used as the reference compound for 1H NMR?
- Non-toxic
- Inert
- Produces a single peak
- Low boiling point (easily removed from sample afterwards)
Describe solvents used in 1H NMR
- Must not contain any hydrogens as these would also produce peaks
E.g:
* Tetrachloromethane
* Deuterated solvent (H’s replaced with an isotope of hydrogen, Deuterium)
