Organic (2) Flashcards
Functional group of nitriles
CN
Give the functional groups of 2 derivates of Carboxylic acids
- esters: COO
- Acyl Chlorides - COOCl
Functional group of amides
- NH2
define structural isomer
- same molecular formula, diff structural formula.
position isomer
same molecular formula, but diff position of functional groups
Functional group isomers, give an example.
same molecular formula, but arrange to give diff functional groups. eg alcohol to ether.
where is the COO in aldehydes?
end
where is the COO in ketones?
middle.
stereoisomerism
- same structural formula, diff arrangement of atoms in space.
Optical isomerism components (what is needed for it to happen?)
- 4 diff groups need to be attached to a carbon (an asymmetric carbon)
- four groups arranged tetrahedrally around the C.
enantiomers
- 2 compounds that are optical isomers of each other.
- are nonsuperimposable.
give some properties of optical isomers
- can rotate plane polarised light
- similar chemical and physical properties.
define a racemic mixture
- a mixture containing 50/50 of enantiomers.
Give 1 property of a racemic mixture
- will not rotate plane polarised light.
- because one will rotate clockwise, and one anticlockwise, so will cancel out.
why is trying to separate a racemic mixture extremely difficult?
- very expensive
- same chemical and physical properties.
how do you form a racemate? (mechanism wise)
- forms when a trigonal planar reactant or intermediate is approached by 2 species attacking from either side.
Which type of mechanism can actually form a racemate?
- Sn1 only (happens in 2 steps)
Describe the Sn1 mechanism to form a racemate.
- any species attached to Carbon breaks off, forming a carbocation intermediate.
- this is planar
- 2 species can now either attack from the top or bottom, resulting in diff enantiomers forming.
- can tell when it is a racemate, as will no longer rotate plane-polarised light.
Describe the Sn2 mechanism
- species attacks the carbon (slightly positive) and then jumps off to another delta negative species, breaking it off
- forms a transition stage.
- cannot form racemic mixture, only forms one enantiomer. (so will still rotate plane polarised light)
what two types of reactions can form a racemate?
- nucleophilic addition, and electrophilic addition.
describe and explain the trend in solubility of carbonyls in water
- smaller the carbonyl, the more soluble in water it is.
- because it can form H bonds with water.
- pure carbonyls cannot form hydrogen bonds, but can bond by forming permanent dipole-dipoles.
describe the reaction, reagent and conditions and observations of the oxidation of aldehydes
Reaction: aldehyde—> carboxylic acid
Reagent: acidified K2Cr2O7 (with H2SO4)
conditions: heat under reflux.
observations: orange to green, as the Cr2O72- ion is reduced to the Cr3+ ion.
Give the conditions and test for aldehydes
- tollens reagent, heat gently (eg with water bath)
- will form a silver mirror.
Give another test and conditions for aldehydes
- Fehling’s solution, heat gently (eg with water bath)
- blue to brick red.
describe the reaction, reagent and conditions and observations of the reduction of carbonyls.
reaction: carbonyl —> alcohol (primary for aldehydes, secondary for ketones)
reagent: NaBH4 (sodium tetrahydroborate) in dry ether.
conditions: room temp and pressure
describe the reaction, reagent and conditions, observations and mechanism of HCN to a carbonyl.
reaction: carbonyl —> hydroxynitrile
Reagent: HCN in the presence of KCN
Conditions: room temp and pressure
Mechanism: nucleophilic addition.
describe the reaction, reagent and conditions, observations and mechanism of the reaction between iodine and a carbonyls.
reaction: forms a salt and CHI3
reagent: iodine and NaOH
conditions: warm very gently
Observations: yellow ppt and antiseptic smell.
Describe the test of 2,4DNP with carbonyls.
How can you further identify it?
- reagent: 2,4 DNP
- result: orange ppt in presence of carbonyl group.
- can use the melting point of the crystal formed to help identify which carbonyl was used, compare values to known values in a database.
why are carboxylic acids soluble in water?
- can form H bonds with water.
How are Carboxylic acid salts stabalised?
- by delocalisation, makes dissociation more likely.
Name 4 methods to prepare carboxylic acids.
- full oxidation of primary alcohols
- oxidation of aldehydes
- Hydrolysis of nitriles
- waterand acyl chloride
describe the reaction, reagent and conditions, observations and mechanism of full oxidation of primary alcohols
- forms carboxylic acid
- reagent: acidifed (with H2SO4) Pottasium Dichromate.
- conditions: heat under reflux, excess of dichromate, distill off product once reaction is finished.
describe the reaction, reagent and conditions, observations and mechanism of reduction of carboxylic acids
- forms alcohol
- reagent: LiAlH4 in dry ether (reducing agent)
- conditions: RTP
Name a functional group test for carboxylic acids
- react acid with solid sodium carbonate or aq sodium hyrdogen carbonate.
- effervescence produced, CO2 produced.
Which is the only acid that can’t be oxidised by an oxidising agent? why? what does it form instead?
- methanoic acid
- effectively has an aldehyde group
- forms carbonic acid, which decomposes to give CO2
describe the reaction, reagent and conditions, observations and mechanism of the reaction between carboxylic acids and PCl5
- forms acyl chloride
- reagent: PCl5
- conditions: room temp
-observations: white steamy fumes HCl.
How do you name esters?
-yl bit comes from alcohol
-anoate bit comes from carboxylic acid.
How to you form esters?
- alcohol and carboxylic acid react together
- need acid catalyst, as it is a reversible reaction.
Name 3 uses for esters
- food flavourings, perfumes, solvents for organic polar substances.
Why do esters not form H bonds?
- no hydrogen in an ester is bonded to a highly electronegative atom.
Name 2 ways in which esters can be hydrolysed.
give some details.
- with NaOH - complete
- with dilute HCl- reversible
both are heated under reflux.
What properties do esters need to have in order to be used in perfumes.
- non toxic
- soluble in solvent like ethanol
- volatile
- not react with water.
give some properties of acyl chlorides
give reasons.
- highly reactive (more reactive than carboxylic acids) due to its double dipole (C=O and C-Cl)
- Cl group classed as a good leaving
describe the reaction, reagent and conditions, observations and mechanism of acyl chlorides with water
- reagent: water
- forms carboxylic acid.
- conditions: room temp.
- white steamy fumes of HCl given off.
describe the reaction, reagent and conditions, observations and mechanism of acyl chlorides with ammonia.
reagent: ammonia
- forms primary amide
- conditions: room temp.
- white SMOKE of NH4Cl given off.
describe the reaction, reagent and conditions, observations and mechanism of a acyl chloride with a primary amine
- reagent: primary amine
- forms secondary amide
- conditions: room temp
describe the reaction, reagent and conditions, observations and mechanism of acyl chlorides with alcohol.
what are the advantages of this reaction?
- reagent: alcohol
- forms an ester
- conditions: room temp.
- observations: white steamy fumes of HCl given off.
advantages:
- not reversible, so has a higher yield
- much quicker
- no high temp needed, so saves on energy costs.
what is the product formed when esters are hydrolysed with dilute acid.
What are the conditions needed for this reaction?
Any other info?
- forms alcohol and carboxylic acid
- heat under reflux
- is reversible
what is the product formed when esters are hydrolysed with NaOH?
What are the conditions needed for this reaction?
Any other info?
- forms salt and alcohol
- heat under reflux.
- is non reversible.
describe the reaction, reagent and conditions, observations of acyl chlorides with water
- forms a carboxylic acid
- reagent: water
- conditions: room temp.
- observation: white steamy fumes of HCl given off
what will a polyester hydrolyse to give (with HCl)
- diol and dicarboxylic acid
what will a polyester hydrolyse to give (with NaOH)
- diol and diacyl chloride salt.
