Organic 3 Flashcards
Describe the modern structure of benzene
- formula of C6H6
- six C atoms in a hexagonal ring and one H atom bonded by single sigma bonds.
- 6 p electrons delocalised in a ring structure above and below the plane of carbon atoms.
Describe kekule’s structure of benzene
- alternate single and double covalent structures between carbon atoms (starts with double)
What does it suggest if benzene is a planar molecule?
- all C-C bonds are the same length, and have a bond length and strength somewhere between the C-C and C=C bond
Explain how X‑ray diffraction shows that benzene has a delocalised structure and
not a Kekulé structure
- Shows that all C-C bonds are the same length
- in the Kekule structure, C=C bonds would have been shorter.
describe the enthalpy of hydrogenation of the kekule vs benzene vs cyclohexane structure, and how it shows that benzene is more stable than both.
- cyclohexane enthalpy = -120
so kekule will be 3x-120= -360 (expected)
But in reality, the value ended up being around -208, so less exothermic than expected.
When represented on an energy level diagram, it shows that benzene is the most thermodynamically stable.
What type of reactions does benzene usually go through?
Why?
- electrophilic substitutions
- electron density is not high enough to induce a dipole, so cannot go through addition reactions.
why is methylbenzene more reactive than benzene?
- methyl side group releases electrons into the delocalised system making it more attractive to nucleophiles.
Name the following for the reaction with benzene and halogens.
- change in functional group
- reagent
- conditions
- mechanism
- benzene to halobenzene
- halogen
- iron halide catalyst
- Electrophilic substitution
Name some observations when benzene burns.
What effects this observation?
- burns with a very sooty flame
- carbon to H ratio - the lower this is, the more sooty the flame will be.
Give the equations to form electrophiles Cl+ and Br+ from AlCl3 and FeBr3
- AlCl3 + Cl2 —> AlCl4- + Cl+
- FeBr3 + Br2 —> FeBr4- + Br+
Describe the mechanism for the halogenation of benzene
- curly arrow going from middle of electron ring to electrophile (the Br+/Cl+ etc)
- Curly arrow going from MIDDLE of bond to electron ring (which now has a + sign in the middle with only 3/4 of it actually drawn.)
- Forms a halobenzene (with halogen sticking out from an edge of a benzene ring)
Name the following for the nitration of benzene
- change in functional group
- reagent
- conditions
- mechanism
- benzene —> nitrobenzene
- Conc nitric acid in the presence of conc H2SO4 (catalyst)
- 60 Degrees
- Electrophilic substitution
Give the equation to form the electrophile NO2+ for nitration of benzene.
- HNO3 + 2H2SO4 —> NO2+ + 2HSO4- + H3O+
What is the usefulness of the nitrification of benzene?
- important to manufacture explosive material, or formation of amines which are used to manufacture dyestuffs.
Name the following for the hydrogenation of benzenes
- change in functional group
- reagent
- conditions
- type of reaction
- benzene –> cyclohexane
- Hydrogen
- nickel catalyst, 30 atm, 200 degrees.
- addition and reduction
Name the following for the Friedal Crafts Alkylation
- change in functional group
- reagent
- conditions
- mechanism
- benzene to alkyl benzene
- chloroalkane in the presence of anhydrous aluminium chloride catalyst.
- heat under reflux
- electrophilic substitution
give the equation for the electrophile CH3CH2+
AlCl3 + CH3CH2Cl —-> Ch3CH2+ + AlCl4-
Name the following for the Friedal Crafts acylation
- change in functional group
- reagent
- conditions
- mechanism
- benzene to phenyl ketone
- acyl chloride in presence of a anhydrous AlCl3 catalyst
- heat under reflux
- electrophilic substitution
Give the equation to form the electrophile CH3C=O+
AlCl3 + CH3COCl –> CH3CO+ + AlCl4-
Why are Friedel Craft reactions important/useful?
- produce a reactive functional group on the benzene ring, which is otherwise unreactive, which can then be used to produce dyestuffs etc.
- this allows the molecule to carry out subs in milder conditions.
Name 2 properties of phenols
- very weakly acidic
- will react with sodium metal and NaOH but NOT Na2CO3
Name the following for the reaction of phenol with Bromine
- change in functional group
- reagent
- conditions
- observations
- no change - will only add Brs.
- Bromine water
- room temp
- white solid forms
Compare the reaction of benzene with bromine and phenol with bromine
- phenol does not need a FeBR3 catalyst
- goes through MULTIPLE substitution reactions, whereas benzene will only undergo a single substitution reaction.
Name 3 uses of phenols
- plastics
- antiseptics
- paint resins
explain why electrophilic subs are more likely with phenols rather than benzene.
- the overlap of the -OH group and orbital.
- electrons in the p-orbital of the oxygen overlaps with the delocalised ring structure of benzene, so they become partially delocalised into the pi-system
- therefore, the electron density increases within the ring, and so is more susceptible to attack from nucleophiles.
What is the functional group of an amine?
N atom with a lone pair - can get primary, secondary, tertiary, quaternary ions and aromatic amines, which are ‘N substituted’ when it is secondary or above.
What are the two ways of making aliphatic amines?
- reacting halogenoalkane with excess ammonia
- reducing a nitrile
Name the following for the reaction of halogenoalkne with ammonia
- change in functional group
- reagent
- conditions
- mechanism
- product
- C-X to NH2
- excess ethanolic ammonia
- heat and pressure
- nucleophilic sub
- forms a primary amine and ammonium halide salt.
What is a disadvantage of making aliphatic amines using the halogenoalkane method?
Why?
- product is not pure, as it produces salts (primary, secodnary, teritary, quaternary) as well.
- because the primary amine will still have a lone pair on the N, so it can still act as a nucleophile.
Name the following for the reaction of reduction of nitriles
- change in functional group
- reagent
- conditions
- mechanism
- product
- NO2 to NH2
- Hydrogen Gas and nickel catalyst
- High temp and pressure
- Primary amine ONLY.
Give the functional group of amides
C=O-NH2 (with the Hs being subbed in for R groups)
Give 2 properties of amines
- fishy smell
- can form H bonds with water (the N and the H)
Give 2 characteristics of primary aliphatic amines
Give the reasons for these properties.
- act as Bronsted lowry bases (act as proton acceptors) because lone pair on the N can form dative bond with H+ ions.
- are stronger bases than ammonia because alkyl groups are electron releasing and push electrons towards the N, making it a stronger base.
name one property of secondary aliphatic amines
- stronger bases than primary amines, as they have more subbed in alkyl groups, so more electrons are pushed onto the N atom
Give one property of aromatic amines
- do not form basic solutions.
- this is because lone pair on the N delocalises with the delocalised ring on benzene, so the N is less able to accept protons.
what is the product of the reaction between acids and amines?
- ammonium salts
What is the product of NaOH and ammonium salts?
amine
how to make a basic buffer from amines?
weak base and salt of the weak base
eg methlyamine and methylammonium chloride
Name the following for the reaction between an acyl chloride and primary amine
- reagent
- conditions
- product
- primary amine
- room temp
- secondary amide
Name the following for the reduction of nitroarenes
- reagent
- conditions
- mechanism
- products
- Sn and HCl
- heating
- reduction
- phenylamine
Name the following for the reaction of an acyl chloride with a primary amine
- change in functional group
- reagent
- conditions
- mechanism
- acyl chloride to secondary amide
- primary amine
- room temp
- nucleophilic addition-elimination
what type of reaction is involved in making a polyamide?
- condensation polymerisation
What is the side product for polymerisation involving an acyl chloride
- HCl
What can be used to hydrolyse polyamides?
- NaOH
True or false:
Polyamides have Hydrogen bonds between the N and C on adjacent molecule
FALSE
they are between H and O of adjacent molecules
What are the func groups on an amino acid?
- NH2 and COOH
What is a zwitterion?
- an ion with a permanent dipole on either side - the H3N+, and COO-
Is the amine group acidic or basic?
basic
is the carboxyl group acidic or basic?
Acidic
Describe what will happen if an amino acid is placed into an acidic solution
- the carboxyl group will gain H+ ions, but the amine group will stay the same (H3N+)
Describe what will happen if an amino acid is placed into a basic solution
- the amine group will loose a H+ ion.
Give a method to calculate the Rf value of a amino acid.
- chromotography paper, draw pencil line from the bottom
- (general method)
- spray paper with ninhydrin and put in oven.
- calc by doing distance moved by amino acid/distance moved by solvent
Why is ninhydrin sprayed onto the chromatography paper?
- amino acids are transparent, so doing this allows red and blue spots to appear.
Describe the optical activity of amino acids, and any exceptions
- every amino acid except glycine is optically active, and will rotate plane-polarised light.
What bond is formed in proteins?
- peptide
What reagent is used to hydrolyse proteins into their constituent amino acids?
- HCl or NaOH (dilute acids or bases)
Describe how to prepare Grignard reagent
- dissolve halogenoalkane in dry ether, then react with magnesium
Grignard and methanal product
primary alcohol
Grignard with other aldehydes
secondary alcohols
Grignard with ketones
tertiary alcohols
Grignard with CO2
carboxylic acid
Give 3 ways in which the carbon chain length can be increased
- halogenoalkane reacted with KCN
- producing hydroxynitriles from carbonyls
- reacting with a grignard reagent.
state the colour change observed when alcohols are oxidised to aldehyde/ketone
orange to green
When is reflux used?
why is reflux useful?
- when heating organic reaction mixtures for a long time
- prevents volatile compounds from escaping (eg organic vapours) by condensing them back to liquids.
How to convert alkene into dihalogenoalkane under what conditions?
- Cl2, Br2, I2 etc
- room temp
How to convert ketone/aldehyde to hydroxynitrile?
- HCN in the presence of KCN.
How to convert aldehyde to carboxylic acid?
- acidified K2Cr2O7
- heat under reflux
How to convert acyl chlorides to esters?
- react with alcohol at room temp
How to convert acyl chlorides to primary amide?
react with NH3 at room temp
How to convert acyl chlorides to carboxylic acids?
- hydrolysis reaction with water
How to convert acyl chlorides to secondary amide?
- react with primary amide.
How to convert nitrile to amine?
- reduction with LiAlH4
How to convert alkene to diol?
- steam and phosphoric acid catalyst
- at 60 atm and 300 degrees Celsius
How to convert alcohol to halogenoalkane?
- PCl5/NaBr and H2SO4/red phosphorus and I2
- heat under reflux
How to convert halogenoalkane to alcohol?
- ## react with NaOH and H20,warm
How to convert nitrile to carboxylic acid?
- acid hydrolysis
- heat with HCl
How to convert halogenoalkane to amine?
- NH3,
heat
How to convert Halogenoalkane to carboxylic acid in 2 step synthesis
- Mg in dry ether,(grignard reagent) and then react product with CO2 in diltue acid
Explain why the filter paper and funnel are warmed in an oven before gravity filtration
(2)
- to make sure solution doesn’t cool down significantly
- this could decrease premature crystals forming during filtration
Explain why 1. cooling and recrystalising and 2. filtering the crystals under reduced pressure purifies the product.
- the product is less soluble in colder solvent
- reduced pressure allows more soluble impurities to be filtered out.
What are 2 words that describe the Grignard reagent?
- nucleophile
- reducing agent
