Edexcel Chemistry - Topic 17: Organic II

?
  • Created by: Ryan C-S
  • Created on: 09-04-18 19:25

Chirality

  • Optical Isomerism (Chirality) occurs in carbon compounds containing 4 different groups attached to a carbon e.g. Amino Acids.
  • Chiral molecules are mirror images of one another and are not superimposable with one another.
  • Two molecules that are optical isomers of each other are enantiomers.
  • Chiral molecules have similar physical and chemical properties but rotate plane polarised light in different directions
  • The Dextrorotatory enantiomer will rotate light clockwise (+)
  • The Laevorotatory enantiomer will rotate light anticlockwise (-)
  • Some enantiomers give a different flavour (e.g. spearmint and caraway) and some drugs have one safe enantiomer (e.g. Thalidomide)
    Image result for chirality
1 of 30

Racemic Mixtures

  • A racemic mixture contains a 50:50 mixture of two enantiomers
  • It will not rotate plane-polarised light
  • Racemic mixtures form when a trigonal planar reactant or intermediate is attacked from both sides during a reaction mechanism (e.g. HCN reacting with aldehydes and asymmetrical ketones)
  • There is an equal chance of forming each enantiomer so a racemic mixture forms

Image result for formation of racemic mixture

2 of 30

Aldehydes: Properties

  • General formula: RCHO
  • Suffix = -al (e.g. Ethanal)
  • Contains a carbonyl group (C=O bond)
  • Can form permanent dipole interactions and are soluble in water
  • Aldehydes are used in preservatives, flavourings and perfumes

Image result for aldehyde

3 of 30

Ketones: Properties

  • General Formula: R1COR2
  • Suffix = -one (e.g. Propanone)
  • Contains a carbonyl group (C=O bond)
  • Can form permanent dipole interactions and are soluble in water
  • Ketones are used in nail polish removers, embalming fluids, perfumes and pesticides

Image result for ketones

4 of 30

Oxidation of Aldehydes

  • Reaction: Aldehyde --> Carboxylic Acid
  • Reagent: Potassium Dichromate(VI) and dilute sulphuric acid
  • Conditions: Heat under reflux
  • Observations: Colour change - Orange > Green
  • Aldhydes can also be oxidised to Carboxylic Acids by addition of either Tollens Reagent or Fehling's Solution
  • Tollens Reagent - Formed by mixing aqueous ammonia with silver nitrate to form [Ag(NH3)2]+
    Conditions: Heat gently
    Reaction: Aldehydes are oxidised into a carboxylic acid and the silver(I) ions reduced to silver atoms
    Observations: A silver mirror forms
  • Fehling's Solution - A solution of Cu2+ ions
    Conditions: Heat gently
    Reaction: Aldehydes are oxidised into a carboxylic acid and the Cu2+ ions reduced to Cu2O
    Observations: Colour Change - Blue Solution > Red Precipitate
5 of 30

Oxidation of Ketones

  • Ketones DO NOT oxidise on reaction with Potassium Dichromate(VI) and dilute sulphuric acid and the orange colour will remain
  • Addition of Fehlings solution causes the blue colour of the copper(II) ions to remain
  • Addition of Tollen's Reagent does not cause the silver ions to be reduced to silver atoms
  • Ketones are unable to be oxidised because unlike an aldehyde where there is a free hydrogen which can be oxidised further, a ketone has two carbon chains next to the carbonyl group
6 of 30

Reduction of Carbonyls

  • Reaction: Aldehyde/Ketone --> Alcohol
  • Reagents: Lithium tetrahydridoaluminate (LiAlH4)
  • Conditions: Room temperature and pressure

LiAlH4 acts as a reducing agent. Other reducing agents (e.g. Sodium tetrahydridoborate - NaBH4) can be used

Aldehydes are reduced to a Primary Alcohol
Ketones are reduced to a Secondary Alcohol

Image result for reduction of carbonyls

7 of 30

Formation of Hydroxynitriles

  • Reaction: Aldehyde/Ketone --> Hydroxynitrile
  • Reagents: HCN in the presence of KCN
  • Conditions: Room temperature and pressure
  • Mechanism: Nucleophilic Addition

When naming a nitrile, the CN becomes part of the main chain

CH3COCH3 + HCN --> CH3C(OH)(CN)CH3
propanone + hydrogen cyanide --> 2-hydroxy-2-methylpropanenitrile

Image result for carbonyl to hydroxynitrile

8 of 30

Reaction of Carbonyls with 2,4-DNP

  • 2,4-dinitrophenylhydrazine (2,4-DNP) reacts with both Aldehydes and Ketones.
  • The product is an orange precipitate so the reaction can be used as a test for a carbonyl group in a compound
  • Fehling's Solution or Tollen's Reagent have to be used to distinguish between whether a compound is an Aldehyde and a Ketone

Image result for reaction of a carbonyl with 24dnp

9 of 30

Reaction of Carbonyls with Iodine

  • Reaction: Carbonyl --> Triiodomethane
  • Reagents: Iodine and NaOH
  • Conditions: Warm very gently
  • Observations: Yellow crystaline precipitate with an antiseptic smell

The reaction only works if there is a methyl group next to the C=O bond. Ethanal is the only aldehyde that reacts. More commonly are methyl ketones e.g. Propanone.
The reaction is called the Iodoform Test

CH3COCH3 + 3 I2 + 4 NaOH --> CHI3 + CH3COONa + 3NaI + 3H2O

10 of 30

Carboxylic Acids: Properties

  • General Formula: RCOOH
  • Suffix = -oic acid
  • Carboxylic Acids can form hydrogen bonds so are soluble in water
  • Carboxylic Acids are weak acids in water and only slightly dissociate, but are strong enough to displace carbon dioxide from carbonates
  • Carboxylic Acids delocalise (the pi charge cloud spreads out) to form stable ions/salts
  • Carboxylic Acids are found in vinegar and cream of tartar

Image result for carboxylic acid

11 of 30

Strength of Carboxylic Acids

  • Longer carbon chains pushes electron density onto the COO- ion making it more negative and less stable - therefore the acid is weaker
  • Propanoic acid is less acidic than ethanoic acid
  • Highly electronegative chlorine atoms withdraw electron density from the COO- ion making it less negative and more stable - therefore the acid is stronger

Image result for strength of carboxylic acids

12 of 30

Preparation of Carboxylic Acids

  • Reaction: Primary Alcohol/Aldehyde --> Carboxylic Acid
  • Reagent: Potassium Dichromate(VI) and dilute sulphuric acid
  • Conditions: Use of excess dichromate and heat under reflux
  • Observation: Colour Change - Orange > Green

Image result for alcohol to carboxylic acid

13 of 30

Reduction of Carboxylic Acids

  • Reaction: Carboxylic Acid --> Primary Alcohol
  • Reagents: Lithium tetrahydridoaluminate (LiAlH4) in dry ether
  • Conditions: Room temperature and pressure

LiAlH4 acts as a reducing agent

Image result for reduction of carboxylic acid

14 of 30

Hydrolysis of Nitriles

  • Reaction: Nitrile --> Carboxylic Acid
  • Reagents: Dilute hydrochloric/sulphuric acid
  • Conditions: Heat under reflux

Image result for acid hydrolysis of a nitrile

15 of 30

Salt Formations of Carboxylic Acids

ACID + METAL (Na) --> SALT + HYDROGEN
2CH3COOH + 2Na --> 2CH3COO-Na+ + H2

ACID + ALKALI (NaOH) --> SALT + WATER
CH3COOH + NaOH --> CH2COO-Na+ + H2O

ACID + CARBONATE (Na2CO3) --> SALT + WATER + CARBON DIOXIDE
2CH3COOH + Na2CO3 --> 2CH3COO-Na+ + H2O + CO2

*Effevescence from the production of CO2 when a carboxylic acid reacts with Sodium Carbonate can be used as the test for a Carboxylic Acid

16 of 30

Reaction with Phosphorus(V) Chloride

  • Reaction: Carboxylic Acid --> Acyl Chloride
  • Reagents: Phosphorus(V) Chloride - (PCl5)
  • Conditions: Room temperature and pressure
  • Observations: Steamy fumes of HCl will form

CH3COOH + PCl5 --> CH3COCl + POCl3 + HCl

Image result for carboxylic acid to acyl chloride reaction

17 of 30

Oxidation of Methanoic Acid

  • Carboxylic acids cannot be oxidised with the exception of methanoic acid as it has a structure similar to an aldehyde
  • Methanoic acid is oxidised into carbonic acid (H2CO3)

HCOOH + [O] --> HOCOOH

Image result for methanoic acid Image result for carbonic acid

18 of 30

Acyl Chlorides: Properties

  • General Formula: RCOCl
  • Suffix = -yl Chloride
  • Acyl Chlorides are a carboxylic acid derivative that are more reactive
  • The chlorine is more easily lost because of less effective delocalisation making Acyl Chlorides more reactive
  • Acyl Chlorides are used for creating other organic chemicals due to their reactivity

Image result for acyl chloride use

19 of 30

Reaction of Acyl Chlorides with Water

  • Reaction: Acyl Chloride --> Carboxylic Acid
  • Reagent: Water
  • Conditions: Room temperature and pressure
  • Observations: Mitsy fumes of HCl

Image result for reaction of acyl chloride with water

20 of 30

Reaction of Acyl Chlorides with Ammonia

  • Reaction: Acyl Chloride --> Primary Amide
  • Reagent: Ammonia
  • Conditions: Room temperature and pressure
  • Observations: White smoke of NH4Cl produced

Image result for reaction of acyl chloride with ammonia

21 of 30

Reaction of Acyl Chlorides with Primary Amides

  • Reaction: Acyl Chloride --> Secondary Amide
  • Reagents: Primary Amine
  • Conditions: Room temperature and pressure

RCOCl + 2 CH3NH2 --> RCONHCH3 + CH3NH3+Cl-

Image result for reaction of acyl chloride with primary amine

22 of 30

Esters: Properties

  • General Formula: R1COOR2
  • Suffix = -yl -oate
  • Esters form on the reaction of an alcohol with either a carboxylic acid or an acyl chloride
  • The -yl part of the name comes from the alcohol reacting e.g. Methanol = Methyl-
  • The -oate part of the name comes from the carboxylic acid or acyl chloride reacting e.g. Ethanoic Acid = Ethanoate
  • Esters don't form hydrogen bonds and are almost insoluble in water
  • Esters are used in perfumes as they are sweet smelling, volatile and don't react with water

Image result for ester

23 of 30

Esterification

  • Reaction: Carboxylic Acid + Alcohol ⇌ Ester + Water
  • Catalyst: Sulphuric acid
  • Conditions: Heat under reflux

The formation of an ester with a carboxylic acid is a reversible reaction, slow and a low yield is produced

  • Reaction: Acyl Chloride + Alcohol --> Ester + HCl
  • Conditions: Room temperature and pressure
  • Observations: Steamy fumes of HCl are evolved

The formation of an ester from an acyl chloride is a better reaction because:

  • It is quicker
  • It is not a reversible reaction
  • It produces higher yields and is more efficient
24 of 30

Hydrolysis of Esters

  • Reaction: Ester + Water ⇌ Alcohol + Carboxylic Acid
  • Reagents: Dilute hydrochloric acid and excess water
  • Conditions: Heat under reflux

This reaction is reversible and doesn't give a good yield of either product

  • Reaction: Ester --> Carboxylic Acid Salt + Alcohol
  • Reagents: Sodium Hydroxide
  • Conditions: Heat under reflux

The anion is resistant to attacks by weak nucleophiles e.g. alcohols so the reaction is not reversible

Image result for hydrolysis of esters

25 of 30

Triglycerides

  • Triglycerides are naturally occuring esters consisting of three carboxylic acids bonded to propane-1,2,3-triol (glycerol) important for energy stores in biological systems
  • Ester bonds are links between the carboxylic acids and glycerol that form in a condensation reaction 
  • Condensation reactions are reactions that join two molecules by releasing a water molecule
  • The carboxylic acid chain can be either saturated (only C-C bonds) or unsaturated (contains C=C double bonds)
  • Saturated fats are solids at room temperature as the chains can pack together easily so the Van der Waals forces act stronger increasing melting point

Image result for triglycerides

26 of 30

Polyesters

  • Polyesters are a condensation polymer
  • Condensation polymers add two monomers together by releasing a water molecule
  • Polyesters can be formed by the following reactions:
    Dicarboxylic Acid + Diol --> Poly(ester) + Water
    Diacyl Chloride + Diol --> Poly(ester) + HCl
  • Using carboxylic acids to make a polyester would mean an acid catalyst is required and an equilibrium will be established
  • Using acyl chlorides to make a polyester results in a more reactive reaction that goes to completion without the need for a catalyst but does result in the production of toxic HCl fumes

Image result for polyesters

27 of 30

Terylene

  • Monomers: Benzene-1,4-dicarboxylic acid and Ethane-1,2-diol
  • Terylene is used in clothing because it is strong, flexible, hard waring and washable
  • Terylene can be treated by stretching and heating to make it stronger for use in drinks bottles and food containers

Image result for terylene

28 of 30

Poly(lactic acid)

  • Monomer: 2-hydroxypropanoic acid
  • Poly(lactic acid) - PLA - is a biodegradable polymer used in plastics, plannt pots, disposable nappies and absorbable surgical sutures (stiches)
  • The reaction joins muliple monomers of lactic acid together in a condensation polymer

Image result for polylactic acid

29 of 30

Chemical Reactivity of Poly(esters)

  • Polyesters are biodegradable (can be broken down by hydrolysis)
  • Polyesters can be hydrolysed by acids and alkalis

With HCl

  • A polyester splits up into the original dicarboxylic acid and diol

With NaOH

  • A polyester splits up into the a diol and a dicarboxylic acid salt

Image result for hydrolysis of polyesters

30 of 30

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all Functional Groups resources »