Organic Chemistry

?
  • Created by: qaaimxz
  • Created on: 20-02-17 17:40

OA1.1 stereo-isomerism

Structural isomerism: Same molecular formula but are bonded in a different order.

Stereo-isomerism: Same molecular formula but atoms are arranged differently in space. 

Optical-isomerism: Form of stereoisomerism using non-superimposable mirror image molecules.

Chiral center: Atom bonded to 4 different groups or atoms.

Enantiomer: Non-superimposable mirror image forms of each other turning the plane of polarized light in opposite directions.

Optical Activity: Occurs in molecules with a chiral center that rotates the plane of polarized light.

Racemic Mixture: Equimolar mixture of both enantiomers that produces no overall rotation of the plane of polarized light.

Resolution: Seperation of a racemic mixture into the two enantiomers. 

1 of 39

AO1.2 Aromaticity: Kekule vs Benzene. (1)

In Kekule's structure, there are 2 bond types each having different sizes. I.e. alternating double and single bonds. X-ray studies show that all carbon-carbon lengths are the same type and the length is somewhere in between the lengths of single and double bonds. The delocalised system means all bonds are the same type and thus the same length. 

The hydration of cyclohexane is -120KJ per mole, therefore with Kekule's structure, the hydration of benzene should be -360KJ per mole. However, studies show it is actually -208KJ per mole showing benzene is more stable than expected. The delocalization of the pi orbitals would stabilize the structure and lower the energy when hydrolyzed.

3 isolated double bonds would be enough to polarize Br without a catalyst. However, benzene can only polarize Br with a catalyst present.The delocalised electron system has to less electron density to polarize the Br-Br bond.

2 of 39

AO1.2 Aromaticity: Structure of Benzene (2)

Planar molecule in a hexagonal shape

All have the same carbon to carbon bond length and type with a 120-degree angle between bonds.

Each carbon atom is bonded to 2 other carbon atoms and 2 hydrogens by a sigma bond.

The outer electron of carbon is in a 2p subshell above and below the plane which overlaps to give a delocalised electron structure. 

If benzene underwent an addition reaction, the process would disrupt the delocalised electron system and thus prefers substitution reactions. 

3 of 39

AO1.2 Aromaticity: Nitration of Benzene (3)

4 of 39

AO1.2 Aromaticity: Halogenation of Benzene (4)

5 of 39

AO1.2 Aromaticity: Alkylation of Benzene (5)

6 of 39

AO2.1: making alcohols from Halogenoalkanes (1)

Refluxing Halogenoalkane with an aqueous solution of an alkali. 

CH3CH2CH2CH2Br + NaOH --> CH3CH2CH2CH2OH + NaBr

The products are separated by fractional distillation as they have different boiling points.

This process is Nucleophilic substitution (Halogenoalkane to Alcohol)

7 of 39

AO2.1: Making alcohols by reduction (2)

Aldehyde ------------------------> Primary alcohol

Ketone------------------------> Secondary alcohol 

Reducing agents include NaBH4, but it is not strong enough for a Carboxylic acid and so LiAlH4 is used instead.

NaBH4 is much safer.

8 of 39

AO2.1: Reaction of alcohols. (3)

Alcohol + PCl5 -----------> X-Cl + POCl3 + HCl (POCl3 is a liquid and is hard to seperate)

Alcohol + SOCl2 ---------> X-Cl + SO2 + HCl  (SO2 and HCl are both gasses, easy for seperation) 

Alcohol + KBr + 50% H2SO4 ---> X-Br + KHSO4 + H2O.

(50% H2SO4 is used so HBr gas is not made)

Warm damp red phosphorus with iodine. 2P + 3I2 ---> 2PI3

Then react with alcohol. Alcohol + PI3 ---> X-I + H3PO3

9 of 39

AO2.1: ethanoyl-chloride and water (4)

Alcohol + CH3COCl ---> Ester + HCl

Gives rise to an ester

Misty fumes of HCl is given off.

Alcohol + CA ----> Ester + H2O

Reversible --> Low yield.

A little amount of concentrated H2SO4 is added and is heated under reflux and product is distilled

10 of 39

AO2.1: The acidity of Phenol's. (5)

Reactivity of phenols is different than that of alcohols.

The lone pair from oxygen overlaps with the electron system, which extends it and therefore, the Carbon-Oxygen bond in phenols is a lot stronger than in alcohols.

Phenols are stronger acids than alcohols but weaker than CA's.

CA's > Phenol > Alcohols.

11 of 39

AO2.1 Bromine and Phenol reaction. (6)

Image result for bromine + phenol (http://www.chemistryrules.me.uk/candrands/organi2t.gif)

Starts as orange and forms a colorless solution with a white PPT.

12 of 39

AO2.1: Testing for phenol's. (7)

A test for phenols can be done using Aqueous Iron (III) Chloride.

Phenols turn the solution Purple, Blue or Green.

13 of 39

OA2.2: Structure and formation (1)

Aldehyde:   Image result for aldehyde                       Ketone:Image result for Ketone       

Primary Alcohol ---------------------------> Aldehyde ---------------------------> Carboxylic acid.

Secondary Alcohol ---------------------------> Ketone.

Acidified Potassium Dichromate can be used as an oxidising agent, it turns from orange to green.

Alkaline Potassium Manganate can be used as an oxidising agent, it turns from purple to brown.

14 of 39

OA2.2: Distinguishing Carbonyl Compounds (2)

Tollens reagent is ammoniacal silver nitrate and is made up of NaOH + AgNO3 till it turns brown.

When warmed with an aldehyde a silver mirror forms on the surface.

Fehlings reagent consists of Fehlings A and Fehlings B

Fehlings A --> Aqueous solution of Cu2SO4.

Fehlings B --> Potassium silver tartrate

Warm with aldehyde and it goes from a deep blue colour to orange.

KETONES DO NOT REACT LIKE THIS.

15 of 39

OA2.2 Nucleophilic Substitution (3)

16 of 39

OA2.2: Identification of Carbonyl Compounds (4)

2,4-DNP is dissolved in acid to form Brady's reagent. 

It is mixed with the carbonyl compound to form a red/orange solid.

Heated to find the Melting point or Boiling point and is compared to known values.

17 of 39

OA2.2: Triiodomethane (Idoform) reaction (5)

CHI3 is a yellow solid.

The test looks for CH3CO groups or CH3CH(OH).

The compound reacts with I2 and NaOH.

Yellow solid forms if those two groups are present.

18 of 39

AO2.3: Acidity of CA's. (1)

Carboxylic acids > Phenol's > Water/Alcohols.

The difference in acidity is shown in the reaction with NaHCO3, Only carboxylic acids are strong enough to produce colourless bubbles of CO2.

The presence of other substituent groups may markedly alter the acidity of carboxylic acids, similar to that of phenols.

19 of 39

AO2.3: Making from Carbonyl Compounds (2)

Acidified potassium dichromate and alkaline potassium manganate are the oxidising agents. 

Acidified potassium dichromate -----------------------> Orange to Green.

Alkaline potassium manganate -----------------------> Purble to Brown.

Alcohol -----------------------> Aldehyde -----------------------> Carboxylic Acid.

20 of 39

AO2.3: Reduction of CA's (3)

Relatively stable compounds require a strong reducing agent.

NaBH4 is too weak and so LiAlH4 is used.

Image result for reduction of CH3COOH +H2O

21 of 39

AO2.3 Making aromatic CA's (4)

Image result for alkylbenzene to benzoic acids (http://img1.mnimgs.com/img/shared/discuss_editlive/4136612/2013_10_10_22_02_34/1-header16_12412444713529552.png)

All branches turn to COOH when alkylbenzene is reacted with KMnO4

22 of 39

AO2.3 Decarboxylation of CA's (5)

23 of 39

AO2.3: Esterification (6)

24 of 39

AO2.3: Ester from Acyl Chloride (7)

25 of 39

AO2.3: Acid Hydrolysis (8)

26 of 39

AO2.3: Alkaline Hydrolysis (9)

27 of 39

AO2.3: Making acid chlorides from CA's (10)

XCOOH + PCl5 -------> XCOCl3 + H3PO3

XCOOH + PCl3 ------> XCOCl3 + POCl3 HCl (Hard to seperate as HCl is a liquid)

XCOOH + SOCl2 ------> XCOCl3 + SO2 + HCl (Easy to seperate as both are gas)

28 of 39

AO2.3: Amides, Nitriles and Amines. (11)

Image result for AMIDE (http://www.ochempal.org/wp-content/images/A/amide3.png) Amide

Image result for NITRILE Nitrile 

Image result for AMINE (http://upload.wikimedia.org/wikipedia/commons/9/90/Prim._Amine_Structural_Formulae_V.1.png)  Amine

29 of 39

AO2.3: making amides and nitriles from CA's (12)

Heat CA with Urea at 120 degrees Celcius to make an amide

Dehydrate the Amide with Phosphorous pentoxide to make the corresponding nitrile.

30 of 39

AO2.3: Making Nitriles from Haloalkanes (13)

React the Halogenoalkane with KCN in a water-alcohol mixture.

Nucleophilic substitution.

31 of 39

AO2.3: Making hydroxynitriles from carbonyls (14)

React aldehyde or ketone with HCN in the presence of KCN.

Nucleophilic substitution.

32 of 39

AO2.3: General **** (15)

An amide is heated under reflux with a base, the C-N bond is broken and NH3 is made.

Nitrile is heated under reflux with Dilute Acid to make a carboxylic acid.

33 of 39

AO3.1: Making amines from Haloalkanes (1)

Halogenoalkane + Ammonia Gas ----> Amine

When heated some ammonia gas is lost and thus done in a sealed tube or excess NH3 is used.

If using excess Halogenoalkane, a secondary amine would be made.

34 of 39

AO3.1: Making Amines from Nitriles (2)

Nitriles can be reduced to Amines

Reducing agent being LiAlH4

35 of 39

AO3.1: Making aromatic amines from nitrobenzene (3

Phenylamine is made by the reduction of Nitrobenzene.

Uses tin metal and HCl heated over 100 degrees Celcius for 30 mins.

Image result for phenylamine to nitrobenzene

36 of 39

AO3.1: Ethanoylation of primary amines (4)

37 of 39

AO3.1 Making Nitrous acid (5)

38 of 39

AO3.1 Coupling reaction (6)

39 of 39

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all ALL TOPICS resources »