Edexcel A Level Chemistry: 17: Organic Chemistry II

Stereoisomerism

Compounds with the same molecular formula but with different structural formula

They differ because they have different functional groups

Differ because they have different patterns of branching in their carbon chains

Differ because the same functional group is attached to different carbon atoms in the chain

Have the same structural formula but differ because their atoms or groups are arranged differently in three dimensions

Differ because their atoms or groups are attached at different positions on opposite sides of a C-C double bond

Two or more molecules that appear identical but cannot be superimposed onto one another.

Carbons with four different atoms or groups attached

Light in which oscillations exist in planes at right angles to the direction of travel.

Materials such as Polaroid, which absorb all of the oscillations expect those in a single plane

The use of a polarimeter to measure the amount of optical activity, if any, of a substance.

One of only one colour or frequency

A polarising filter that converts unpolarised light into plane polarised light

The plane of polarisation will be rotated so it is no longer vertical - Clockwise = dextrorotatory, Anticockwise = laevorotatory

The analyser

It is rotated to a position here the maximum light intensity can be seen. The angle of rotation is measured and quoted.

Yes - apart from the direction in which they rotate plane polarised light.

Yes - apart from the way they react with enantiomers of other substances

One containing equal amounts of two enantiomers.

S = substitution N= nucleophillic 2=bimolecular and second order

S = Substitution N = Nicleophillic 1 = unimolecular and first order

Because of the inversion that occurs in the SN2 mechanism, the optical activity of the product is different to that of the reactant. If the reactant is dextrorotatory, the product will be laevorotatory and vice versa.

If the reaction is via SN1, there will be no optical activity in the product.

C=O

Aldehydes and Ketones

A hydrogen joined to a carbonyl group

If there are only hydrocarbon groups joined to the carbonyl

They form polar bonds, because oxygen is much more electronegative than carbon

The have distinctive smells - short carbon chains = unpleasant, long carbon chains = pleasant

Alkanes < Aldehydes < Ketones < Alcohols

They have intermediate intermolecular forces, only dipole dipole, so hydrogen bonds are not able to form because all the hydrogen atoms are attached to carbon atoms only.

Smaller aldehydes and ketones are soluble because they can form hydrogen bonds with water. Solubility decreases with chain length

Alcohols

Lithium Aluminium Hydride

With both the carbonyl and reducing agent in dry ether

Acidified potassium dichromate, Fehling’s, Benedict’s, Tollens’

Orange —-> green

Deep blue solution —-> red precipitate

Deep blue solution —-> red precipitate

Colourless solution —-> Silver mirror

Aldehydes react with Benedict’s, Fehling’s and Tollens’, ketones do not

Carbonyls with CH3CO react with iodine to for triiodomethane - a yellow precipitate

COCH3 + 3I2 + 4OH- ——> RCOO- + CHI3 + 3I- + 3H20

An orange precipitate forms if a carbonyl is present
The precipitate can be purified by re-crystallisation
Each different carbonyl give a crystal with a different melting point
If the melting points are measured and compared to a table of known values, the compound can be identified

In aqueous alkaline solution containing potassium cyanide

CH3CH2CHO + HCN ----> CH3CH3CH(OH)CN

CH3COCH2CH3 + HCN ----> CH3C(CN)(OH)CH2CH3

Nucleophilic addition

The hydrogen atom attaches to the oxygen of the carbonyl and a cyanide group attaches to the carbon of the carbonyl group

Two , and an intermediate is formed

The arrangement of the two atoms or groups attached to the C=O is planar, so the cyanide ion can attack from above or below. Creates a chiral carbon, but with a equal amounts of dextrorotatory and laevorotatory enantiomers, no optical activity.

Formic acid

Evenly

They have distinctive smells and sour tastes

Very high

They have three polar bonds in the carboxylic acid group which give them strong intermolecular forces and hydrogen bonding

The longer the chain, the higher the boiling point because London forces increase

In the absence of a solvent, two molecules hydrogen bond with one another

Shorter chain ones, as they can form hydrogen bonds with water

Solubility decreases with increasing chain length

Oxidation and hydrolysis

Acidified potassium dichromate (VI) and reflux

CH3CH2CH2OH + 2[O] ----> CH3CH2COOH + H20

CH3CH2CHO + [O] ----> CH3CH2COOH

Nitriles and organic compounds containing CN group

Reflux with either a dilute acid or aqueous alkali

CH3CH2CN + H+ + 2H2O ----> CH3CH2COOH + NH4+

CH3CH2CH2CN + OH- + H2O ----> CH3CH2CH2COO- + NH3
Butanoate ion then converted into acid by adding dilute acid:
CH3CH2CH2COO- + H+ ----> CH3CH2CH2COOH

Reduction
Neutralisation
Halogenation
Esterification

A carboxylate salt

Lithium aluminium hydride

CH3COOH + NaOH ----> CH3COONa + H2O

Acyl chloride

Phosphorus (V) chloride and anhydrous conditions

Because both the reagent and the acyl chloride react vigorously with water

CH3CH2COOH + PCl5 ----> CH3CH2COCl + POCl3 + HCl

Alcohol and a small amount of acid catalyst, often conc H2SO4

HCOOH + CH3CH2OH HCOOCH2CH3 + H2O

RCOCl

Nucleophillic attack, as the carbon is joined to two electronegative atoms, so is electron deficient

Vigorously, forming a carboxylic acid and releasing hydrogen chloride gas, appearing as misty fumes

CH3COCl + H2O ----> CH3COOH + HCl

They readily react with ethanol to form ab ester and hydrogen chloride gas

CH3COCl + CH3CH2OH ----> CH3COOCH2CH3 + HCl

In two steps, an NH2 group joins with the carbonyl group to produce an amide as well as ammonium chloride

CH3COCl + 2NH3 ----> CH3CONH2 + NH4Cl

One H form the amine react with Cl to form HCl and the rest of the compound is attached to the carbonyl group

CH3COCl + CH3NH2 ----> CH3CONHCH3 + HCl

There is no H to react with the Cl to form HCl

Colourless liquids with low melting and boiling points, insoluble in water, no hydrogen bonding. Generally pleasant smell.

Hydrolysis in acidic solution and in alkaline solution

CH3COOCH2CH3 + H2O CH3COOH + CH3CH2OH

CH3CH3COOCH3 +NaOH ---> CH3CH2COO- + Na+ + CH3OH

Alkaline hydrolysis of esters to form an alcohol and a stearate, commonly used in soaps

Each time two monomer molecules join together, another small molecule is formed
Usually two different monomers react together

Often water

Through condensation polymerisation

A diol and a dicarboxylic acid