Chemistry - Organic

What is a disproportionation reaction

Where both oxidation and reduction take place .

Problems with Chlorine reacting with water in sunlight

The chlorine is regularly lost from water so has to be regularly topped up.

What are the properties of Catalytic Cracking?

Low temperature and normal pressure but with a zeolite catalyst to produce aromatic compounds with carbon rings

Equation for Catalytic converters?

2CO + 2NO → 2CO2 + N2

Equation for flue gas desulphurization?

CaO + SO2 → CaSO3

What are the nucleophiles used in nucleophilic substitution? Which ones have the lone pair and which nucleophile with no negative charge?

CN, NH3, OH, the C N and the O, NH3 has no negative charge

What conditions are needed for FRS?

alkanes and halogens react under UV light to form very reactive free radicals in the process.

Why are halogenoalkanes more reactive than normal alkanes?

The carbon halogen bond becomes a dipole. Reactivity of the halogenoalkanes increases as the bond gets weaker down the group.

Why are the formation of major products favoured than minor products?

Major products are made from a more stable carbocation. This stability arises from a greater positive inductive effect.

How to identify alkenes?

Use bromine water, if a double bond is present the solution will go from orange-brown to colourless.

How are branched chain polymers formed?

High pressures and temperatures produce branched chain polymers with weak intermolecular forces

How are straight chain polymers formed?

Low temperatures and pressures produce these with strong intermolecular forces.

What are some properties of polymers that make it good for the production of plastics?

They have multiple strong, non polar covalent bonds.

What is observed when an alcohol is oxidised?

Colour change from orange to green

Properties of thermal cracking

High Temperature and pressure to produce more alkenes than alkanes

What does reacting an acyl chloride/acid anhydride with water make?

Carboxylic acid + HCl/Carboxylic acid

What does reacting an acyl chloride/acid anhydride with alcohol make?

Ester + HCl/Carboxylic acid

What does reacting an acyl chloride/acid anhydride with Ammonia make?

Amide + HCl/Carboxylic Acid

What does reacting an acyl chloride/acid anhydride with a primary amine make?

N-substituted amide + HCl/Carboxylic acid

What is stereoisomerism?

Two molecules with the same molecular and structural formula but the atoms are arranged differently in 3D space

Equation for the decomposition of ozone.

cl. + o3 → clo. + o2

clo. + o3 → 2o2 + cl.

Why is FG desulphurization used?

To remove SO2 by neutralisation from waste gases which are produced during combustion processes.

Why are catalytic converters used?

They remove CO, NO and unburned hydrocarbons. They are lined with a platinum catalyst to increase surface area.

How can you distinguish acyl chlorides?

Add silver nitrate solution and white ppt of silver chloride should form

How does the shape of an organic molecule affect bp and mp?

Straight chain alkanes have a higher bp and mp because a greater surface area is in contanct with many more molecules so many more vdw forces can be made.

Why is heating under reflux used?

The reaction can run at the solvents boiling point for longer to ensure the reaction goes to completion, ensuring a higher yield without losing vapour materials.

Why is KCN used instead of HCN in cyanide mechanisms?

HCN is toxic and hard to store as a gas. KCN will completely ionise and HCN only partially ionises.

How are racemic mixtures produced?

The planar carbonyl group (C=O) means that the nucleophile can attack from either side with equal probability. The aldehyde/ketone must also be unsymmetrical.

Why are acid anyhdrides preferred to acyl chlorides?

Cheaper, less corrosive, no corrosive hcl produced, less exothermic

How is biodiesel formed?

When a triglyceride ester reacts with methanol forming 3 methyl-esters and glycerol (propane-1,2,3-triol). This reaction requires a strong base catalyst of NaOH.

What happens in acidic hydrolysis?

Acidic conditions and a H+ ion catalyst so it is a slow process. It happens in equilibrium so yeild of the alcohol and carboxylic acid are always low.

What catalyst is used to form esters from alcohols and carboxylic acids?

concentrated sulfuric acid

Test for aldehydes with fehlings solution

Changes colour from blue to a red ppt.

What happens in basic hydrolysis?

Ester will react with a base (NaOH) forming an alcohol and a carboxylate salt. The reaction goes to completion so has a higher percentage yield. You can regenerate the carboxylic acid by reacting the salt with a strong acid.

How does infrared spectroscopy work?

The bond that joins a pair of atoms is always vibrating. The stronger bonds vibrate faster at a higher frequency. This bond, will absorb a frequency of IR radiation equal to the natural frequency of the bond. The radiation emerged can be passed through an instrument where it plots a graph of intensity against frequency. The dips represent frequencies of specific bonds in the sample being absorbed.

How do you test for an alcohol?

Add a small peice of sodium metal to the test tube containing the alcohol. The gas released can be tested against a lit split which pops if hydrogen is released.

Add acidified potassium dichromate, primary and secondary alcohols will change from orange dichromate ions to green chromium ions. Tertiary alcohols experience no change

Test for an aldehyde?

Warm with fehlings solution in a hot water bah for a few minutes, a brick red ppt forms if an aldehyde is present

Add silver nitrate, dilute sodium hydroxide and dilute ammonia to a test tube. Add the aldehyde and warm for a few minutes. A silver mirror forms on the edges of the test tube if an aldehyde is present.

Test for a halogenoalkane?

Sodium hydroxide solution warmed then add silver nitrate and dilute nitric acid. Add the haloalkane and a silver halide ppt should form.

How can a PVC be made flexible?

Adding a plasticiser

What is the structure of the benzene molecule?

A planar hexagonal molecule with 6 carbon atoms. It has a 120 degree bond angle with all C-C bonds equal in length.

What is the bonding in the benzene molecule?

Each Carbon makes three covalent bonds, 2 to carbon and 1 to hydrogen. Delocalised electrons in the p orbital overlap to form an electron ring above and below the plane of the molecule.

What was the original structure of benzene?

A hexagonal ring with alternating double and single bonds.

Why is the new model of benzene more thermodynamically stable than the old structure of benzene?

It has a delocalised electron orbital

What is the difference in stability between benzene and the hypothetical cyclohexatriene?

Benzene is less exothermic and more stable by 152 kJ mol^-1

What is the order of the bonds of increasing bond length in cyclohexatriene and benzene?

c=c, c-c bond in benzene, normal c-c bond

What is the name for aromatic compounds that contain a benzene ring?

Arenes

What reactions does benzene undergo?

Electrophilic substitution

In nitration of benzene, give the reagents needed to produce the electrophile NO2+

Concentrated H2SO4 and HNO3

How is the electrophile NO2+ generated?

H2SO4 + HNO3 → HSO4- + H2O + NO2+

Which reagent in making the NO2+ electrophile is the base?

HNO3 as it accepts the H+ proton

What is formed in the acylation of benzene?

A phenyl ketone

What is the electrophile in the acylation of benzene and how is it formed?

RCO+, formed by reacting an acyl chloride/anhydride with aluminium chloride which is the catalyst.

What is the equation to form the RCO+ electrophile?

AlCl3 + RCOCl → AlCl4- + RCO+

Why is aluminium chloride a good choice for forming the RCO+ electrophile?

The substance is polar covalent so the distorted cloud comes from the aluminium being small and having a high positive charge density which means it polarises the electron cloud around the chloride ion.

How is the catalyst regenerated from AlCl4-?

AlCl4- + H+ → AlCl3 + HCl

In what complexes does cis(Z) - trans (E) isomerism occur?

Octahedral and square planar

What would a cis (Z) isomer look like?

2 ligands which are next to each other

What would a trans (E) isomer look like?

2 ligands opposite to each other

In what complexes does optical isomerism occur?

Octahedral complexes

Give an example of a linear complex.

[Ag(NH3)2]+

Give an example of a square planar complex.

[PtCl4]2-

Give an example of a tetrahedral complex.

[CuCl4]2-

Give an example of an octahedral complex.

[Cu(H2O)6]2+

Why does NMR sepctroscopy work?

Different bond environments absorb different amounts of energy, therefore they show as different peaks on a spectrum.

Why is TMS used in NMR spectroscopy?

It is added along with the organic molecule to be used as a standard. It will show as one peak at 0ppm on the x axis. It is inert and non-toxic and can be removed from the sample easily as it has a low boiling point.

In what solvent should samples that are being analysed in Proton NMR be dissolved in, and why are these solvents used?

CCl4 or CDCl4 as they are non polar and they do not contain any hydrogen atoms so will not produce any peaks on the spectrum.