Topic 17.6 Organic Structures

Making something new form what already exists.

Put an outline of all the reactions you need to know.

1) Reacting a halogenoalkane with a cyanide ion (nucleophilic substitution). 2) Carbonyl compound with HCN (nucleophilic addition). 3) Alkylation of benzene (electrophilic subsitutuion).

-Organometallic compound. -General formula: RMgX (formed from halogenoalkane RX + Mg). -Magnesium is covalently bonded to both the alkyl group and the halogen. -Unstable and react with water, so prepared immediately before using solvent of dry ether. -RBr + Mg –> RMgBr -After its prepared, the second reagent is added……..

In Grignard reagent, the carbon is bonded to a much less electronegative element, Mg, so the carbon becomes polarised ….

1) With carbon dioxide: RMgBr –> RCOOH carboxylic acid 2) With methanal: RMgBr –> RCH2OH primary alcohol 3) With an aldehyde R’CHO: RMgBr –> RR’CHO secondary alcohol 4) With a ketone R’COR’’: RMgBr –> RR’R’‘COH tertiary alcohol.

Step 1: Formation of Grignard reagents (CH3)2CHCH2Br + Mg –> (CH3)CHCH2MgBr Step 2: Reaction with chosen reagent (CH3)2CHCH2MgBr + CO2 –> (CH3)2CHCH2COOMg Step 3: Hydrolysis using a dilute acid (CH3)2CHCH2COOMgBr + H2O –> (CH2)2CHCH2COOH + Mg(OH)Br The inorganic product of step 3 will react with the dilute acid.

Propan-1-ol (CH3CH2CH2OH) is a primary alcohol.

Pentan-2-ol (CH3CH(OH)CH2CH2CH3) is a secondary alcohol.

2-Methylpropan-2-ol ((CH3)3COH) is a tertiary alcohol.

-Reaction of methyl ketones or methyl secondary alcohols with iodine and sodium hydroxide forms a yellow precipitate of triiodomethane (iodoform) and a carboxylate salt with one fewer carbon atoms.

Eg. You are told to wear safety goggles when using acid because of the harm it could do if it got into eyes. –> The hazard exists because hydrochloric acid is corrosive. –> The risk is that hydrochloric acid may get into your eyes and cause harm.

-Some reactions are volatile, and there is a risk they will escape from the reaction during the heating process. -To prevent this from happening, heat in a flask fitted with reflux condenser. -All the vapours rising from the mixture during heating enter the condenser and change back into liquids and return to the flask so unreacted compounds can react.

-Obtain a liquid product from a reaction mixture that has a boiling temperature much lower than the other substances.

-Technique used to separate an insoluble liquid from an aqueous solution. -It involves passing steam into a mixture that contains an aqueous solution and a liquid that forms a separate layer.

Uses same apparatus as simple distillation, but with a fractionating column filled with glass beads which acts as surfaces of which the vapour leaving the column can condense. -Takes longer than simple distillation. -Best used when the difference in boiling temperatures is small, and when there are several compounds to be separated from a mixture.

1) Place reaction mixture in a separating funnel, then add the chosen solvent- it should form a separate layer. 2) Place the stopper in and gently agitate the contents. 3) Allow the contents to settle into two layers. 4) Remove the stopper and open tap to allow the lower layer to drain into a flask.

Used to remove impurities from a solid or liquid. Can be water or an organic solvent.

Left in a warm place or in a desiccator with a soluble drying agent.

Buchner and Hirsch funnels are vacuumed filtered (under pressure).

-If the compound is a solid, then its melting temperature can be measured. -If it is liquid, then its boiling temperature can be measured.

There is a stationary phase and a mobile phase (each component of the mixture is attracted to both phases). -A component that is strongly attracted to the stationary phase but weakly attracted to the mobile phase will not travel very far up the paper. -A component that is weakly attracted to the stationary phase but weakly attracted to the mobile phase will travel a long way up the paper.