Compounds Conataining The Carbonyl Group

Question 1

Physical properties of carbonyl compounds

Answer 1

Carbonyl group strongly polar so permanent dipole-dipole forces so boiling point higher than alkanes of similar length but lower than alcohols. Short chain aldehydes and ketones mix completely with water as H bonds form between the O in C=O and the H of the water. The longer the chain, the less soluble.

Question 2

How is addition of hydrogen cyanide made safer?

Answer 2

Use sodium or potassium cyanide followed by the addition of dilute HCl

Question 3

What is a common reducing agent for aldehydes and ketones?

Answer 3

Sodium tetrahydridoborate (NaBH4). Generates nucleophile H- with lone pair (hydride ion)

Question 4

Mechanism for reduction of carbonyl compounds (nucleophilic addition)

Answer 4

Arrow from lone pair of H- to delta+ C of C=O and arrow from double bond to O. Arrow from new lone pair on O- to H+ (from solvent) aldehydes form a primary alcohol. Ketones form a secondary alcohol. In equations [H] is used for reducing agent.

Question 5

How to name a carboxylic acid with a benzene ring

Answer 5

Suffix is carboxylic acid.

Question 6

Physical properties of carboxylic acids

Answer 6

Short chain ones are completely soluble in water as hydrogen bonds form between O on water and H on OH and between H on water and O on C=O. The acids also for H bonds with each other (C=O to OH) so have higher meting point than alkanes if similar mass.

Question 7

How are esters derived?

Answer 7

They are derived from carboxylic acids where the H from the OH is replaced by a hydrocarbon group. This is through reacting them with alcohols (by product of water). The reaction is reversible and sped up using a strong acid catalyst.

Question 8

Uses of esters

Answer 8

Flavourings and perfumes. Solvents and plasticisers. Fats and oils are esters with longer carbon chains.

Question 9

Describe a carboxylate ion

Answer 9

Formed when the H from the OH is lost from a carboxylic acid. The negative charge is shared over the whole carboxylate group (COO-). This délocalisation makes the ion more stable.

Question 10

How can an ester be split up?

Answer 10

Through hydrolysis. It reacts with water to from the original carboxylic acid and alcohol. The water acts as a weak nucleophile. It is a reversible reaction and sped up using a strong acid catalyst. Can happen at room temperature.

Question 11

What happens when a base is used as a catalyst for hydrolysis of esters?

Answer 11

The reaction isn’t reversible so there is more product in the mixture. The salt of the original carboxylic acid is produced rather than the acid itself. Water is also produced.

Question 12

What is the arrangement of oils and fats?

Answer 12

They contain three molecules of long chain carboxylic acids called fatty acids. Fats and oils are based on glycerol so are referred to as triglycerides.

Question 13

What is glycerol?

Answer 13

Propane- 123-triol

Question 14

What does hydrolysis of fats in acid conditions produce?

Answer 14

Mixture of glycerol and the components of fatty acids

Question 15

What does hydrolysis of fats by boiling with NaOH produce?

Answer 15

Glycerol and mixture of sodium salts (soaps) of the three acids which formed part of the ester.

Question 16

How do soaps work?

Answer 16

The sodium salts dissociate. The RCOO- has two distinct ends. One is a long, non-polar hydrocarbon chain which will mix with grease. The other is the COO- group which is polar and ionic so mixes with water. It allows grease and water to mix.

Question 17

Uses of glycerol

Answer 17

Used in pharmaceutical and cosmetic preparations (attracts water so stops them from drying out). Solvent in many medicines. Food colourings. Plasticiser.

Question 18

What is acylation?

Answer 18

Process by which the acyl group (RC=O) is introduced into another molecule.

Question 19

What is an acid derivative?

Answer 19

An organic compound related to a carboxylic acid with the general formula of RCOZ and contain an acyl group.

Question 20

What is the order or reactivity for reactions with acyl chlorides and acid anhydrides?

Answer 20

Primary amine > ammonia > alcohol > water

Question 21

What are the products of addition-elimination reactions for each reactant?

Answer 21

Amine to N-substituted amide. Ammonia to amide. Alcohol to ester. Water to carboxylic acid.

Question 22

General mechanism for addition-elimination reactions

Answer 22

Arrow from lone pair of nucleophile to delta+ carbon of C=O and arrow from double bond to O of C=O. Arrow from new lone pair on O- to new C-O bond and arrow from C-Cl bond to Cl. Arrow from Nu-H bond to Nu+. Forms HCl.

Question 23

Why is ethanoic anhydride preferred to ethanoyl chloride as an acylating agent?

Answer 23

Cheaper, less corrosive, not as reactive with water, by-product safer (ethanoic acid compared to HCl)

Question 24

Why is the minimum volume of hot water added in recrystallisation of aspirin?

Answer 24

To obtain a saturated solution, to increase yield, enable crystallisation on cooling.

Question 25

Why is the solution filtered hot in recrystallisation of aspirin?

Answer 25

To remove insoluble impurities and prevent crystals forming during filtration.

Question 26

Why is the filtrate cooled in ice in recrystallisation of aspirin?

Answer 26

To increase the amount of crystals that are formed.

Question 27

Why are the crystals washed in cold water in recrystallisation of aspirin?

Answer 27

To remove soluble impurities. Using hot water would dissolve some of the crystals.

Question 28

How to determine the melting point of aspirin

Answer 28

Heat melting point tube in an oil bath. Heat slowly near the melting point.

Question 29

What is the process called to produce biodiesel from vegetable oils?

Answer 29

Transesterification

Question 30

Mechanism for nucleophilic addition with HCN

Answer 30

Arrow from lone pair on CN- to δ+ C of C=O and arrow from C=O bond to O. Arrow from lone pair of new O- to H+. Forms hydroxynitrile.

Question 31

How is biodiesel made?

Answer 31

React vegetable oils (like rape seed oil) with methanol with strong alkali catalyst. Forms a mixture of methyl esters of long chain carboxylic acids which is the biodiesel.

Question 32

Apparatus for filtration under reduced pressure

Answer 32

Conical flask with side arm which goes to a tube connected to tap or vacuum pump (tube doesn’t always need to be shown). Büchner funnel (more rectangular than Y-shaped) with filter paper in with air tight connection to flask. No cut off connections.

Question 33

How to purify an organic liquid

Answer 33

Put distillate of impure product in separating funnel. Wash product by adding either sodium hydrogencarbonate solution or saturated NaCl solution. Allow layers to separate in funnel and run tap to discard aqueous layer. Run organic layer in clean dry conical flask and add spatulas of drying agent. Carefully decant liquid into distillation flask and distill to collect pure product.

Question 34

Why is the separating funnel inverted periodically and the tap opened?

Answer 34

To release the pressure due to CO2 being formed from the reaction of left over acid with sodium hydrogencarbonate.

Question 35

Why would saturated NaCl solution be used to wash the impure organic liquid?

Answer 35

It helps separate the organic layer from the aqueous layer.

Question 36

What are the criteria for a good drying agent for an organic liquid?

Answer 36

Be insoluble in the organic liquid. Not react with the organic liquid.