Chapter 26 Flashcards
What carbonyl functional group do both aldhydes and ketones contain?
C=O
In aldehydes, where is the carbonyl functional group found?
At the end of a carbon chain
In its structural formula, what is the aldehyde group written as?
CHO
In its structural formula, what is the ketone group written as?
CO
What is the name of the simplest aldehyde?
methanal
What is the structure of the simplest aldehyde?
HCHO
What is the name of the simplest ketone?
propanone
What is the structure of the simplest ketone?
CH₃COCH₃
What is the common name for propanone?
acetone
What is the common name for methanal?
formaldehyde
What is formaldehyde used for?
To preserve biological specimens
How do you represent an oxidising agent?
[O]
What are aldehydes oxidised to?
Carboxylic acids
What are the conditions needed to oxidise aldehydes?
1) reflux
2) acidified dichromate(VI) ions, Cr₂O₇²⁻/H⁺
- -> sodium or potassium dichromate(VI), K₂Cr₂O₇
- -> dilute sulfuric acid, H₂SO₄
Can ketones be oxidised?
No
Can aldehydes be oxidised?
Yes
What influences the reactivity of aldehydes + ketones?
The nature of the carbon-oxygen double bond?
What is the carbon-hydrogen double bond made up of?
1) σ-bond
2) π-bond
Is the C=C double bond in alkenes polar or non-polar?
non-polar
Is the C=O double bond in carbonyl compounds polar or non-polar?
polar
Why is the C=O double bond polar?
1) oxygen is more electronegative than carbon
2) electron density in the double bond lies closer to the oxygen atom
3) carbon end of the bond is more positive
3) oxygen end of the bond more negative
What type of reactions do aldehydes + ketones undergo?
nucleophilic addition
What type of reactions do alkenes undergo?
electrophilic addition
What is a nucleophile?
An atom (or group of atoms) which is attracted to an electron-defficient centre or atom, where it donates a pair of electrons to form a new covalent bond
What is a σ-bond?
A bond formed by the overlap of one orbital from each bonding atom, consisting of two electrons and with the electron density centred around a line directly between the nuclei of the two atoms
What is a π-bond?
A bond formed above and below the plane of the carbon and oxygen atoms, formed by the sideways overlap of p-orbitals
What is the reducing agent used to reduce aldehydes and ketones to alcohols?
sodium tetrahydridoborate(III), NaBH₄
What type of alcohols are aldehydes reduced to?
Primary alcohols
How do you represent the reducing agent in the reduction of organic compounds?
[H]
What type of alcohols are ketones reduced to?
Secondary alcohols
What type of reaction is carbonyl compounds with HCN?
addition reaction
What two substances are used to provide hydrogen cyanide in reactions?
1) sodium cyanide
2) sulfuric acid
Why can you not safely use hydrogen cyanide in an open laboratory?
It is an extremely poisonous liquid
Why is the reaction of carbonyl compounds with HCN very useful?
It provides a means of increasing the length of the carbon chain
What are the two functional groups formed from the reaction of an aldehyde with hydrogen cyanide?
1) hydroxyl group, -OH
2) nitrile group, C≡N
What does an addition to carbonyl groups usually consist of?
1) nucleophilic attack on the carbonyl group to form a negatively charged intermediate
2) protonation of the intermediate to form an alcohol
What is the nucleophile in NaBH₄?
the hydride ion, :H⁻
What is the mechanism for the reaction of a carbonyl compound with NaBH₄?
1) lone pair of e- from hydride ion, :H⁻ attracted + donated to 𝛿+ C-atom in aldehyde/ketone C=O double bond
2) dative covalent bond formed between hydride ion and C-atom of C=O double bond
3) π-bond in C=O double bond breaks by heterolytic fission, forming negatively charged intermediate
4) O-atom of intermediate donates lone pair of e- to H-atom in water molecule. Intermediate has been protonated to form alcohol
What is the mechanism for the reaction of a carbonyl compound with NaCN/H⁺?
1) lone pair of e- from cyanide ion, :CN⁻ attracted + donated to 𝛿+ C-atom in aldehyde/ketone C=O double bond –> dative covalent bond forms
2) π-bond in C=O double bond breaks by heterolytic fission, forming negatively charged intermediate
3) intermediate protonated by donating lone pair of e- to hydrogen ion, to form product
4) product is hydroxynitrile
What is used to detect the presence of the carbonyl functional group in both aldehydes + ketones?
2,4-dinitrophenylhydrazine (2,4-DNP)
What is produced when a carbonyl group is present in 2,4-DNP?
a yellow/orange precipitate
What is 2,4-DNP usually dissolved in?
methanol + sulfuric acid
Why is 2,4-DNP very hazardous?
Friction or a sudden blow can cause it to explode
How do you carry out the test for the carbonyl group in aldehydes + ketones?
1) add 5cm depth 2,4-DNP to clean test tube
2) use dropping pipette to add 3 drops of unknown compound + leave to stand
3) if no crystals form, add few drops of sulfuric acid
4) yellow/orange precipitate = aldehyde/ketone
What is used to detect the presence of the carbonyl functional group in aldehydes?
Tollens’ reagent
What is produced when a carbonyl group is present in Tollens’ reagent?
A silver mirror
How do you carry out the test for the carbonyl group in aldehydes?
1) pour 2cm depth of unknown solution into clean test tube
2) add equal volume of freshly prepared Tollens’ reagent
3) leave test tube to stand in beaker of warm water (around 50°) for 10-15 mins + observe whether a silver mirror is formed
How do you identify an aldehyde or ketone by melting point?
1) filter impure yellow/orange solid to separate solid precipitate from solution
2) recrystallise solid to produce pure sample of crystals
3) measure + record melting point of purified carbonyl compound
4) compare melting point to database/data table of melting points to identify original carbonyl compound
What is a carboxylic acid?
An organic acid which contains the carboxyl functional group
What does the carboxyl functional group contain?
1) carbonyl group
2) hydroxyl group
Why can carboxylic acids form hydrogen bonds with water molecules?
The C=O and O-H bonds in carboxylic acids are polar
What is the maximum number of carbon atoms a carboxylic acid can have to be soluble in water
4
What happens to the solubility as the number of carbon atoms in carboxylic acids increase?
Solubility decreases as the non-polar carbon chain has a greater effect on the overall polarity of the molecule
What are dicarboxylic acids?
Acids with two polar carboxyl groups to form hydrogen bonds
Are carboxylic acids strong or weak acids?
Weak acids
Do carboxylic acids fully or partially dissociate in water?
Partially
What type of reactions do carboxylic acids take place in?
1) redox reactions with metals
2) neutralisation reactions with metals
What do carboxylic acids react with metals in a redox reaction to form?
hydrogen gas + carboxylate salt
What do carboxylic acids react with metal oxides in a neutralisation reaction to form?
salt + water
What do carboxylic acids react with alkalis in a neutralisation reaction to form?
salt + water
What do carboxylic acids react with carbonates in a neutralisation reaction to form?
salt + carbon dioxide + water
How do you test for the carboxyl group?
Neutralise carboxylic acids with carbonates as carboxylic acids are the only common organic compounds sufficiently acidic to react with carbonates
What is a derivative of a carboxylic acid?
A compound that can be hydrolysed to form the parent carboxylic acid
How do you name an acyl chloride?
Remove the -oic acid suffix from the parent carboxylic acid and replace with -oyl chloride
How is an acid anhydride formed?
By the removal of water from two carboxylic acid molecules
What is esterification?
The reaction of an alcohol with a carboxylic acid to form an ester
What can esters be hydrolysed by?
1) aqueous acid
2) aqueous alkali
What is hydrolysis?
the chemical breakdown of a compound in the presence of water or in aqueous solution
How do you carry out acid hydrolysis?
heat ester under reflux with dilute aqueous acid
What happens in acid hydrolysis?
ester is broken down by water, with acid acting as catalyst
How do you carry out alkaline hydrolysis?
heat ester under reflux with aqueous hydroxide ions
How do you prepare acyl chlorides?
react the parent carboxylic acid with thionyl chloride, SOCl₂
What happens when water is added to an acyl chloride?
1) dense steamy hydrogen chloride fumes
2) carboxylic acid is formed
How can ammonia and amines act as nucleophiles?
by donating the lone pair of electrons on the nitrogen atom to an electron-deficient species
What happens when ammonia/amine is added to an acyl chloride?
forms an amide
ammonia + acyl chloride –>
primary amine
primary amine + acyl chloride –>
secondary amide
Are acid anhydrides more or less reactive than acyl chlorides?
less
