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OCR A Level Chemistry > Chapter 26 - Carbonyls and Carboxylic acids > Flashcards

Chapter 26 - Carbonyls and Carboxylic acids Flashcards

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1
Q

What is the carbonyl functional group?

A

C=O

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2
Q

What is the difference between an aldehyde and a ketone?

A

Aldehyde group written as CHO, attached to end of carbon chain
Ketone group written as CO, attached to two carbon atoms in the carbon chain

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3
Q

What oxidation reactions do aldehydes and ketones undergo?

A

Aldehydes oxidised to carboxylic acids when refluxed with acidified K2Cr2O7.
Ketones do not undergo oxidation reactions

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4
Q

Why do aldehydes and ketones react with nucleophiles?

A

Due to the polarity of the C=O bond (O is more electronegative, making it slightly negative).

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5
Q

What is a nucleophile?

A

An electron donor

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6
Q

How is an aldehyde reduced, what is the product?

A

Aldehydes are reduced to primary alcohols by NaBH4
NUCLEOPHILIC ADDITION

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7
Q

How is a ketone reduced, what is the product?

A

Ketones are reduced to secondary alcohols by NaBH4
NUCLEOPHILIC ADDITION

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8
Q

How do carbonyl compounds react with HCN?

A

HCN adds across the C=O bond to form a hydroxynitrile
NUCLEOPHILIC ADDITION

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9
Q

What happens in nucleophilic addition?

A

Nucleophile attracted to delta positive C atom, and a dative covalent bond is formed.
The pi bond in the C=O double bond breaks by heterolytic fission to form a negatively charge intermediate. The oxygen atom of the intermediate donates a lone pair of electrons to a H atom in a water molecule. Intermediate has been protonated to form an alcohol.

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10
Q

What is the mechanism for the reaction with NaCN/H+?

A

Lone pair from CN- ion forms dative covalent bond with the delta positive C atom. Pi bond in C=O double bond breaks by heterolytic fission to form negatively charged intermediate. Intermediate protonated by donating lone pair to H+ ion to form hydroxynitrile

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11
Q

How can you test for the presence of the carbonyl functional group in both aldehydes and ketones?

A

2,4-DNP
In the presence of a carbonyl group, a yellow/orange precipitate forms

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12
Q

What test can you use to distinguish between aldehydes and ketones?

A

Use Tollen’s reagent - solution of silver nitrate in aqueous ammonia. In presence of aldehyde group, a silver mirror is produced

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13
Q

Why does Tollen’s create a silver mirror for aldehydes/not react with ketones?

A

Silver ions reduced to silver as aldehyde is oxidised to a carboxylic acid.
Ketones cannot be oxidised

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14
Q

How can the precipitate formed by the 2,4 - DNP test be analysed to identify the carbonyl compound?

A

Impure solid filtered to separate solid precip from solution. Solid then recrystallised to produce a pure sample of crystals. The melting point is then measured and recorded and compared to a database

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15
Q

What is the solubility of the carboxylic acids?

A

C=O and O-H bonds are polar allowing carboxylic acids to form hydrogen bonds with water molecules. Carboxylic acids with up to 4 C atoms are soluble in water - as chain length increases, solubility decreases

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16
Q

What is the strength of carboxylic acids?

A

They are weak acids, which only partially dissociate

17
Q

How do carboxylic acids react with metals, what type of reaction is this?

A

Form hydrogen gas and carboxylate salt
REDOX

18
Q

How do carboxylic acids react with metal oxides, alkalis and carbonates - what type of reaction are these?

A

Metal oxides and alkalis - salt + water
Carbonates - salt + water + carbon dioxide
NEUTRALISATION

19
Q

How can you test for the carboxyl group?

A

Only common organic compound sufficiently acidic to react with carbonates (produce CO2)

20
Q

What is an ester’s functional group?

A

COO

21
Q

What is an acyl chloride’s functional group?

A

COCl

22
Q

What is an acid anhydride’s functional group?

A

(CO)2O

23
Q

What happens in esterification?

A

Reaction of an alcohol with a carboxylic acid to form an ester
Alcohol warmed with carboxylic acid and a small amount of conc H2SO4

24
Q

What is hydrolysis?

A

The chemical breakdown of a compound in the presence of water or in aqueous solution

25
Q

What happens in acid hydrolysis?

A

Ester heated under reflux with dilute aq acid. Ester broken down by water, with acid acting as a catalyst. REVERSIBLE REACTION

26
Q

What are the products of acid hydrolysis?

A

A carboxylic acid and a base

27
Q

What happens in alkaline hydrolysis?

A

Ester heated under reflux with aqueous hydroxide ions. IRREVERSIBLE REACTION

28
Q

What are the products of alkaline hydrolysis?

A

A carboxylate ion and an alcohol. Salt can form if NaOH used

29
Q

How can acyl chlorides be prepared?

A

Reaction between carboxylic acid and thionyl chloride, SOCl2. (Other products are SO2 and HCl)

30
Q

What happens when an acyl chloride reacts with an alcohol?

A

Ester formed + HCl

31
Q

What happens when an acyl chloride reacts with water?

A

Violent reaction takes place with evolution of dense steamy HCl fumes. Carboxylic acid formed

32
Q

What happens when an acyl chloride reacts with ammonia or amines?

A

Ammonia and amines acts as nucleophiles to form amides.
Ammonia + acyl chloride = primary amide
Primary amide + acyl chloride = secondary amide

33
Q

What happens when an acyl chloride reacts with phenol?

A

Forms an ester
(carboxylic acids are unable to do this as they are not reactive enough)

34
Q

How are the reactions of acid anhydrides similar/different to acyl chlorides?

A

React in similar way with alcohols, phenols, water, ammonia and amines
but less reactive than acyl chlorides

35
Q

How are acid anhydrides formed?

A

removal of water from two carboxylic acid molecules

OCR A Level Chemistry (29 decks)

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