Chapter 26: Carbonyls and Carboxylic Acids

Question 1

What is the functional group that aldehydes and ketones share?

Answer 1

Carbonyl

Question 2

Where is the carbonyl group located on aldehydes and ketones?

Answer 2

Aldehydes - end of carbon chain

Ketones - middle of carbon chain

Question 3

Why can ketones not undergo oxidation reactions?

Answer 3

Lack of reactivity

Question 4

What can aldehydes be oxidised to? How do you oxidise aldehydes?

Answer 4

Oxidised to CARBOXYLIC ACIDS when refluxed with acidified sodium/potassium dichromate and dilute sulfuric acid.

Question 5

Why are the properties of a C=O bond different to a C=C bond?

Answer 5

C=O is polar and therefore attract nucleophiles towards the slightly positive carbon .

Question 6

What type of addition reaction do Carbonyl compounds undergo vs alkenes?

Answer 6

Alkenes - ELECTROPHILIC addition

Carbonyl - NUCLEOPHILIC addition

Question 7

What does reacting aldehydes and ketones with sodium tetrahydridoborate do? (NaBH4)

Answer 7

NaBH4 acts as a reducing agent and reduces them to alcohols.

Question 8

What is produced when an aldehyde and ketone are reacted with NaBH4?

Answer 8

Aldehyde - PRIMARY alcohol

Ketone - SECONDARY alcohol

Question 9

When writing the equation for reduction with NaBH4 with aldehyde/ketone what should you remember?

Answer 9

+2[H] and then NaBH4/H20 over the arrow

Question 10

What does reacting carbonyl compounds with HCN (hydrogen cyanide) do?

Answer 10

Increases the length of the carbon chain.

Question 11

What is the type of reaction between HCN and a carbonyl compound?

Answer 11

Addition

Question 12

What must you remember when carrying out a reaction with HCN?

Answer 12

Fume cupboard because HCN is an extremely poisonous liquid that boils slightly above room temperature.

Question 13

List the step of the mechanism between NaBH4 and a carbonyl.

Answer 13

• Hydride ion from NaBH4 acts as a nucleophile
• Dative covalent bond between carbon and hydride ion
• Pi bond of C=O breaks through heterolytic fission
• Oxygen donates electrons to hydrogen of water molecule (dative covalent bond)
• Intermediate has been protonated to form an alcohol + OH-

Question 14

What is the name of the product form HCN?

Answer 14

Hydroxynitrile

Question 15

What reagent do you use to detect the Carbonyl group?

Answer 15

2,4 DNP (Brady’s Reagent)

Question 16

What reagent do you use to distinguish between aldehydes and ketones?

Answer 16

Tollen’s Reagent

Question 17

Describe how you use 2,4 DNP to detect the carbonyl group.

Answer 17

• Add 2,4 DNP to sample

- Forming of yellow/orange precipitate means presence of ketone/aldehyde.

Question 18

Describe how Tollen’s Reagent can be used to distinguish between ketones and aldehydes.

Answer 18

Ketones cannot be oxidised whereas aldehydes can.
Tollen’s reagent is a solution of SILVER NITRATE in aq ammonia.
Silver IONS(ag+) act as oxidising agents and become reduced to SILVER (ag) when an aldehyde is present to form a SILVER MIRROR.

Question 19

Give the half equation of silver ions being reduced to silver in the Tollen’s reagent.

Answer 19

Ag+(aq) + e- —-> Ag(s)

Question 20

What functional groups do carboxylic acids have?

Answer 20

Carbonyl and Hydroxyl

Question 21

What bonds can carboxylic acids do and why?

Answer 21

Hydrogen bonding due to the polar OH bonds with lone pairs of oxygen.

Question 22

What property does the hydrogen bonding give carboxylic acids?

Answer 22

Solubility

but with increasing carbon chain, the solubility decreases.

Question 23

Carboxylic acids are WEAK acids. What does this mean?

Answer 23

Hydrogen atoms partially dissociate.

HCOOH (aq) —> H+ (aq) + HCOO-(aq)

Question 24

What kind of reactions do Carboxylic Acids undergo with metals?

Answer 24

REDOX

forming a carboxylate salt and HYDROGEN GAS

Question 25

What kind of reaction do Carboxylic Acids undergo with bases (alkalis, metal oxides and carbonates)?

Answer 25

NEUTRALISATION
Alkalis&Metal oxides form carboxylate salt and WATER
Carbonates form carboxylate salt and WATER AND CO2

Question 26

What are the 4 derivatives of carboxylic acids?

Answer 26

esters, acyl chlorides, acid anhydrides, amides

Question 27

What are derivatives?

Answer 27

when compounds can be hydrolysed to form their parent compound (CA).

Question 28

How are esters formed?

Answer 28

CA warmed with alcohol with sulfuric acid catalyst - esterification

Question 29

How are esters named?

Answer 29

ALCOHOL -yl + CARBOXYLIC ACID -oate

Question 30

How are Acyl chlorides formed?

Answer 30

CA reacted with THIONYL CHLORIDE (SOCl2) to form acyl chloride + so2 + HCl (FUME CUPBOARD NEEDED!)

Question 31

How are acyl chlorides named?

Answer 31

-oyl chloride

Question 32

What are the 2 methods of hydrolysing esters?

Answer 32

1. reflux with dilute aqueous acid

2. reflux with aqueous alkali

Question 33

How does refluxing with dilute aqueous acid cause hydrolysis of esters?

Answer 33

dilute aq - water for hydrolysis

acid acts as a catalyst

Question 34

What is formed form alkaline hydrolysis of esters?

Answer 34

carboxylate ion and alcohol

Question 35

Why are acyl chlorides useful in organic synthesis?

Answer 35

They are very reactive and can easily be converted to carboxylic acid derivatives.

Question 36

How do you form an ester with an acyl chloride?

Answer 36

React with alcohol.

Hydrogen chloride also formed.

Question 37

With which alcohol can only acyl chlorides be reacted with in order to form an ester and why?

Answer 37

PHENOL
because cannot form ester with carboxylic acids as they’re not reactive enough.
Form phenyl ester + hydrogen chloride

Question 38

What does a reaction of acyl chloride and water produce?

Answer 38

Carboxylic acid and hydrogen chloride.

Question 39

What does a reaction of acyl chloride with ammonia and amine produce?

Answer 39

Ammonia - primary amide

amine - secondary amide