Module 6 - [ch26] (carbonyls and carboxylic acids)

Question 1

What is the functional group of aldehydes and ketones and what distinguishes one from another?

Answer 1

carbonyl functional group
C=O

the position of the C=O differs

Question 2

Where are the functional group of carbonyls, aldehydes and ketones found?

Answer 2

aldehydes - the carbonyl functional group is found at the end of a carbon chain

ketone - the functional group is joined to two carbon atoms in the carbon chain

Question 3

what are aldehydes oxidised to?

Answer 3

carboxylic acids

Question 4

conditions for oxidation of an aldehyde

Answer 4

refluxed with acidified potassium dichromate

dichromate solution turns from orange to green

Question 5

What is the difference in the way carbonyls react and alkenes react

Answer 5

alkenes - C=C non-polar bond
carbonyls - C=O polar bond

carbonyls react with some nucleophiles by nucleophilic addition

alkenes react with electrophiles by electrophilic addition

Question 6

Why is the C=O bond polar

Answer 6

Oxygen is more electronegative than carbon
the electron density lies closer to the oxygen atom making the oxygen end slightly negative and the carbon end delta positive

Question 7

What is NaBH4 used as reacting with carbonyl compounds

Answer 7

reducing agent

Question 8

what are aldehydes and ketones reduced to

Answer 8

aldehydes - primary alcohols
ketones - secondary alcohols

Question 9

conditions for the reduction of carbonyl compounds

Answer 9

NaBH4
gently warmed with reducing agent in aqueous solution

+ 2[H] (reducing agent e.g)

Question 10

what type of reaction is that of carbonyl compounds with HCN

Answer 10

addition reaction

Question 11

describe hydrogen cyanide

Answer 11

colourless, extremely poisonous liquid

Question 12

advantages of reaction of carbonyls with HCN

Answer 12

increases the chain length

Question 13

aldehyde + HCN –H2SO4/H2O–>

Answer 13

hydroxynitrile

Question 14

what type of reaction is the one by which aldehydes and ketones react to form alcohols

Answer 14

nucleophilic addition

Question 15

describe mechanism for reaction of a carbonyl with NaBH4

Answer 15

lone pair on hydride ion (from NaBH4) attracted to delta plus charge on carbon atom
dative covalent bond formed between hydride ion and carbon atom
Pi bond breaks apart by heterolytic fission making oxygen negative (intermediate)
Lone pair on oxygen donated to a delta positive hydrogen in a water molecule
= alcohol + OH-

Question 16

describe mechanism for reaction of a carbonyl with HCN

Answer 16

lone pair of electrons on cyanide ion attacks electron deficient carbon atom
dative covalent bond formed
Pi bond breaks by heterolytic fission
Oxygen donates lone pair to hydrogen ion
hydroxynitrile formed

Question 17

where is the negative charge on a CN

Answer 17

on the carbon atom

-:CN

Question 18

What is used to detect the presence the presence of the carbonyl functional group?

Answer 18

brady’s reagent
2,4 DNP
2,4 dinitrophenylhydrazine

Question 19

what is the positive test for the carbonyl functional group

Answer 19

2,4 DNP
yellow/orange precipitate forms

Question 20

What is the issue with using 2,4 DNP to identify organic compounds

how is this overcome

Answer 20

gives a positive result for both aldehydes and ketones
further tests need to be carried out to distinguish between the two

taking melting point of precipitate, compare to database, distinguishes aldehydes from ketones

Question 21

What is Tollen’s reagent? What is one of it’s properties?

Answer 21

a solution of silver nitrate in aqueous ammonia
silver complex ions in colourless solution

has a short shelf-life so must be made up immediately before carrying out a test

Question 22

How do you test for an aldehyde

Answer 22

tollen’s reagent
gently warm (water bath 50 degrees)
produces a silver mirror

Question 23

How do you prepare tollen’s reagent

Answer 23

Add silver nitrate in a test tube AgNO3(Aq)
Add aqueous sodium hydroxide NaOH until a brown precipitate of silver oxide Ag2O formed
Add dilute ammonia solution until precipitate dissolves to form clear and colourless solution

Question 24

what is an carboxylic acid

Answer 24

an organic acid with the carboxyl functional group

Question 25

Which carboxylic acids are soluble in water

Answer 25

carboxylic acids with up to 4 carbon atoms

Question 26

Why are carboxylic acids soluble in water

Answer 26

C=O O-H polar bonds which can form hydrogen bonds with water molecules

Question 27

How does solubility of carboxylic acids change as chain length increases

Answer 27

solubility decreases as chain length gets longer, the non-polar carbon chain has a greater effect on the overall polarity of the molecule than the carboxyl group

Question 28

what are dicarboxylic acids

Answer 28

have two polar carboxyl groups solids at room temp and dissolve readily in water

Question 29

what type of acid are carboxylic acids

Answer 29

weak acids partially dissociates HCOOH <-> H+ HCOO-

Question 30

carboxylic acid + metal PRODUCTS

Answer 30

carboxylate salt + hydrogen gas

Question 31

give a general formula for carboxylic acid + metal

Answer 31

acid(COOH) + metal -> (negative acid ion)(metal positive ion) + H2(g)

Question 32

what type of reaction is that of a carboxylic acid and a metal

Answer 32

redox

Question 33

carboxylic acid + metal oxide

Answer 33

carboxylate salt + water both Hs from H2O from the acid

Question 34

carboxylic acid + alkalis

Answer 34

carboxylate salt + water one H from H2O from the acid, the other from the alkali

Question 35

carboxylic acid + carbonate

Answer 35

carboxylate salt + water + carbon dioxide

Question 36

how do you test for the carboxyl group

Answer 36

reaction with carbonate

Question 37

What is a derivative of a carboxylic acid

Answer 37

contain the acyl group O // R - C \

Question 38

what are four carboxylic acid derivatives

Answer 38

esters acyl chlorides acid anhydrides amide

Question 39

naming acyl chlorides e.g propanoic acid

Answer 39

-oyl chloride propyl chloride

Question 40

how is an acid anhydride formed

Answer 40

removal of water from two carboxylic acid molecules

Question 41

what is esterification

Answer 41

reaction of alcohol with a carboxylic acid to form an ester alcohol warmed with a carboxylic acid with a small amount of concentrated sulfuric acid (catalyst)

Question 42

alcohol + carboxylic acid

Answer 42

ester + water

Question 43

what is hydrolysis

Answer 43

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

Question 44

what is acid hydrolysis

Answer 44

ester heated under reflux with dilute aqueous acid ester broken down by water with acid acting as a catalyst reversible

Question 45

ester + water ->

Answer 45

carboxylic acid + alcohol

Question 46

alkaline hydrolysis

Answer 46

ester is heated under reflux with aqueous hydroxide ions irreversible

Question 47

ester + hydroxide ions ->

Answer 47

carboxylate ion + alcohol

Question 48

how do you prepare an acyl chloride?

Answer 48

carboxylic acid + thionyl chloride

Question 49

thionyl chloride

Answer 49

SOCl2

Question 50

carboxylic acid + thionyl chloride -> What are the safety precautions regarding this reaction?

Answer 50

acyl chloride + sulphur dioxide(g) + hydrochloric acid(g) SO2(g) an HCl(g) harmful gases reaction should be carried out in a fume cupboard

Question 51

why are acyl chlorides useful?

Answer 51

they are very reactive can be converted into carboxylic acids derivates with good yields

Question 52

acyl chloride + alcohol ->

Answer 52

ester + HCl

Question 53

acyl chloride + phenol ->

Answer 53

ester + HCl phenol ____ ___/ O \ HO \ ____/

Question 54

acyl chloride + water ->

Answer 54

carboxylic acids + HCl fumes

Question 55

acyl chloride + ammonia ->

Answer 55

primary amide + ammonium chloride COCl + 2NH3 -> CONH2 + NH4Cl

Question 56

acyl chloride + primary amine ->

Answer 56

secondary amide + HCl

Question 57

acid anhydrides

Answer 57

less reactive than acyl chlorides but react in the same way

Question 58

what type of intermolecular forces do molecules with the carbonyl group have

Answer 58

permanent dipole-dipole due to the polar C=O

Question 59

which bond in carbonyl compounds is usually responsible for its reactions and why

Answer 59

C=O the polarity of the bond (difference in electronegativity between C and O)

Question 60

what is fehling's solution and how is it used

Answer 60

copper complex ions blue test for an aldehyde, blue -> brick red reduction to Cu+2 ions

Question 61

why does a silver mirror form when an aldehyde is added to tollen's reagent

Answer 61

Ag+ ions are reduced to Ag(s)

Question 62

what is a reducing agent for aldehydes and ketone and what ions does it release in solution

Answer 62

NaBH4 H- ions

Question 63

how do you create a carboxylic acid from an aldehyde

Answer 63

oxidation acidified potassium dichromate (K2Cr2O7/H2SO4)