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Chemistry OCR A A-level yr 12 > Organic chemistry- Carbonyl and carboxylic acids > Flashcards

Organic chemistry- Carbonyl and carboxylic acids Flashcards

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1
Q

what is the functional group of aldehydes?

A

carbon atom of carbonyl group is attached to a hydrogen atom

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2
Q

what is methanal used for?

A

used in solution to preserve biological specimens

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3
Q

what is the functional group for a ketone?

A

carbonyl functional group is joined to two carbon atoms

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4
Q

what is propanone used for?

A

it is acetone, which is used as a solvent and used in nail varnish removers

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5
Q

what is octantal used for?

A

colourless fragrant liquid, responsible for the smell of oranges. It naturally occurs in citrus oils and is used in perfumes and flavour production in food industry

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6
Q

Why do ketones not undergo oxidation reactions?

A

lack of reactivity

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7
Q

What is the difference between the C=C double bond in alkenes and the C=O in carbonyl compounds?

A

-C=C in alkenes is non-polar
-C=O in carbonyl compounds is polar
-oxygen is more electronegative than carbon, greater share of electrons causing separation of charge.

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8
Q

why do aldehydes and ketones react with some nucleophiles?

A

due to polarity of C=O double bond. The reaction is called nucleophilic addition

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9
Q

what reducing agent is used to reduce aldehydes and ketones into alcohols?

A

Aldehyde or ketone is warmed with NaBH4 (sodium tetrahydridobrorate III) in aqueous solution

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10
Q

Aldehydes reduce to?

A

primary alcohols

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11
Q

Ketones reduce to?

A

secondary alcohols

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12
Q

Describe hydrogen cyanide?

A

HCN, it is colourless and poisonous. It cannot be used in an open laboratory as it boils slightly above room temp. Sodium cyanide and sulfuric acid are used to provide hydrogen cyanide.

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13
Q

Why is the reaction between carbonyl compounds (aldehydes and ketones) and hydrogen cyanide useful?

A

Increases length of carbon chain. A nitrile group (CN) and hydroxyl group is formed. These compounds are classed as hydroxynitriles

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14
Q

What is a carbonyl compound?

A

compound with C=O

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15
Q

In the nucleophilic addition reaction with NaBH4, what acts as the nucleophile?

A

hydride ion, H-

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16
Q

Describe the mechanism for the reaction between NaBH4 and carbonyl groups?

A

-hydride ion is attracted and donated to positive carbon atom
-dative covalent bond is formed between hydride ion and carbon atom of C=O double bond
-the pi C=O bond breaks by heterolytic fission forming a negative intermediate
-the oxygen atom of the intermediate donates a lone pair of electrons to a hydrogen atom in a water molecule. The intermediate becomes protonated to form an alcohol and lone hydroxyl group.

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17
Q

Describe the mechanism for the reaction with NaCN/H+?

A

-the cyanide ion, CN- is attracted to the C=O and a dative covalent bond form
-the pi bond breaks through heterolytic fission forming a negatively charged oxygen
-the immediate (oxygen) is protonated by a lone pair of electrons from a hydrogen ion.
-a hydroxynitrile is formed

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18
Q

How do you detect carbonyl compounds?

A

use Brady’s reagent . Positive result of yellow or orange precipitate

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19
Q

Describe Brady’s reagent?

A

normally dissolved in methanol and sulphuric acid as a pale orange solution. Solid Brady’s reagent is very hazardous due to friction or sudden blow causing explosion

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20
Q

How does Brady’s reagent work?

A

in condensation reaction as water is formed in nucleophilic addition. The NH2 group in Brady’s reagent adds across the C=O

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21
Q

how do you detect and aldehyde?

A

using tollen’s reagent, a solution of silver nitrate in aqueous ammonia. Positive result of a silver mirror

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22
Q

What are the reactions when using tollens reagent?

A

Ag+ acts as oxidising agent in presence of ammonia. Silver ions are reduced to silver and aldehyde is oxidised to carboxylic acid

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23
Q

what are the chemical equations when using tollens reagent?

A

-Ag+(aq) + e- —> Ag(s) (silver mirror)
-aldehyde + [O] —-> carboxylic acid

24
Q

what is the functional group for a carboxylic acid?

A

contain carbonyl group and hydroxyl group on the same carbon

25
Q

carboxylic acids are used for?

A

medicines e.g painkiller (aspirin)

26
Q

why are carboxylic acids soluble?

A

the C=O AND O-H bonds are polar, allowing hydrogen bonds to form with water molecules

27
Q

why does solubility decrease as number of carbon atoms increases?

A

carboxylic acids with up to four carbon atoms are soluble in water. The non-polar carbon chain has a greater effect on the overall polarity

28
Q

what kind of acid are carboxylic acids?

A

weak acids, they partially dissociate from H+ ions

29
Q

carboxylic acids take place in redox reactions with…

A

metals. They form hydrogen gas and carboxylate salt.

30
Q

carboxylic acids take place in neutralisation reactions with…

A

bases (alkalis, metal oxides, carbonates)

31
Q

carboxylic acids form what kind of salt?

A

carboxylate salts

32
Q

carboxylic acid + metal oxide forms?

A

carboxylate salt + water

33
Q

carboxylic acid + alkali forms?

A

carboxylate salt + water

34
Q

carboxylic acid + carbonate forms?

A

carboxylate salt + water +carbon dioxide

35
Q

how do you test for a carboxyl group?

A

react with carbonate. Carboxylic acids are the only common organic compound sufficiently acidic to react with carbonates

36
Q

what Is a devrivative of a carboxylic acid?

A

a compound that can be hydrolysed to form the parent carboxylic acid.

37
Q

what is an acyl group?

A

common sequence of atoms in the structure

38
Q

how do you name esters?

A

replace -ioc acid from -oate. The alkyl chain attached to the oxygen atom of the COO group is then added as the first word in the name

39
Q

how do you name acyl chlorides?

A

replace -oic acid with -oyl chloride

40
Q

how is an acid anhydride formed?

A

by removal of water from two carboxylic acid molecules

41
Q

what is esterification?

A

reaction of alcohol and carboxylic acid where is is warmed to form an ester an water. Use small amount of concentrated sulphuric acid which acts as a catalyst.

42
Q

what does esters smell like?

A

sweet smelling

43
Q

how can you easily detect the smell of an ester when making it from a carboxylic acid and alcohol?

A

add aqueous sodium carbonate which is a weak base to neutralise acid. This removes the smell of the carboxylic acid that hasn’t reacted making it easier to smell the ester.

44
Q

describe ethyl propanoate (common)?

A

colourless. Smells like pineapples. It is naturally produced in some fruits like kiwi and strawberries

45
Q

esters can be hydrolysed by what?

A

aqueous acid or alkali

46
Q

Explain the hydrolysis of ester using acid

A

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

47
Q

what are the products of the acid hydrolysis?

A

carboxylic acid and alcohol

48
Q

Explain the alkaline hydrolysis is also known as saponification

A

it is irreversible. The ester is heated under reflux with aqueous hydroxide ions.

49
Q

what are the products formed when an ester is hydrolysed using an alkaline?

A

carboxylate ion and an alcohol

50
Q

describe the oxidation of aldehydes?

A

can form carboxylic acids when refluxed with acidified dichromate ions usually potassium or sodium and dilute sulphuric acid.

51
Q

do ketones undergo oxidation reactions?

A

no

52
Q

what is the chemical test and observation of an alkene?

A

chemical test- bromine water
observation- colourless

53
Q

what is the chemical test and observation of an aldehyde?

A

test- tollens reagent and warm
observation- silver mirror

54
Q

what is the chemical test and observation of a carbonyl?

A

test- 2,4 DNP
observation- orange precipitate

55
Q

what is the chemical test and observation for a primary and secondary alcohol and aldehyde?

A

test- acidified potassium dichromate and warm in water bath
observation- orange precipitate

56
Q

what is the chemical test and observation from a carboxylic acid?

A

test- aqueous sodium carbonate
observation- effervescence

Chemistry OCR A A-level yr 12 (21 decks)

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