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ORGANIC CHEMISTRY (13) > Compounds containing Carbonyl group > Flashcards

Compounds containing Carbonyl group Flashcards

1
Q

Where is the carbonyl group present?

A

Found in aldehydes and ketones ONLY

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2
Q

What is the suffix when an aldehyde group is a substituent on a benzene ring?

A

-carbaldehyde

The carbon in the functional group is not included in the root name, eg benzene carbaldehyde

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3
Q

Physical properties of carbonyl compounds?

A
  • Carbonyl group is strongly polar due to the great difference in electronegativity between the carbon and oxygen
  • There are permanent dipole-dipole and van der Waals forces between molecules
  • BP of carbonyl compounds is higher than alkanes of comparable relative molecular mass (but alcohol has highest BP with H-bonds)
  • When carbonyl compound present in water, H-bonding may be expressed
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4
Q

Solubility in water?

A

Shorter chain aldehydes and ketones mix completely in water = H-bond forms between oxygen of carbonyl group of the compound and water
As length of carbon chain increases, carbonyl compounds are less soluble in water

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5
Q

States of ketones and aldehydes at room temperature?

A

Methanal is a gas at room temperature but other short-chain ketones or aldehydes are liquids with characteristic smells

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6
Q

Nucleophilic addition with cyanide ions

A

NaCN/KCN is used as source of CN-, followed by addition of dilute HCl for source of H+

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7
Q

Why can’t nucleophilic addition with CN- be carried out in a lab?

A

Due to the toxic nature of CN-

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8
Q

Why are hydroxynitriles useful in synthesis?

A

The -OH and -CN groups are reactive and can be transformed into other functional groups. The carbon chance has also been increased by one carbon from the starter reactants.

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9
Q

When is a racemic mixture formed during an nucleophilic addition reaction with CN-?

A

A racemate mixture is always formed with an aldehyde or when an UNSYMMETRICAL ketone is used = the CN- may attack from above or below the flat C=O group/trigonal planar structure

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10
Q

Why are ketones not easily oxidised to carboxylic acids unlike aldehydes?

A

They are lacking a C-H bond therefore for oxidation to take place further for a ketone, a C-C bond must break but a stronger oxidising agent must break this hydrocarbon chain of the ketone molecule; this results in a shorter chain molecule, carbon dioxide and water

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11
Q

What is the Fehling’s test made of?

A

It is a mixture of two solutions:

  • Fehling’s A contains Cu2+ ions (blue)
  • Fehling’s B contains alkali and complexing agent
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12
Q

What happens when an aldehyde is warmed with Fehling’s solution?

A

A brick red precipitate of copper (I) oxide is produced as the copper (II) oxidises the aldehyde to a carboxylic acid. The copper (II) is reduced to copper (I)

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13
Q

How to make Tollen’s reagent for the silver mirror test?

A

Tollen’s reagent contains a different complexing agent/complex ion which is [Ag(NH3)2]^+; this is formed when aqueous ammonia is added to a solution of AgNO3.

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14
Q

What is the redox that takes place in the silver mirror test?

A

The aldehyde is oxidised to a carboxylic acid whilst the Ag+ is reduced to Ag.
RCHO + [O] -> RCOOH
[Ag(NH3)2]^+ + e- -> Ag + 2NH3

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15
Q

What is a name for a reducing agent?

A 
Sodium tetrahybridoborate (III)/Sodium borohydride = NaBH4 (aq)
This generates H- (hydride ions) = this acts as a nucleophile
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16
Q

Reduction of aldehydes/ketones to primary/secondary alcohols consists of what reaction mechanism?

A

Nucleophilic addition reactions. H- is from the reducing agent and H+ is from the solvent.

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17
Q

What two functional groups comprise a carboxylic acid?

A
  • A carbonyl group

- A hydroxy group

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18
Q

What effect does having two functional groups present on a carboxylic acid pose?

A

The properties of each group is changed. The -OH group is more acidic in carboxylic acid than it is in alcohols.

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19
Q

When a carboxylic acid is attached to the benzene ring, what is the suffix?

A

-carboxylic acid

The carbon of the functional group is not counted as part of the main chain/root, for example: benzenecarboxylic acid

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20
Q

What are the physical properties of carboxylic acids?

A
  • They can form H-bonds with water molecules and carboxylic acids (up to and including 4 carbons) are completely soluble in water
  • They have higher MP than alkanes of similar relative molecular mass
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21
Q

Can carboxylic acids form H-bonds with one another?

A

Yes but in the solid state. When two carboxylic acid molecules H-bond together, the pair formed is called a dimer

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22
Q

How to identify carboxylic acids?

A

We could measure the MP and compare it to known MP values using a thiele tube or it can be found electrically

23
Q

Why is pure ethanoic acid called glacial ethanoic acid?

A

Because on a cold day, the pure ethanoic acid may freeze

24
Q

Uses of esters?

A

Short chain esters are fairly volatile with pleasant fruity smells and are often used in flavouring, perfumes, solvents and plasticisers
- Fats and oils are esters with longer carbon chains

25
Q

What makes a carboxylate ion MORE stable?

A

The delocalisation as the negative charge is shared over the whole of the carboxylate group. The stability is what allows the H+ to release and cause the molecules to be acidic (if releasing protons - it acts as acid)

26
Q

IF A CARBOXYLIC ACID REACTS WITH _____CARBONATE..

A

CO2 is likely to be formed

27
Q

What distinguishes a carboxylic acid from another compound with the -OH group such as alcohols?

A

Carboxylic acids are weak acids but are strong enough to react with sodium hydrogencarbonate to release CO2

28
Q

Ethanoic acid + sodium hydrogencarbonate -> ?

A

Ethanoic acid + sodium hydrogencarbonate -> sodium ethanoate + water + carbon dioxide

CH3COOH (aq) + NAHCO3 (aq) -> CH3COONa (aq) + H20 (l) + CO2 (g)

29
Q

Ethanoic acid + sodium hydrogencarbonate -> ?

A

Ethanoic acid + sodium hydrogencarbonate -> sodium ethanoate + water + carbon dioxide

CH3COOH (aq) + NaHCO3 (aq) -> CH3COONa (aq) + H20 (l) + CO2 (g)

Other possibilities instead of NaHCO3 (aq) is Na2CO3 (s) or solid NaHCO3.. All still release CO2 with a carboxylic acid

30
Q

Reactions of acids?

NOTE: Carboxylic acids are proton donors and show the typical reactions of acids

A

Carboxylic acids form ionic salts with more reactive metals, alkalis, metal oxides and metal carbonates.

Ethanoic acid + sodium hydroxide -> sodium ethanoate + water
CH3COOH (aq) + NaOH (aq) -> CH3COOONa (aq) + H20 (l)

Ethanoic acid + sodium carbonate -> sodim ethanoate + water + carbon dioxide
2CH3COOH (aq) + NaCO3 (aq) -> 2CH3COONa (aq) + H20 (l) + CO2 (g)

31
Q

Formation of esters?

A

Carboxylic acids react with alcohols to form esters
> speeded up by a strong acid catalyst
> reversible reaction which forms an equilibrium mixture of reactants and products
Ethanoic acid + ethanol ~ ethyl ethanoate + water

32
Q

Hydrolysis of esters?

A

The carbonyl atom has a delta positive charge which is attacked by H20 acting as a nucleophile.
Ester + water ~ carboxylic acid + alcohol
Again a H+ catalyst is present
The hydrolysis (Reaction with water) does not go to completion and produces an equilibrium mixture containing ester, water, acid and alcohol

33
Q

Does the acid catalyst affect the composition of the equilibrium mixture or the position of equilibrium?

A

No, it only affects the rate at which equilibrium is reached

34
Q

How does base catalyse hydrolysis of esters work?

A

The salt of the acid is produced rather than the carboxylic acid itself which means that the acid is removed from the reaction mixture… THEREFORE AN EQUILIBRIUM MIXTURE IS NOT ESTABLISHED AND REACTION GOES TO COMPLETION, THERE WILL BE MORE PRODUCT IN THE MIXTURE.

35
Q

What can be a source of H+ catalyst in esterification?

A

Concentrated H2SO4

36
Q

How can ester be removed from reaction mixture?

A

Ester will be more volatile than original reactants and can be distilled off the reaction mixture

37
Q

What is the difference between a fat and an oil?

A

Oils are liquids at room temperature while fats are solids

38
Q

What do oils and fats comprise of?

A

They contain 3 molecules of long chain carboxylic acids (fatty acids) and an alcohol (glycerol)

Fats and oils are referred to as triglycerides as they are based on glycerol

39
Q

Fats and oils can be hydrolysed in acid conditions to give a mixture of glycerol and the component fatty acids… What are the products and what is it boiled with?

A

They can be hydrolysed by boiling with NaOH. The products are glycerol and a mixture of sodium salts based on the three acids which formed part of the ester.

40
Q

What is special about these salts from the hydrolysis of fats and oils?

A

These salts are soaps. A soap can be a mixture containing many different salts. The type of salt depends on the fatty acid initially present in the ester.
These salts are ionic and can dissociate to form Na+ and RCOO- in the case of sodium salts.
RCOO- has two distinct ends: a long hydrocarbon chain (R) which is non-polar and the COO- group which is polar and ionic.

The hydrocarbon can mix with grease while the COO- can mix with water. Therefore the molecules allow grease and water to mix and therefore these salts can be used as cleaning agents.

41
Q

Information about properties of propane-1,2,3-triol (glycerol)?

A
  • Glycerol has 3 OH bonds so it can form H-bond and is very soluble in water.
  • Used highly in pharmaceutical and cosmetic preparations because it attracts water and prevents ointments and creams drying out.
  • Used a solvent in many medicines and present in toothpaste
  • Used as solvent in food industry, for eg, food colouring
  • Used to plasticise various materials like sheets and gaskets, cellophane and special quality papers
42
Q

Can plasticisers leak away?

A

Yes they can over time which leaves plastic brittle and inflexible. PVC may contain up to 50% plasticisers (esters)

43
Q

Importance and making of biodiesel?

A

Biodiesel is made from oils derived from crops such as rapeseed. Rapeseed is a triglyceride.
To make biodiesel, the oil is reacted with methanol (with strong alkali as a catalyst: KOH) to form a mixture of methyl esters. Methyl esters can be used as a fuel in diesel vehicles with little or NO modification.

Chemistry/process is simple so some make biodiesel at home using used chip-shop oil.

44
Q

What is acylation?

ACYLATION = NUCLEOPHILIC ADDITION-ELIMINATION REACTION.

A

Acylation is the process of which the acyl group is introduced into another molecule.

45
Q

What are the three acid derivatives?

There is a group of compounds called acid derivatives which all have the acyl group as part of their structure.

A
  • Acid chlorides
  • Acid anhydrides
  • Esters

Acid derivatives are derived from carboxylic acids

46
Q

NOTE: In acylation, the nucleophile is the one which has acquired the acyl group.

A

The nucleophile replaces the Z in the general formula leaving it attached to an acyl group.

47
Q

What three factors determines how readily the reaction of acylation occurs?

A
  1. The magnitude of the partially positive charge on the carbonyl carbon which in turn depends on the electron-releasing or attracting power of Z
  2. How easily Z is lost (Z is called the leaving group)
  3. How good the nucleophile is

Factors 1 and 2 tend to be linked - groups which strongly attract electrons tend to form stable negative ions, Z- and are good leaving groups.

48
Q

What are the nucleophiles that acid anhydrides and acid chlorides react with in terms of reactivity (highest to lowest reactivity scale)?

A

Most reactive: Primary amine
Ammonia
Alcohol
Least reactive: water

49
Q

What are the products of reactions of nucleophiles with acyl chlorides and anhydrides? (Room temperature conditions)

A 
NUCLEOPHILE / PRODUCT
Ammonia / amide
Amine / N-substituted amide
Alcohol / ester
Water / carboxylic acid
50
Q

Why do nucleophiles lose a H+ during a nucleophilic addition-elimination reaction?

A

Because nucleophiles are neutral

51
Q

NOTE: When ammonia is the nucleophile, the H+ lost then reacts with a second ammonia molecule to form NH4+

A

CH3COCl + 2NH3 -> CH3CONH2 + NH4Cl

Ethanoyl chloride + ammonia -> Ethanamide + Ammonium chloride

52
Q

What is ethanoic anhydride more commonly used than ethanoyl chloride as an acylating agent?

A
  • it is cheaper
  • Less corrosive
  • Does not readily react with H20
  • It is safer as by-product of its reaction is ethanoic acid rather than HCl
53
Q

ASPIRIN PURPOSE AND RISKS?

A
  • Aspirin reduces the risk of heart attacks and some cancers.
  • It also reduces fevers
  • It however can cause intestinal bleeding
54
Q

What is the aspirin reaction?

A

Salicylic acid + ethanoyl anhydride -> aspirin + ethanoic acid

ORGANIC CHEMISTRY (13) (2 decks)

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