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CH0003 > Carbonyl Compounds > Flashcards

Carbonyl Compounds Flashcards

1
Q

What is the carbonyl group

A

C=O

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2
Q

Why is carbonyl polarised

A

Oxygen is more electronegative than carbon so electrons are more attracted towards the oxygen end of the bond

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3
Q

Why part of the carbonyl reacts with nucleophiles

A

The carbon

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4
Q

Which part of the carbonyl reacts with electrophiles

A

The oxygen

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5
Q

Describe aldehydes

A

Carbonyl group with one hydrogen and one alkyl or aryl (R-CO-H). Names end in -al or -aldehyde.

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6
Q

What are ketones

A

Carbonyl group with two alkyl or aryl substituents (R-CO-R). Names end in -one

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7
Q

Why are aldehydes usually more reactive than ketones

A

Inductive effect and steric hindrance

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8
Q

Why does inductive effect make aldehydes more reactive than ketones

A

The alkyl groups are electron donating (relative to the H), reduce the +ve charge on the carbonyl carbon and make it less attractive to nucleophiles

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9
Q

Why does steric hindrance make aldehydes more reactive than ketones

A

Alkyl groups get in the way of the approaching reagent. Aldehydes have a small hydrogen atom which does not get in the way of the nucleophile, whereas ketones have two substituents which repel the nucleophile

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10
Q

What happens with addition of water (hydration) of carbonyls

A

A reversible reaction. Double bond of oxygen to carbon breaks and two OH groups form and bond to carbon. However equilibrium usually favours the starting material

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11
Q

Describe nucleophilic addition of alcohols

A

Alcohols added to carbonyls is a reversible reaction. The first product is a hemiacetal (formed under an acid or base catalyst). Under an acid catalyst only the hemiacetal reacts to give an acetal.

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12
Q

Describe the nucleophilic addition of alcohols to carbonyls to form hemiacetals and acetals

A

Ketone + OH group from alcohol (with acid or base catalyst) -> hemiacetal (OH group and O with an open bond) (with an acid catalyst) -> acetal (no more OH group, two O groups with open bonds) and water

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13
Q

What is the significance of the formation of an acetal from the nucleophilic addition of alcohols to carbonyls being reversible

A

To make an acetal you add excess alcohol and remove water (distill it off). To hydrolyse an acetal you add dilute acid (large excess of water). Le Chatelier’s principle

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14
Q

What is addition of hydrogen (reduction) to carbonyls used for

A

To make alcohols from aldehydes or ketones.

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15
Q

How is the addition of hydrogen to carbonyls carried out

A

Done by adding H- (hydride) from reagent like LiAIH4 which gives electrons to oxygen of carbonyl making it -ve. Then adding H+ (from acid) to the reaction flask after which forms OH and so alcohol

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16
Q

What happens during oxidation of carbonyls

A

Requires an oxidising agent which becomes reduced during the reaction. Aldehyde oxidised to form OH on the H group (carboxylic acid)

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17
Q

What can be used to test for aldehydes

A

Fehling’s reagent (CU2+ in aqueous sodium tartrate) and Benedict’s reagent (Cu2+ in aqueous sodium citrate) give a reddy born precipitate of Cu2) when in the presence of an aldehyde

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18
Q

What does Tollen’s reagent give when in the presence of an aldehyde

A

A silver mirror (as is Ag+ in aqueous ammonia)

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19
Q

What does nucleophilic addition of primary amines with aldehydes or ketones produce

A

An imine

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20
Q

What happens when you add an amine to an aldehyde or ketone

A

Produces an imine and water. Imine has a C=N bond and the N is bonded to an R group.

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21
Q

What does the fact that the nucleophilic addition of primary amines and carbonyls is reversible mean

A

Imines are easily hydrolysed. Have to distil off water to shift equilibrium

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22
Q

What reactions do hydrazines undergo

A

Nucleophilic addition to form hydrozones and water. Hydrozones are reasonably stable towards hydrolysis

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23
Q

When is glucose a hemiacetal

A

When it is in its cyclic form

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24
Q

How does glucose form a hemiacetal

A

Undergoes intramolecular hemiacetal formation to form a ring. Glucose exists predominantly in its cyclic form

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25
Q

What functional groups does glucose have

A

Both an aldehyde and alcohol functional groups

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26
Q

What is an example of an aldehyde in equilibrium with a hemiacetal

A

Glucose

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27
Q

What is an example of a ketone in equilibrium with a hemiacetal

A

Fructose

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28
Q

What is fructose in its open chain form

A

A ketone

29
Q

What is fructose in its cyclic form

A

A hemiacetal

30
Q

What is sucrose

A

A disaccharide consisting of glucose and fructose. Two hemiacetals

31
Q

What is the functional groups of carboxylic acids and how do you name them

A

-COOH (CO2H) functional group. Names end in -oic acid

32
Q

What is the formula of propanoic acid

A

CH3CH2CO2H

33
Q

What are the bonding and physical properties of carboxylic acids

A

Have higher boiling points than corresponding alkanes and alcohols. High boiling points due to strong hydrogen bonds between acid molecules

34
Q

What do carboxylic acid molecules form in liquid and gas

A

Hydrogen bonded dimers. H of OH on one molecule forms hydrogen bond with O on other molecule and vice-versa

35
Q

How are carboxylic acids synthesised

A

Alcohol oxidised to aldehyde which is oxidised to carboxylic acid. Use H2SO4 or KMnO4 as reagents

36
Q

Describe the acidity of carboxylic acids

A

The OH proton can be lost to bases. So in water can lose H to form caboxylate ion (-ve) and H3O+

37
Q

Describe the structure of a carboxylate ion

A

Charge is shared between both oxygen atoms (resonance). Both C-O bonds are the same length. Bond length is between that of a single and double bond

38
Q

Describe acid strengths

A

In terms of electron withdrawing groups they stabilise the negatively charged carboxylate and increase in acid strength. Large Ka indicated a stronger acid

39
Q

Give examples of where carboxylic acids are important intermediated in metabolism of carbohydrates

A

Glycolysis, citric acid cycle

40
Q

Order anydride, ester and acid chloride in terms of most to least reactive

A

Acid chloride > anhydride > ester

41
Q

Describe reactions of acid derivates

A

RCOY (+ nucleophile) -> RC)Nu + Y-. Y is the leaving group which departs during the reaction taking a pair of electrons with it

42
Q

What are acid halides useful for

A

Making acid derivatives. They are prepared from acids. RCOOH + COCl2 -> RCOCl. Could also used PCl3

43
Q

How do you convert acid halides into acid derivatives

A

By reacting them with nucleophiles.

44
Q

How do you make a carboxylic acid from acid chloride

A

Add H2O

45
Q

How do you make an ester from acid chloride

A

Add R’OH

46
Q

How do you make a primary amide from acid chlride

A

Add NH3

47
Q

How do you make a secondary amide from acid chloride

A

Add R’NH2

48
Q

What de acid halides lose when reacting with nucleophiles to be converted into other acid derivatives

A

The halide (e.g. Cl)

49
Q

What are the carboxylic acid derivateves

A

Acid halide (X= F, Cl, Br, I), ester, acid anhydride, amide

50
Q

What are the molecules that can be formed when a carbonyl group is bonded to an electronegative element

A

Propanoyl chloride, ethyl acetate, ethanoic anhydride, N-methyl-propioamide

51
Q

What test can you use to distinguish and amine from an amide

A

Amines react with ninhydrin to give a blue colour, amides do not.

52
Q

What is an amide

A

C=O and NH2

53
Q

What is an amine

A

Just NH2

54
Q

How can amides can have 2 forms

A

The C and N can form a partial double bond giving the O a negative charge

55
Q

Which 2 ways can esters be synthesised

A

From acid chlorides (add R’OH) or using an alcohol, carboxylic acid and strong acid catalyst (HCl or conc. H2SO4)

56
Q

How do you make esters from alcohols, carboxylic acid and strong acid catalyst

A

Add excess alcohol to push the equilibrium towards the products

57
Q

How do you hydrolyse an ester to a carboxylic acid and alcohol

A

Use dilute aqueous acid

58
Q

Describe basic ester hydrolysis (saponification)

A

Ester (+NaOH and water) -> carboxylate salt and alcohol

59
Q

Why is basic ester hydrolysis not reversible

A

Once formed the carboxylic acid is deprotonated by the base to form a salt. The negatively charged carboxylate is not attacked by the alcohol nucleophile. The reaction is irreversible.

60
Q

How much base do you need to add to basic ester hydrolysis

A

One equivalent of base is used up, therefore need to add at least one equivalent

61
Q

What is saponification (basic ester hydrolysis) used for

A

To make soaps from fats

62
Q

How do you remove the carboxylic acid after saponification

A

By adding a stronger acid (e.g. HCl) to protonate it. Convert carboxylic salt to carboxylic acid

63
Q

How do you produce biodiesel and what catalyst is used

A

By reacting methanol with a fat. Reaction is catalysed by NaOCH3. Biodiesel is fatty acid methyl ester

64
Q

What are uses amides

A

Polymers- wool and silk are natural polyamides (proteins)

65
Q

How can you test for proteins/peptides

A

Use Biuret test. GIves a purple/ violet colour with proteins/ peptides, stays blue otherwise

66
Q

What is nylon

A

An artificial polyamide

67
Q

How are polyesters made

A

Reaction of a diester (or acid) with a diol.

68
Q

What is an example of a polyester

A

PET (polyethylene terephalate)

CH0003 (12 decks)

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