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A Level Chemistry > Carbonyl And Carboxylic Acids > Flashcards

Carbonyl And Carboxylic Acids Flashcards

1
Q

What is the structure of bonds in carbonyl group
+ draw it

A
  • carbonyl group consisted of C=O
    This bond is polar due to different electronegativity of elements
    Dipoles therefore on the Carbon (+) and Oxygen (-)
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2
Q

Draw the formation of double bond in carbonyl group

A

See notes
2 p orbitals on Carbon and oxygen which overlap to form a pi bond abounded and below plane. As oxygen is more electronegative that carbon the oxygen side of the overlap is larger

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3
Q

Draw the formation of double bond in carbonyl group

A

See notes
2 p orbitals on Carbon and oxygen which overlap to form a pi bond abounded and below plane. As oxygen is more electronegative that carbon the oxygen side of the overlap is larger

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4
Q

Describe production of aldehyde

A

Oxidation of primary alcohol
- distil off the aldehyde with acidified potassium dichromate (Cr2O7 2-/ H+)
- Cr2O7 2-/H+ turns from orange to green as it gets reduced
- distillate collected = aldehyde

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5
Q

Oxidation properties of carbonyl compounds

A

Aldehydes
- easily oxidised into acids

Ketones
- only oxidised under vigorous conditions

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6
Q

Ways to identify carbonyl group/ compounds

A

1) peak at 1400-1600 cm-1 on IR spec

2) orange precipitate formed with 2,4- dinitrophenylhydrazine

3) tollen’s test
Aldehyde = silver mirror produced Ketone = remains colourless

4) Fehling’s solution
Aldehyde = red precipitate formed. Ketone = no reaction

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7
Q

How is addition reactions different in carbonyl and alkenes
And why

A

Carbonyl
- C=O bond is polar
Attacked by nucleophiles
So nucleophilic addition

Alkene
- C=C bond is non polar
Attacked by electrophile
So electrophilic addition

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8
Q

Reaction for nucleophilic addition (reduction) of aldehyde and ketones
Reagent
Conditions
Mechanism
Products
Equation

A

Reagent - sodium borohydride NaBH4
Conditions - aqueous or alcoholic solution
Mechanism - nucleophilic addition
Products - aldehyde —> primary alcohol
Ketones —> secondary alcohol
Equation- CH3CHO + 2[H] —> CH3CH2OH
CH3COCH3 + 2[H] —> CH3CHOHCH3

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9
Q

Mechanism of nucleophilic addition (reduction) of aldehyde

A

See notes
Remember to put the dipoles on the carbon and oxygen
1) H- acts as nucleophile and attacks the C(+)
An electron pair from the C=C moves onto O asking it -ive
A lone pair on oxygen removes a proton from water
Overall, there is addition of hydrogen

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10
Q

Reaction of HCN and aldehyde
- reagents
-conditions
- products
- equation
-mechanism

A

Reagent = potassium cyanide with dilute acid
Conditions - reflux
Products - hydroxynitrile
Equation- CH3CHO + HCN —> CH3CH(OH)CN
Mechanism- nucleophilic addition
see notes

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11
Q

Draw the mechanism for reaction between HCN and aldehyde
Nucleophilic addition

A

1) draw the dipoles on carbon and oxygen
2) CN- acts as a nucleophile and attacks the slightly positive C
One of the C=O bond breaks; a pair of electrons goes onto the O
3) A pair of electrons is used to form a bond with H+
4) Overall, there is the addition of HCN

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12
Q

Compare the boiling points of carboxylic acids, aldehydes, ketones and alcohols

A

Carboxylic acid and alcohols have higher b.p that aldehydes and ketones
as aldehydes and ketones have no H group so don’t form H bonds which are strong and require more enters to break than London forces alone.

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13
Q

Explain the tollen’s test (silver mirror test)
+ results

A

Tollen’s reagent = ammoniacal silver nitrate solution
Acts as a mild oxidising agent and will oxidise aldehydes but not ketones
Silver(I) ion is reduced to silver

+ if positive (aldehyde) silver precipitate forms
Ketones remain colourless > negative result

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14
Q

How can you identify a carbonyl group with 2,4-dinitrophenylhydrazine? + how can you use this to identify aldehyde and ketone if tollen’s test not possible

A

If Brandy’s reagent added (yellow solution) & carbonyl group present
a yellow/orange precipitate will form

This orange precipitate can be recrystallised to from pure crystals
Then used to measure melting point
Then compare melting point to a database to determine aldehyde/ketone

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15
Q

How can you use Fehling’s solution to identify aldehyde/ketone

A
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16
Q

Method of hydrogenation (reduction) with hydrogen + aldehyde/ketone + conditions
+ equations

A

A nickel or platinum catalyst needed

Aldehyde
CH3CHO + H2 —> CH3CH2OH

Ketone
CH3COCH3 + H2 —> CH3CHOHCH3

17
Q

Describe solubility of carboxylic acids

A
  • very soluble in organic solvents
  • soluble in water due to H bonds
  • small ones dissolve readily in cold water
  • as mass increases the solubility decreases
18
Q

Describe boiling points of carboxylic acids

A

Increases as size increases - increased London forces
Carboxylic acids have high boiling points for their relative masses
Arise from inter- molecular hydrogen bonding due to polar O-H bonds
Additional inter-molecular attraction = more energy to separate molecules

19
Q

How can carboxylic acid be prepared (5 ways)

A

Oxidation of aldehydes
Hydrolysis of esters
Hydrolysis of acyl chlorides
Hydrolysis of nitriles
Hydrolysis of amides

20
Q

Reaction of carboxylic acid and carbonates

A

Produce salt and carbon dioxide
2 RCOOH + Na2CO3 —> 2ROO-Na+ +CO2 +H2O

21
Q

Reaction of carboxylic acids and metals

A

Produced a salt and hydrogen
2RCOOH + Mg —> (RCOO-)2Mg2+ + H2

22
Q

Reaction of carboxylic acids and metal oxides

A

Produces a salt and water
2RCOOH + MgO —> (RCOO-)2Mg2+ + H2O

23
Q

Name some derivatives for carboxylic acids
identify the acyl group for each

A

Ester
Acyl chloride
Acid anhydride
Amide

Acyl group = R-C=O group

24
Q

Esterification reaction
1) reagents needed
2) conditions
3) equation

A

Reagents
- alcohol (e.g methanol) & carboxylic acid (e.g ethanoic acid)
Conditions
- reflux
Equation
CH3OH + CH3COOH —> CH3COOCH3 + H20

25
Q

How to identify ester
- using name

+ identifying alkyl group

A

Ester will end in -oate
E.g methyl ethanoate

Alkyl group R-COO-R

26
Q

Name ester made from propanol and ethanoic acid

A

Propanol + ethanoic acid —> propyl ethanoate
The alcohol name is the start then the carboxylic acid get the **-oic acid88 suffix replaced with -oate

27
Q

Compare the synthesis of ester
From carboxylic acid and acyl chlorides

A

Carboxylic acids - slow, equilibrium process
Acyl chlorides - faster, but more care must be taken

28
Q

How do you name an acyl chloride from carboxylic acid

A

To name acyl chloride
1. Remove the -Oic acid suffix from carboxylic acid
2. Replace with -oyl chloride

E.g propanoic acid —> propanoyl chloride

29
Q

Chlorination reaction with carboxylic acid
1) reagents
2) conditions
3) product
4) Equation

A

reagents
- thionyl chloride (SOCl2)
conditions
- dry conditions
product
- acyl chloride
equation
- CH3COOH + SOCl2 —> CH3COCl + SO2 + HCl

30
Q

Physical properties of esters

A

Colourless liquid
Insoluble in water
Unreactive

31
Q

How to name acyl chloride

A

Name from the corresponding acid
- remove ic and add yl chloride

E.g ethanoic acid —> ethanoyl chloride

32
Q

Methods to prepare acyl chloride from carboxylic acids

A

Method 1
Reagent - thionyl chloride SOCl2
Conditions - dry conditions
Equation - CH3COOH + SOCl2 —> CH3COCl + SO2 + HCl

Method 2
Regent- phosphorus(V) chloride PCl5
Conditions- dry conditions
Equation - CH3COOH + PCl5 —> CH3COCl + POCl3 + HCl

33
Q

Chemical properties of acyl chlorides

A
  • colourless liquid which fumes in moist air
  • gets attacked at the + carbon centre by neucleophiles
  • nucleophiles include water, alcohols, ammonia and amines
  • undergo addition-elimination reactions
  • much MORE REACTIVE than Carboxylic acid and acid anhydrides
34
Q

Reaction of water and acyl chlorides
1) products
2) condtions
3) equation
4) mechanism

A

products
- carboxylic acids and HCl
conditions
- cold water
equations
- CH3COCl(l) + H2O(l) —> CH3COOH(aq) +HCl(aq)
mechanism
- addition elimination
lone pair of electrons on H2O attach the carbon causing electrons to move to double bonded O this causes 3 lone pairs around the O and H2O is attached. Electrons in this intermediate also move to Cl group removing it to from nucleophile. Positive H on H20 group is also releasaed to from COOH group
(See notes)

35
Q

Reactions of Alcohols and acyl chlorides
1) products
2) conditions
3) equation
4)mechanism

A

products
- ester + HCl
conditions
- reflux in dry conditions
equation
- CH3COCl(l) + CH3OH(l) —> CH3COOCH3(l) + HCl(g)
mechanism
- addition elimination
lone pair of electrons on oxygen of H-O-CH3 attach the carbon causing electrons to move to double bonded O this causes 3 lone pairs around the O and OH(CH3) is attached. Electrons in this intermediate also move to Cl group removing it to from nucleophile. Positive H on OH(CH3) group is also releasaed to from COOH group

36
Q

Reaction of amines and acyl chlorides
1) products
2) conditions
3) equation
4) mechanism

A

products
- N-Substituted amine + HCl
conditions
- anhydrous
equation
- CH3COCl(l) + C2H5NH2(aq) —> CH3CONHC2H5(s) + HCl(g)
CH3COCl(l) + 2C2H5NH2(aq) —> CH3CONHC2H5(l) + C2H5NH3Cl(s)
mechanism
- addition elimination
lone pair of electrons on N of NH2R attach the carbon causing electrons to move to double bonded O this causes 3 lone pairs around the O and NH2R is attached. Electrons in this intermediate also move to Cl group removing it to from nucleophile. Positive H on NH2R group is also releasaed to from C-NHR group

37
Q

Reaction of ammonia and acyl chlorides
1) products
2) conditions
3) equation
4) mechanism

A

products
- amide + HCl
conditions
- low temperature and excess ammonia
equation
- CH3COCl(l) + NH3(aq) —> CH3CONH2(s) + HCl(g)
CH3COCl(l) + 2NH3(aq) —> CH3CONH2(s) + NH4Cl(s)
**mechanism*
- addition elimination
lone pair of electrons on N of NH3 attach the carbon causing electrons to move to double bonded O this causes 3 lone pairs around the O and NH3 is attached. Electrons in this intermediate also move to Cl group removing it to from nucleophile. Positive H on NH3 group is also releasaed to from C(O)-NH2 group

38
Q

Identification of amines

A

Function group - NH2
Naming - amine ending
can be primary, secondary, tertiary and ammonium salts = quaternary

A Level Chemistry (12 decks)

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