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Chemistry Module 6 > 6.1.2 Carbonyl Compounds > Flashcards

6.1.2 Carbonyl Compounds Flashcards

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1
Q

carbonyls definition

A

compounds with a C=O

aldehydes or ketones

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2
Q

how to tell if a compound is an aldehyde

A

if C=O is on the end of the chain with a H attached

name ends in -al

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3
Q

how to tell if a compound is a ketone

A

if the C=O is in the middle of the chain

name ends in -one

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4
Q

carbonyls solubility in water

A

smaller are soluble in water

because they can form hydrogen bonds with water

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5
Q

how do pure carbonyls bond

A

can’t hydrogen bond

bond instead by permanent dipole- dipole forces

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6
Q

how do carbonyls react

A

C=O is polarised because O is more electronegative than carbon
positive carbon attracts nucleophiles

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7
Q

compare bond strength of C=C and C=O

A

C=O is stronger than C=C in alkenes so doesn’t undergo addition reactions easily

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8
Q

oxidation of aldehydes

A

aldehydes -> carboxylic acids
potassium dichromate (VI) solution and dilute sulfuric acid
heat under reflux
orange dichromate reduces to the green Cr3+ ion

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9
Q

how else can aldehydes be oxidised

A

using Tollen’s reagent

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10
Q

test for aldehydes

A

Tollen’s reagent

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11
Q

Tollen’s reagent

reagent
condition
reaction
observation

A

reagent: Tollen’s reagent formed by mixing aqueous ammonia and silver nitrate, active substance complex ion of [Ag(NH3)2]+
conditions: heat gently
reaction: aldehydes only oxidised by tollens into a carboxylic acid, silver (I) ions reduced to silver atoms
observation: with aldehydes silver mirror forms coating the test tube, ketones don’t change

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12
Q

Tollens reagent ionic equation

with ethanal

A

CH3CHO + 2Ag+ + H2O -> CH3COOH + 2Ag + 2H+

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13
Q

Reduction of carbonyls

reagents
conditions
mechanism

A 
Reagents: NaBH4 in aqueous ethanol 
Conditions: room temperature and pressure
NUCLEOPHILIC ADDITION
Aldehydes reduced to primary alcohols
Ketones reduced to secondary alcohols
Need 2 reducing agents
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14
Q

What are aldehydes reduced to

A

Primary alcohols

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15
Q

What are ketones reduced to

A

Secondary alcohols

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16
Q

Reducing agent notation

A

[H]

When adding make an oxygen sandwich

17
Q

Examples of reducing agents to reduce carbonyls to alcohols

A

NaBH4= sodium tetrahydridoborate

LiAlH4 =lithium tetrahydridoaluminate

18
Q

Describe the nucleophilic addition mechanism for carbonyl reduction

A 
Delta plus delta minus on C=O 
H- attacks delta plus on carbon 
Arrow from middle of C=O to the O
Lone pair on O draw arrow to H on water molecule
Middle of O-H bond draw line to O
Forms OH on the carbonyl and OH-
19
Q

What does NaBH4 contain

A

Source of nucleophilic hydride ions (H-)

Attracted to positivr carbon in C=O

20
Q

Hydride ion

A

H-

21
Q

Catalytic hydrogenation

A 
Also be reduced using catalytic hydrogenation 
Reagent: hydrogen and nickel catalyst
Conditions: high pressure
Examples: 
CH3CHO + H2 -> CH3CH2OH 
CH3COCH3 + H2 -> CH3CH(OH)CH3
22
Q

What is hydroxynitrile

A 
R
          |
NC— C —OH
          |
          H
23
Q

Addition of hydrogen cyanide to carbonyls to form hydroxynitrile

reaction
reagent
conditions
mechanism

A

Reaction: carbonyl -> hydroxynitrile
Reagent: sodium cyanide (NaCN) and dilute sulfuric acid
Conditions: room temperature and pressure
Mechanism: nucleophilic addition

24
Q

What do NaCN and H2SO4 provide in hydrogen cyanide to carbonyls mechanism

A

CN- ions
H+ ions
For second step of mechanism

25
Q

Naming hydroxy nitriles

A

CN becomes part of the main chain

26
Q

Nucleophilic addition mechanism hydrogen cyanide to carbonyls

A

C=O delta plus on C and delta minus on O
Line from double bond to O
CN- (lone pair also) attacks C+
Lone pair on oxygen donated to H+ from sulfuric acid

27
Q

Test for carbonyl group

A

Using 2,4-DNP
Produces orange precipitate
Then if positive use tollens to test if aldehyde or ketone

28
Q

How can you also identify which carbonyl was used

A

Add 2,4-DNP then orange ppt will form, derivative of carbonyl group then…

  1. Filter crystals using Buchner funnel and water pump
  2. Orange ppt is impure so dissolve crystals in smallest amount of hot solvent (ethanol)
  3. Put test tube in ice water to allow pure solid to recrystallise
  4. Filter again using Buchner funnel and water pump, have a pure solid
  5. Find melting point of pure solid using machine
  6. Compare to known database of melting points for carbonyl derivatives to identify carbonyls
29
Q

What is 2,4-DNP

A

2,4-dinitro phenylhydrazine

30
Q

2,4-DNP way to remember process

A 
filter
dissolve 
recrystalise 
filter
dry
melt
check database

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