Carbonyls (aldehydes and ketones)

Question 1

Aldehyde naming

Answer 1

C=O on first carbon, no number required.

Question 2

Ketone naming

Answer 2

Counting longest carbon chaining, smallest number possible for carbonyl carbon.

Question 3

What does Fehling’s and Tollens’ test for

Answer 3

Aldehyde

Question 4

What does 2,4-DNPH test for

Answer 4

Carbonyl

Question 5

What does iodoform test for

Answer 5

Methyl ketone (including ethanal), secondary methyl alcohol (including ethanol)

Question 6

Intermolecular forces of aldehydes and ketones

Answer 6

They have London forces, permanent dipole forces. Can form H bonds but not with itself due to no H bonded to NOF therefore soluble in water.

Question 7

How does Fehling’s test work

Answer 7

Blue solution containing CuO when warmed with aldehyde will oxidise the aldehyde and reduce the Cu2+ to Cu+ which appears as a brick red precipitate.

Question 8

How does Tollens’ test work

Answer 8

Silver nitrate reacts with NaOH to precipitate silver oxide. This is then dissolved in ammonium hydroxide to form Ag(NH3)2 +. Silver is reduced and the aldehyde is oxidised.

Question 9

How are they reduced

Answer 9

BH4- or AlH4- can supply hydride ions. Acts as a nucleophile and attacks the delta positive carbon.

Question 10

Lithium aluminium hydride conditions

Answer 10

Reacts with water so dry inert solution (ether). Can happen at room temp since strong reducing agent. Must be hydrolysed with dilute acid to release alcohol from ion.

Question 11

Sodium borohydride conditions

Answer 11

Can happen in aqueous solution or methanol, needs warming, hydrolysed with dilute acid.

Question 12

Iodoform positive test

Answer 12

Yellow solid with antiseptic smell

Question 13

Iodoform reaction products

Answer 13

CHI3 and RCOO-

Question 14

Formula of grignard

Answer 14

RMgX, X = halogen and R = alkyl group

Question 15

What does a grignard act like?

Answer 15

R- nucleophile that acts electron deficient centres

Question 16

Formation of grignard

Answer 16

Haloalkane to granulated magnesium in ethersolvent. Set up reflux and warm with water bath.

Question 17

Grignard + aldehyde

Answer 17

R-MgBr + CH3CHO -> R–CH(CH3)OMgBr

R–CH(CH3)OMgBr + H2O -> R–CH(CH3)OH + Mg(OH)Br

Question 18

Addition of HCN to carbonyl

Answer 18

Can attack from above or below the trigonal plane.
Nucleophile attacks d+ carbon and heterolytic fission of pi bond with oxygen. Oxygen then negatively charged and is protonated

Question 19

Hydrolysis of nitriles

Answer 19

Converted to carboxylic acid when heated under reflux.
In acidic conditions, gives carboxylic acid and NH4+
In alkali conditions, gives carboxylate and NH3.

Question 20

Reaction of carboxylic acid to primary alcohols

Answer 20

With lithium aluminium hydride in dry ether (NaHBH4 is not reactive enough).
RCOOH + 4[H] -> RCH2OH + H2O
Must treat with dilute sulfuric acid at the end.

Question 21

Reaction of PCl5 with carboxylic acid

Answer 21

Gives acyl chloride and steamy fumes of HCl.
OH group replaced with Cl atom.
Can separate products with fractional distillation
CH3COOH + PCl5 -> Ethanoyl chloride + POCl3 + HCl

Question 22

Carboxylic acid react with ethanol with acid catalyst

Answer 22

Addition-elimination reaction, heat under reflux, slow and reversible, conc. sulfuric acid
Ethanoic acid takes proton from acid catalyst onto lone pair of O, positive charge then is delocalised and goes onto C.
Ethanol oxygen lone pair attacks C+.
Proton transfers within the molecule and molecule of water lost.
Hydrogen removed from oxygen to regenerate catalyst

Question 23

Acyl chloride with water

Answer 23

Makes carboxylic acid vigorous at room temp. HCl steamy fumes given off

1) Nucleophilic addition of water.
2) Elimination of Cl-
3) Deprotonation

Question 24

Acyl chloride with alcohol

Answer 24

Makes ester Cold reflux reaction. HCl steamy fumes

1) Addition of alcohol
2) Elimination of Cl-
3) Deprotonation

Question 25

Concentrated ammonia with acyl chloride

Answer 25

Ammonium chloride and amide formed. Cold reflux.
1) Nucleo addition: d+ carbon attacked by NH3.
2) Nucleo elim: C=O forms again and Cl- leaves.
3) Deprotonation by Cl- or NH3 to form NH4.
HCl reacts with NH3 to form NH4 also.

Question 26

Hydrolysis reaction of ester (acidic conditions)

Answer 26

Heat under reflux with dilute (to drive the equilibrium away from water towards products) sulfuric acid. Produce carboxylic acid and alcohol (can react together).

1) Ester takes a proton from hydroxonium to form a resonance structure. (+ve on C)
2) Water nucleophilic attack on carbon atom.
3) Proton transferred from bottom oxygen to oxygen with ethyl group
4) Ethanol lost
5) Deprotonation to carboxylic acid to regen catalyst

Question 27

Hydrolysis reaction of ester (alkaline conditions)

Answer 27

Heat under reflux, irreversible because OH is much greater nucleophile then alcohol of ester.

1) Nucleophilic addition OH attacks C.
2) Nucleophilic elimination of alkoxide
3) Deprotonation

Question 28

Why can’t lithal reduce alkene

Answer 28

Alkene has high e density on double bond, cannot be attacked, will not undergo nucleophilic addition

Question 29

Grignard reagent with CO2

Answer 29

Dry CO2 bubbled through grignard reagent in ether then dilute acid added that adds 1 carbon and makes carboxylic acid

Question 30

Grignard reagent with H2O

Answer 30

Produce alkane

Question 31

Iodoform reaction conditions

Answer 31

I2 and NaOH