carbonyls and carboxylic acids

Question 1

What is made when aldehydes are oxidised?

Answer 1

Carboxylic acids

Question 2

What conditions are needed for the oxidation of aldehydes?

Answer 2

acidified dichromate ions (H⁺ and Cr₂O₇²⁻)
Made from:
-Sulfuric acid H₂SO₄
-Potassium dichromate K₂Cr₂O₇

Question 3

what is the carbonyl group?

Answer 3

Carbon double bonded to oxygen. C=O.

Question 4

Why why does the carbonyl group react with nucleophiles?

Answer 4

• Oxygen in more electronegative than carbon in the C=O bond.
  -Making electron density lie closer to oxygen than carbon.
  -This produces a slightly positive charge on the carbon, and a slightly negative charge on the oxygen, making the molecule polar.
  -The polarity of the molecule allows it to react with nucleophiles, as they will be attracted to the σ+ carbon.

Question 5

What is used to reduce carbonyl compounds?

Answer 5

Sodium tetrahydradridoborate
NaBH₄
Hydrogen cyanide
HCN

Question 6

draw the mechanism for the reduction of a ketone by NaBH₄

Answer 6

look it up (remeber to include a electro positive proton removed from water)

Question 7

what is made when ketones are reduced using NaBH₄

Answer 7

Secondary alcohols

Question 8

What is produced when aldehydes are reduced using NaBH₄

Answer 8

Primary alcohols

Question 9

What is produced when carbonyls are reduced using HCN?

Answer 9

Hydroxynitriles

Question 10

Draw the mechanism for the reduction of carbonyls by HCN

Answer 10

look it up

Question 11

what is the nucleophile in the reduction of nitriles by NaBH₄

Answer 11

H- ion
hydrogen ion

Question 12

What is the nucleophile in the reduction of carbonyls by HCN

Answer 12

CN- (cyanide ion)

Question 13

Sunce hydrogen cyanide is highly poisonous, what two compounds are used to produce it safely in a laboratory?

Answer 13

sulfuric acid and sodium cyanide

Question 14

What is brady’s reagent and what does it test for?

Answer 14

Brady’s reagent is a solution of 2,4 dinitrophenylhydrazine dissolved in methanol with sulfuric acid.
It is used to test for carbonyl groups, producing an orange precipitate if (aldehydes and ketones) are present.

Question 15

What is Tollens reagent and what does it test for?

Answer 15

Tollens reagent is a solution of silver nitrate in aqueous ammonia.
It is used to test for aldehydes, producing a silver mirror if an aldehyde is present.

Question 16

Explain how an aldehyde or ketone be identified after both brady’s and tollen’s reagents

Answer 16

The precipitate fromed from the reaction of the carbonyl with 2,4 DNP is filtered so that just the solid remains.
The solid is then recrystallised to produce a pure solid.
This melting point of the solid is then measured and compared to to a database of 2,4 DNP derivatives.

Question 17

Briefly describe the steps used to fully identify a carbonyl compound.

Answer 17

• Brady’s reagent to find out if the substance contains a carbonyl group (ketone or aldehyde.
• Tollens reagent is then used to find out if the substance is a aldehyde.
• The precipitate fromed from the substances reaction with 2,4 DNP is then filtered and recrystallised, and its melting point compared

Question 18

Why are carboxylic acids soluable?

Answer 18

Carboxylic acids conatain an O-H and a C=O (making the carboxylic acid polar) which engages in hydrogen benoding between water.

Question 19

What happens to the solubility of carboxylic acids as chain legth increases and why?

Answer 19

Solubility of carboxylic acids decrease as the polarity of the O-H and C=O bonds have less of an effect on the overall molecule, decreasing the molecules overall polarity and solubility.

Question 20

Are carboxylic acids strong or weak acids?

Answer 20

Weak

Question 21

What salt is produced in neutralisation of carboxylic acids and carboxylic acids reactions with metals?

Answer 21

Carboxylate salts
(carboxylate ion and metal ion)
CH3COO- Na+