Carbonyls

Question 1

boiling points and solubility of carbonyls

Answer 1

•boiling point:
-increase with molecular mass
-higher than corresponding alkanes, lower than corresponding alcohols
•solubility: solubility decreases as molecule gets heavier bc they become more non polar

Question 2

what do aldehydes and ketones oxidise to?

Answer 2

•aldehydes = carboxylic acids (RCHO + [O] —> RCOOH)
•ketones = carboxylic acids with fewer carbons
*aldehydes are EASILY oxidised, ketones need POWERFUL oxidising agents under VIGOROUS conditions

Question 3

3 ways to test for aldehydes (oxidation)

Answer 3

1. ACIDIFIED K2Cr2O7 —> orange to green (Cr3+) OR MnO4- —> purple to colourless (Mn2+)
2. TOLLENS REAGENT (ammoniacal silver nitrate) —-> silver mirror (on warming- Ag)
3. BENEDICTS REAGENT/FEHLINGS SOLUTION —> brick red ppt ONLY FOR ALIPHATIC ALDEHYDES (on warming- Cu(I))

Question 4

describe the iodoform test

Answer 4

• when an alkaline solution of iodine is warmed with beta hydroxy/keto compound, a yellow pot of triiodomethane (CHI3) will form.
•reactions:
1. B hydroxy oxidised to B keto
2. methyl group next to B keto undergoes substitution with iodine
3. nucleophilic addition produces CHI3

Question 5

what are C=C, C=O, and C(triple bond)N reduced to and by what?

Answer 5

• C=C —> CH-CH reduced by H2
• C=O —> CH-OH reduced by H2 or H-
• C(triple bond)N —> CH-NH2

Question 6

why can’t H- reduce a C=C bond?

Answer 6

C=C is non polar and is electron dense so is not attacked by nucleophile H-

Question 7

what are the conditions and mechanism of reduction with NaBH4/LiAlH4?

Answer 7

conditions are aq or alcoholic solution, and follows a nucleophillic addition mechanism (so H- ions, therefore cant reduce C=C bonds)

Question 8

what do aldehydes and ketones get reduced to?

Answer 8

• aldehydes —> 1° alcohols

* ketones —> 2° alcohols

Question 9

what are the conditions and mechanism of reduction with H2?

Answer 9

nickel/platinum catalyst, hydrogenation/reduction

Question 10

explain how hydroxynitriles are formed from carbonyls

Answer 10

• nucleophilic addition

* carbonyl mixed with aq/alc solution of NaCN/KCN at room temp - nucleophile is the CN- (cyanide ion)

Question 11

what are advantages of nucleophilic addition?

Answer 11

• produces an organic product with longer carbon chain
• hydroxynitrile is easy hydrolysed to a carboxylic axis by heating with HCl
• production of optical isomers - one of which may produce a desired biological response