31 Year NEET Previous Year Questions: Aldehydes, Ketones & Carboxylic Acids - 3 - NEET MCQ

Aldehydes containing no α-hydrogen atom on warming with 50% NaOH or KOH undergo disproportionation i.e. self oxidation -reduction known as Cannizzaro’s reaction

Formalin is an aqueous solution (40%) of formaldehyde.

An electron releasing substituent (+I effect) intensity the negative charge on the anion resulting in the decrease of stability and thus decreases the acidity of the acid. Hence acidic character decreases as the + I-effect of the alkyl group increases as

CH₃ < CH₃CH₂ < CH₃CH₂CH₂
< CH₃CH₂CH₂CH₂
Hence the order of acidic strength becomes:
(i) > (ii) > (iii) > (iv)

Chlorine is electron withdrawing group.
Further Inductive effect is stronger at α
position than β-position. i.e.,

Acetone forms mesitylene (1,3,5-trimethyl benzene) on distillation with conc. H₂SO₄.

When 3 molecules are combined in presence of dry HCl gas they condense to form phorone.

Note : Two molecules of acetone condense to form mesityl oxide.

 I₂ and NaOH react with acetophenone
(C₆H₅COCH₃) to give yellow ppt. of CHI₃ but benzophenone (C₆H₅COC₆H₅) does not and hence can be used to distinguish between them. Oxidation of methyl ketones with sodium Hypoiodite (NaOI) or (I₂ +NaOH) gives iodoform (CHI₃) but not in case of benzophenone.

Acetaldehyde reacts only with nucleophiles. Since the mobile p electrons of carbon– oxygen double bond are strongly pulled towards oxygen, carbonyl carbon is electrondeficient and carbonyl oxygen is electronrich.
The electron deficient (acidic) carbonyl
carbon is most susceptible to attack by
electron rich nucleophilic reagents, that is, by base. Hence the typical reaction of aldehydes and ketones is nucleophilic
addition.

Ketones on oxidation give carboxylic acids with lesser number of carbon atoms, i.e.,

Among acetic acid, phenol and n-hexanol only CH₃ COOH reacts with NaHCO₃ to evolve CO₂ gas.

Chromic acid and KMnO₄ will cleave the molecule at the site of double bond while Cu at 300°C cannot oxidise COCH3 COOH. The only reagent suitable for this conversion is NaOI or NaOH + I₂ (iodoform
test):

Pinacolone is 3,3-dimethyl-2 butanone.

When benzaldehyde is refluxed with aqueous alcoholic potassium cyanide, two molecules of benzaldehyde condense together to form benzain

Dihydrogen sodium phosphate (NaH₂PO₄) does not have a lone pair of electrons on the P atom. As such it can not act as a nucleophile and hence does not react with aldehydes and ketones.

Aldehydes which contain a α -hydrogen on a saturated carbon, i.e., CH₃CH₂CHO undergo aldol condensation.

When glycerol is heated with oxalic acid
following reaction occurs.

Claisen condensation: Intermolecular
condensation of esters containing α-
hydrogen atom in presence of strong base to form β-keto ester

The function of NaOH is
(i) To convert phenol to more stronger
nucleophile PhO^–
(ii) To neutralize the acid formed

Methyl acetate and ethyl acetate on
hydrolysis give CH₃COOH which is a liquid. Similarly ethyl formate on hydrolysis will give formic acid which is also a liquid. Only ethyl benzoate on hydrolysis will give benzoic acid
which is a solid.

Thus acetone reacts with iodine to form
iodoform in the presence of NaOH.