This chapter focuses on the study of aldehydes, ketones, and carboxylic acids, which are crucial functional groups in organic chemistry.
Aldehydes, Ketones and Carboxylic Acids – Formula & Equation Sheet
Essential formulas and equations from Chemistry - II, tailored for Class 12 in Chemistry.
This one-pager compiles key formulas and equations from the Aldehydes, Ketones and Carboxylic Acids chapter of Chemistry - II. Ideal for exam prep, quick reference, and solving time-bound numerical problems accurately.
Key concepts & formulas
Essential formulas, key terms, and important concepts for quick reference and revision.
Formulas
RCHO (General formula for Aldehydes)
R is an alkyl or aryl group, and the functional group is –CHO. Aldehydes are characterized by having at least one hydrogen atom attached to the carbonyl carbon.
RC(=O)R' (General formula for Ketones)
R and R' represent alkyl or aryl groups. This formula indicates that ketones have the carbonyl group (C=O) between two carbon atoms.
RCOOH (General formula for Carboxylic Acids)
R represents an alkyl or aryl group, and –COOH is the carboxyl group. Carboxylic acids contain the functional group that gives acidity.
pK_a = -log(K_a)
Where K_a is the acid dissociation constant. This equation indicates how the strength of an acid is measured; smaller pK_a values represent stronger acids.
C_nH_(2n)O (General formula for unsaturated aldehydes)
For n > 1, this formula represents the general structure of unsaturated aldehydes leading to their reactivity.
1. Oxidation of Alcohols: RCH₂OH + [O] → RCHO + H₂O
Primary alcohols are oxidized to form aldehydes using oxidizing agents.
2. Ozonolysis of Alkenes: RCH=CHR' + O₃ → RCHO + R'CHO
Ozonolysis cleaves double bonds and produces aldehydes or ketones depending on the alkene structure.
Aldol Reaction: 2 RCHO + NaOH → RCH(OH)CH₂CHO (Aldol) → RCH=CHCHO + H₂O (Aldol Condensation)
This reaction describes how aldehydes with α-hydrogens react in the presence of base to form β-hydroxyaldehydes (aldols).
Cannizzaro Reaction: RCHO + KOH (conc) → RCOOK + RCH₂OH
Aldehydes without α-hydrogens undergo disproportionation into a carboxylate and an alcohol under strong basic conditions.
Reduction: RCHO + H₂ (Pd) → RCH₂OH
Reduction of aldehydes to primary alcohols can be achieved through hydrogenation using catalysts.
Equations
Tollens' Test: RCHO + Ag(NH₃)₂OH → RCOO⁻ + Ag↓ + NH₃ + H₂O
A positive Tollens' test indicates the presence of aldehydes, yielding metallic silver as a mirror on the reaction vessel.
Fehling's Test: RCHO + Cu²⁺ → RCOO⁻ + Cu₂O (red precipitate)
This test distinguishes aldehydes from ketones; the formation of a red precipitate indicates an aldehyde.
Halogenation: RCOOH + Br₂ → RCOBr + HBr
The reaction of carboxylic acids with halogens to form acyl halides under specific conditions.
Formation of Esters: RCOOH + R'OH ⇌ RCOOR' + H₂O
Carboxylic acids react with alcohols to form esters in a reaction known as esterification.
DIBAL-H Reduction: RCOOR' + DIBAL-H → RCHO + R'H →
Diisobutylaluminium hydride (DIBAL-H) selectively reduces esters to aldehydes.
Reducing Aldehydes: RCHO + LiAlH₄ → RCH₂OH
Aldehydes are reduced to primary alcohols using lithium aluminium hydride.
Formation of Imine: RCHO + R'NH₂ ⇌ RCH=NHR' + H₂O
The reaction between an aldehyde (or ketone) and an amine yields an imine through condensation.
Formation of Acetals: RCHO + 2 R'OH ⇌ RCH(OR')₂ + H₂O
Aldehydes react with alcohols to form acetals in the presence of acid catalysts.
Carboxylic Acid Formation: RCHO + [O] (mild) → RCOOH
Aldehydes can be oxidized into carboxylic acids using mild oxidizing agents.
Wolff-Kishner Reduction: RCHO + H₂N-NH₂ → R + N₂ + H₂O
This reaction reduces aldehydes or ketones to alkanes using hydrazine and strong base.
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