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NCERT Class 12 Chemistry chapter 12 notes discusses the chapter Aldehydes, Ketones and carboxylic acids. This article will provide a quick overview of the chapter. These short notes are useful for CBSE Class 12 board examinations and strictly follows most recent CBSE Syllabus.
NCERT Class 12 Chemistry chapter 12 notes discusses about structure of carbonyl group, preparation of aldehydes, preparation of ketones. CBSE Class 12 Chemistry chapter 12 notes also includes physical properties of aldehydes and ketones and discusses some of the important chemical reactions of aldehydes and ketones. Aldehydes, ketones and carboxylic acid Class 12 notes gives idea about structure of carboxyl group, preparations of carboxylic acid. Physical properties, and chemical reactions of carboxylic acid are also explains in notes for class 12 chemistry chapter 12 etc.
Students can refer to Class 12 Chemistry revision notes solution chapter 12 for a more details of these concepts. This chapter is part of organic chemistry, which can be confusing and daunting at first. Students can learn more about these subjects by reading the CBSE Class 12 Chemistry revision notes solution chapter 12.
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Aldehydes, ketones, carboxylic acids, and their derivatives are organic compounds with the carbonyl group (CO) as the functional group. These are referred to as carbonyl compounds together. The carbonyl group's oxygen atom is significantly more electronegative than the carbon atom. As a result, the oxygen atom attracts the electron cloud of the -bond towards itself, resulting in an unsymmetrical -electron cloud of >C = O. As a result, carbonyl carbon has a positive charge while carbonyl oxygen has a negative charge. Thus the carbonyl group is polar. In aldehydes one hydrogen and an alkyl/aryl group is attached to carbonyl group. But in ketone two alkyl/aryl groups are attached to carbonyl group.
According to CBSE Class 12 Chemistry chapter 12 notes, preparation of aldehydes is given by:
By oxidation of alcohols
Aldehydes are formed when primary alcohols are oxidized in the presence of an oxidizing agent such as K2Cr2O7 / H2SO4, KMnO4, or CrO3
By dehydrogenation of alcohols
Aldehyde is formed when primary alcohol vapours pass over heated copper or silver at 573 K.
By Rosenmund reduction
Aldehyde is produced by hydrogenating acyl chloride over palladium on barium sulphate.
By Stephen’s reaction
When nitriles are reduced in the presence of stannous chloride and HCl, an imine is formed, which when hydrolyzed yields the corresponding aldehyde.
RCN + SnCl2 + HCl → RCH=NH + H3O+→ RCHO
From nitriles and esters
DIBAL-H (Diisobutylaluminium Hydride) preferentially reduces nitriles and esters to aldehydes.
RCN AlH(i-Bu)2,H2O→ RCHO
CH3(CH2)9-CO-OC2H5 + DIBAL-H→ CH3(CH2)9-CHO
By oxidation of methylbenzene (Etard reaction)
Chromyl chloride converts the methyl group to a chromium complex, which when hydrolyzed yields the benzaldehyde.
With chromic oxide
n the presence of chromic oxide, toluene or substituted toluene is converted to benzaldehyde in acetic anhydride.
By sidechain chlorination followed by hydrolysis
By Gattermann-Koch reaction
Benzaldehyde or substituted benzaldehydes are produced by treating benzene or its derivatives with carbon monoxide and HCl in the presence of anhydrous aluminium chloride or cuprous chloride (CuCl).
According to Aldehydes, ketones and carboxylic acid Class 12 notes and class 12 Aldehydes, ketones and carboxylic acid notes, the preparation of ketones is given by:
From acyl chlorides
Acyl chloride is converted to ketone when it is treated with dialkyl cadmium (made by reacting cadmium chloride with Grignard reagent).
2 R-Mg-X + CdCl2 → R2Cd+2 MgXCl
2 R’-CO-Cl + R2Cd → 2 R’-CO-R + CdCl2
From nitriles
Nitriles are converted to ketones after being treated with Grignard reagent and then hydrolyzed.
From benzene or substituted benzene
Ketone is formed when benzene or substituted benzene is treated with acid chloride in the presence of anhydrous aluminium chloride.
At room temperature, methane is a gas. Ethanol is a very flammable liquid. At room temperature, other aldehydes and ketones are liquid or solid.
Boiling points are greater than hydrocarbons and ethers of comparable molecular weights. This is because of weak molecular association in aldehydes and ketones due to the dipole-dipole interactions. Due to the lack of H-bonding, their boiling points are lower than those of alcohols.
Because they form H-bonds with water, lower aldehydes and ketones like methanal, ethanal, and propanone are miscible with water in all proportions.
Lower aldehydes have a harsh, pungent odour. The odour gets less strong and more delicate as molecular mass increases.
NCERT notes for Class 12 Chemistry chapter 12 explain the chemical reactions as:
Nucleophilic addition reactions
The hybridization of C shifts from sp2 to sp3 when a nucleophile attacks the carbonyl carbon. Due to steric and electrical reasons, aldehydes are more sensitive to nucleophilic addition processes than ketones.
Addition of hydrogen cyanide
Addition of sodium hydrogensulphite
Addition of alcohols
Addition of ammonia and its derivatives
Reduction
Reduction of alcohols
Sodium borohydride or lithium aluminium hydride, as well as catalytic hydrogenation, reduce aldehydes and ketones to primary and secondary alcohols, respectively.
Reduction of hydrocarbons
When aldehydes and ketones are treated with zinc amalgam and strong hydrochloric acid, the carbonyl group is reduced to CH2,(Clemmensen reduction)
On treating carbonyl compound with hydrazine followed by sodium or potassium hydroxide in a high boiling solvent such as ethylene glycol reduces the carbonyl group of aldehydes and ketones to CH2 (Wolff-Kishner reaction)
Oxidation
Oxidation reactions of aldehyde and ketones are different
Aldehydes and ketones can be distinguished using the 2 reactions below because aldehydes are easier to oxidize than ketones.
Tollen’s test
A bright silver mirror is formed by heating an aldehyde with freshly made ammonical AgNO3 solution (Tollen's reagent).
RCHO + 2 [Ag(NH3)2]+ + 3 OH- → RCOO- + 2 Ag + 2 H2O + 4 NH3
Fehling’s test
A reddish-brown precipitate is formed when an aldehyde is heated with Fehling reagent.
R-CHO + 2 Cu2+ + 5 OH- → 2 ROO-+ Cu2O + 3 H2O
Oxidation of methyl ketone by haloform reaction
This test is positive for all carboxyl compounds with the – COCH3 group.
Reactions due to α-hydrogen
Because of the strong electron-withdrawing impact of the carbonyl group and the resonance stabilization of the conjugate base, -hydrogens in aldehydes and ketones are acidic in nature.
Aldol condensation
In the presence of dil. alkali, aldehydes and ketones with at least one -hydrogen undergo Aldol Condensation to create β-hydroxy aldehydes (aldol) or β-hydroxy ketones [ketol].
Cross Aldol condensation
Cross aldol condensation occurs when aldol condensation occurs between two separate aldehydes and/or ketones.
Other reactions
Cannizzaro reaction
When aldehydes without -hydrogen atom are treated with strong alkali, they undergo self-oxidation and reduction (disproportionation) reactions, resulting in alcohol and acid salt.
Electrophilic substitution reaction
Electrophilic substitution reactions occur at the ring of aromatic aldehydes and ketones, while the carbonyl group serves as a deactivating and meta-directing group.
The carboxylic carbon is less electrophilic due to the potential resonance configuration depicted below. The carbonyl carbon and the carboxylic carbon bonds are then aligned in the plane and separated by 120°.
From primary alcohols and aldehydes
From alkyl benzenes
Aromatic carboxylic acids are made by oxidizing alkyl benzenes with chromic acid or acidic or alkaline potassium permanganate at high temperatures.
From nitriles and amides
When nitriles are hydrolyzed in the presence of dilute acids or bases, an amide is formed, which can then be further hydrolyzed to produce carboxylic acid.
From Grignard reagent
Grignard reagents react with carbon dioxide (dry ice) to produce carboxylic acid salts, which are then hydrolyzed to produce carboxylic acids.
From acyl halides and anhydrides
When acid chlorides are hydrolyzed with water, carboxylic acids are formed. Carboxylate ions are generated during basic hydrolysis, which are then acidified to form carboxylic acids. When anhydrides are hydrolyzed, the corresponding acid is produced
From esters
Basic hydrolysis of esters produces carboxylates, which are acidified to produce corresponding carboxylic acids. Acidic hydrolysis of esters directly produce corresponding carboxylic acids.
Because the non-polar component of the acid increases as the size of the alky group increases, the solubility of carboxylic acid decreases. Carboxylic acids boil at a higher temperature than aldehydes, ketones, or even alcohols with similar molecular weights. This is due to significant intermolecular hydrogen bonding between carboxylic acid molecules.
Acidity
Reaction with metals
2 RCOOH + 2 Na → 2 R-COO-Na+ + H2
R-COOH + NaOH → 2 R-COO-Na+ + H2O
R-COOH + NaHCO3 → 2 R-COO-Na+ + H2O + CO2
Carboxylic acid dissociates in water to yield the carboxylate anion and the hydronium ion, which are both resonance-stabilized.
Effects of substituents on carboxylic acid acidity: Electron withdrawing groups increase carboxylic acid acidity by stabilizing the conjugate base by delocalization of the negative charge via inductive and/or resonance effects. Electron-donating groups, on the other hand, reduce acidity by destabilizing the conjugate base.
Reactions involving cleavage of C-OH bond
Formation of anhydride
Esterification
In the presence of a mineral acid such as concentratedH2SO4 or HCl gas as a catalyst, carboxylic acids are esterified with alcohols.
RCOOH + R’OH (acidic medium) ↔ RCOOR’ + H2O
Reactions with PCl3, PCl5 and SOCl2
RCOOH + PCl5 → RCOCl + POCl3 + HCl
3 RCOOH + PCl3 → 3 RCOCl + H3PO3
RCOOH + SOCl2 → RCOCl +SO2 + HCl
Reaction with ammonia
Reactions involving -COOH group
Reduction
In the presence of LiAlH4 or B2H6, carboxylic acids are reduced to alcohols.
Decarboxylation
Heating sodium or potassium salts of carboxylic acids with soda lime (NaOH + CaO in a 3:1 ratio) produces hydrocarbons with one less carbon than the parent acid.
Substitution reactions in the hydrocarbon part
Halogenation (Hell-Volhard-Zelinsky reaction)
Carboxylic acids containing α -hydrogen are halogenated at the α-position with chlorine or bromine in the presence of a small amount of red phosphorus to produce α-halocarboxylic acids).
Ring substitution
Electrophilic substitution reactions occur in aromatic carboxylic acids. In benzoic acid, the carboxyl group is an electron withdrawing and meta directing group.
These topics are included in Class 12 Chemistry chapter 12 notes pdf download and Aldehydes, ketones and carboxylic acid Class 12 pdf download.
Significance of NCERT Class 12 Chemistry Chapter 12 Notes
To attempt and answer problems in the chapter "Aldehydes, Ketones, and Carboxylic Acids," a good understanding of concepts is required. The key topics in Aldehydes, ketones and carboxylic acid Class 12 notes have been fractured to help students better study and comprehend the subjects. The chapter is adorned with concepts, equations, and the answers are written under expert supervision.
NCERT notes for Class 12 Chemistry chapter 12 provides an overview of the main topics of Class 12 CBSE Chemistry Syllabus . NCERT notes for Class 12 Chemistry chapter 12 definitely help students for the preparation of competitive exams like VITEEE, BITSAT, JEE Main, NEET etc. Class 12 Chemistry chapter 12 notes pdf download can be used to prepare in offline mode. By downloading Aldehydes, ketones and carboxylic acid Class 12 pdf download student can study in their convenient time.
Ans- Rosemund’s Reduction Reaction, Etard reaction, Wolf-Kishner Reaction, Clemmenson’s Reduction Reaction , Cannizzaro Reaction, Gatterman-Koch reaction, Hell-Volhard Zelinsky Reaction etc are discussed in Class 12 Aldehydes, ketones and carboxylic acid notes?.
Ans-. Aldehydes and ketones are widely used as solvents. Formalin is used to preserve biological specimens. Many aldehydes are used in drugs and polymers. Many ketones are well known for their flavours and odours .These are discussed in NCERT Class 12 Chemistry chapter 12
Ans- Aldehydes are chemical molecules with a carbonyl group linked to a hydrogen atom and an alkyl group.Ketones are chemical molecules that have a carbonyl group linked to two alkyl groups. Carboxylic acids are hydrocarbon molecules in which the carboxyl group replaces one or more hydrogen atoms in the hydrocarbon..
Ans- Carbonyl group is a functional group present in both aldehydes and ketones. The hydrogen of the hydroxyl group is ionizable in carboxylic acids because of their weak nature. A carboxyl group is found in carboxylic acids. The carbonyl group is at the end and in the centre of aldehydes and ketones, respectively. The carboxyl functional group is designated by the letter -CO, while the carboxyl group is marked by the letter -COOH.
Ans- 37% aqueous solution of formaldehye is called formalin.
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As per latest 2024 syllabus. Physics formulas, equations, & laws of class 11 & 12th chapters
As per latest 2024 syllabus. Chemistry formulas, equations, & laws of class 11 & 12th chapters
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