Ch 12Aldehydes, Ketones and Carboxylic Acids — Class 12 Chemistry, concept-first.

The previous chapter dealt with organic compounds containing a carbon-oxygen SINGLE bond (alcohols, ethers).

Aldehydes, ketones and carboxylic acids are classified according to the nature of the carbon skeleton bonded to their carbonyl (or carboxyl) group.

Aldehydes are classified as aliphatic or aromatic depending on what their -CHO (formyl) group is attached to.

Ketones are likewise classified as aliphatic or aromatic. ALIPHATIC KETONES have the C=O group attached to two alkyl groups; general formula R-CO-R', where R and R' may be identical or different.

Carboxylic acids are classified as aliphatic or aromatic. ALIPHATIC CARBOXYLIC ACIDS (also called fatty acids) have the -COOH (carboxyl) group bonded to an alkyl group; general formula R-COOH, R = H o…

Having classified aldehydes, ketones and carboxylic acids by carbon skeleton in section 12.2, this section turns to how each family is actually named.

Aldehyde and carboxylic-acid names are closely related, and each family has both a TRIVIAL and an IUPAC naming system.

TRIVIAL NAMES of aliphatic ketones are built from the names of the two alkyl or aryl groups attached to the carbonyl carbon, written out in ALPHABETICAL order and followed by the word 'ketone' (e.g.

Having covered how aldehydes and ketones are classified and named, the chapter turns next to how they are actually made in the laboratory.

(a) By oxidation of alcohols: primary alcohols are oxidised to aldehydes, and secondary alcohols to ketones (this reaction itself was covered in Chapter 11); the oxidant used has to be a MILD, careful…

These further routes all start from one common functional group, yet give aldehydes and ketones by genuinely DIFFERENT specific reactions in each case.

Aliphatic or aromatic ESTERS can be reduced specifically to ALDEHYDES using diisobutylaluminium hydride, DIBAl-H (also written AlH(i-Bu)2): R-CO-O-R' with AlH(i-Bu)2, then H3O+ on workup, gives R-CHO…

Having covered how aldehydes and ketones are prepared (12.4), the chapter turns next to how carboxylic acids themselves are made.

Alkyl or aryl nitriles, on acid hydrolysis with a dilute mineral acid (dilute H2SO4 or dilute HCl), FIRST give an amide -- via a short-lived imine intermediate, R-C(=NH)-OH -- and that amide, on FURTH…

(a) Acyl chlorides, on hydrolysis with plain water, give carboxylic acids directly -- and this method works equally well for both aliphatic and aromatic acids: R-COCl + H2O gives R-COOH + HCl.

Carboxylic acids can be obtained from esters by EITHER of two hydrolysis routes. (a) ACID hydrolysis: an ester heated with a dilute mineral acid (dilute HCl or dilute H2SO4) gives the corresponding ca…

Aromatic carboxylic acids can be prepared by oxidising an alkylbenzene with dilute HNO3, or with alkaline or acidic KMnO4, or with chromic acid.

Carboxylic acids can also be prepared by oxidising alkenes with KMnO4 in dilute H2SO4: the alkene's C=C double bond is oxidatively CLEAVED apart, and each of the two alkene carbons ends up bearing its…

A Grignard reagent, dissolved in dry ether, is added to solid carbon dioxide (dry ice); this addition gives a magnesium-carboxylate complex, R-COOMgX, which on subsequent acid hydrolysis gives the cor…

Having covered how aldehydes, ketones and carboxylic acids are prepared (12.4-12.5), the chapter turns next to how these three families actually BEHAVE physically -- their physical state, boiling poin…

The carbonyl bond, C=O, present in both aldehydes and ketones, is a POLAR covalent bond (oxygen being considerably more electronegative than carbon).

Formaldehyde is a GAS at ordinary room temperature, with an irritating odour. Acetaldehyde is an extremely volatile, colourless LIQUID.

The oxygen atom of a carbonyl group, C=O, is able to take part in hydrogen bonding directly with a water molecule (Fig.

Lower aliphatic carboxylic acids, up to about nine carbon atoms, are colourless liquids with distinctly irritating odours; the higher homologues beyond that are instead colourless, odourless, wax-like…

The polarity of the carbonyl group originates from two combined effects: oxygen's higher electronegativity relative to carbon (a purely inductive effect), AND resonance effects specific to the C=O pi…

Reactivity of aldehydes and ketones toward nucleophiles traces directly back to the carbonyl-group polarity worked out in 12.7: the more electrophilic the carbonyl carbon, the more reactive the compou…

Having established, in 12.7, exactly WHY the carbonyl carbon of an aldehyde or ketone is chemically reactive (its electrophilic polarity), the chapter now works systematically through the actual chemi…

Aldehydes are easily oxidised on to carboxylic acids, and so themselves act as REDUCING agents toward mild oxidants; ketones, lacking any hydrogen directly on their carbonyl carbon, cannot be oxidised…

In every reaction catalogued in this section, a nucleophilic reagent attacks the positively-polarised, electrophilic carbonyl carbon set up in section 12.7 -- the section works systematically through…

(a) OXIDATION BY DILUTE HNO3, KMnO4 AND K2Cr2O7: aldehydes are oxidised straight through to the corresponding carboxylic acid by any of these three oxidants, provided the reaction medium is acidic --…

Aromatic aldehydes and ketones undergo the same broad family of electrophilic AROMATIC substitution reactions that any substituted benzene ring does -- specifically nitration, sulfonation, and halogen…

Having worked through the full chemistry of the carbonyl group in aldehydes and ketones (section 12.8), the chapter turns in its final major section to the characteristic chemistry of the -COOH group…

The carboxyl group, -COOH -- an -OH bonded directly to a carbonyl carbon -- is what gives carboxylic acids their genuinely acidic character.

Three distinct laboratory tests confirm the presence of a -COOH group in an unknown compound. (a) LITMUS TEST (valid specifically for water-SOLUBLE substances): an aqueous solution of a -COOH-containi…

Carboxylic acids, heated with any of three different reagents -- PCl3, PCl5, or SOCl2 (thionyl chloride) -- are converted to the corresponding ACYL CHLORIDE, the -OH of the original -COOH group being…

Carboxylic acids react with ammonia to give, first, an AMMONIUM CARBOXYLATE salt (R-COOH + NH3 gives R-COONH4); this ammonium salt, on FURTHER strong heating at high temperature, decomposes -- losing…

Monocarboxylic acids, heated with a strong DEHYDRATING agent -- either P2O5 or concentrated H2SO4 -- give ACID ANHYDRIDES: 2 R-COOH, with P2O5 and heat, gives (R-CO)2O + H2O.

The SODIUM salt of a carboxylic acid, heated together with soda lime (a mixture of sodium hydroxide and calcium oxide, CaO), undergoes DECARBOXYLATION -- it loses its carboxyl carbon entirely, as sodi…

Carboxylic acids are reduced through to PRIMARY ALCOHOLS by the powerful reducing agent lithium aluminium hydride (LiAlH4), carried out in dry ether solvent: R-COOH, with LiAlH4/dry ether, gives R-CH2…

The end-of-chapter questions of this group, exactly as the book prints them.

The end-of-chapter questions of this group, exactly as the book prints them.

The end-of-chapter questions of this group, exactly as the book prints them.

The end-of-chapter questions of this group, exactly as the book prints them.

The end-of-chapter questions of this group, exactly as the book prints them.

Sample papers and previous-year board questions for this subject.