Tiêu đề SP-3_Ch-18_Aldehydes, Ketones and Carboxylic Acids.pdf ✅

Chapter Contents Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Chapter 18 Aldehydes, Ketones and Carboxylic Acids  Introduction  Nomenclature and Structure of Carbonyl Group  Methods for Preparation of Aldehydes and Ketones  Physical Properties of Aldehydes and Ketones  Chemical Reactions of Aldehydes and Ketones  Uses of Aldehydes and Ketones  Carboxylic Acids  Methods for Preparation of Carboxylic Acids  Physical Properties of Carboxylic Acids  Chemical Properties of Carboxylic Acids  Chapter in Daily Life  Some Important Name Reactions Introduction This chapter includes knowledge of carbonyl compounds i.e., the compounds containing C O as functional group. In this we study aldehydes, ketones, carboxylic acids and their derivatives. In aldehydes carbonyl group is attached to either two H-atoms or one R- or Ar-group and one H-atom. In ketones carbonyl group is attached to two alkyl or aryl groups. If both the groups are similar then this is a simple ketone but if both the groups are different it is a mixed ketone. O C R H Aldehyde (R- may be H- or alkyl or aryl group) O C R R Simple ketone (Both R-groups are alkyl or both aryl groups) O C R R' Mixed ketone (Both R-groups are different) The carbonyl compounds in which carbonyl group is attached to an –OH group, are called carboxylic acids i.e., O C R OH, where R- can be H-, alkyl or aryl-group. The compounds in which –OH group of carboxylic acid is replaced by other groups such as –X, –OR, –OCOR, –NH2 etc. are called acid derivatives. All these derivatives form carboxylic acid again on hydrolysis. O C R x –OH +x Acid halide or acylhalide O C R O –OH Acid anhydride –OH +OR' Ester (R- & R'- may or may not be same) –OH –NH2 Acid amide O O C R O C R OR' O C R NH2 O C R OH + +
234 Aldehydes, Ketones and Carboxylic Acids NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 NOMENCLATURE AND STRUCTURE OF CARBONYL GROUP Nomenclature (1) Aldehydes: The common names of most aldehydes are derived by replacing suffix ‘ic’ of acid from the name of carboxylic acid by “aldehyde”. Location of substituents on the carbon chain is indicated by Greek symbols i.e., , , ,  etc. –CHO is considered functional group and carbon atom adjacent to this is taken as -carbon and so on. IUPAC names of aldehydes are given as alkanals and their names are written by replacing suffix ‘e’ of alkane by ‘al’. In case of aldehydes the longest carbon chain is numbered starting from carbon of aldehydic group. CH CHO 3 Acetaldehyde ethanal Common name IUPAC name CHO Benzaldehyde CH Br  CH2 C O CH3 H   -Bromobutyraldehyde 3-Bromobutanal CH —CH—CHO 3 -Methyl propionaldehyde 2-Methylpropanal Common name IUPAC name OH Salicyldehyde O-Hydroxybenzaldehyde CH3 CHO When –CHO group is attached on a cyclic compound a suffix carbaldehyde is added at the end of the name of compound. CH CH —CH ==CH—C—H 3 2 Cyclohexanecarbaldehyde Pent-2-enal CHO O CHO Cyclobutanecarbaldehyde (2) Ketones: Common names of ketones are derived by naming two alkyl or aryl groups bonded to the carbonyl group. Location of substituents always starts from the adjacent carbon of carbonyl group i.e., ,  and so on. Some of the ketones have common popular names. In IUPAC system ketones are named as "alkanones" and their name is formed by replacing suffix ‘e’ of alkane by another suffix ‘one’. All acid derivatives are also called acyl derivatives. Aldehydes, ketones, carboxylic acids and their derivatives are widely spread in living organisms. They play important role in biological processes. Many of them are natural fragrance and flavour-producing substances such as Vaniline (obtained from vanilla beans) Salicyldehyde (obtained from meadow sweet) Cinnamaldehyde (obtained from cinnamon) Isoamylacetate (obtained from banana) OH OCH3 CHO Vaniline CHO OH Salicyldehyde CH = CH – CHO Cinnamaldehyde C O O CH CH 2 2 CHCH3 CH3 CH3 Isoamylacetate These compounds are used to add flavours to many food products and pharmaceuticals. Many carbonyl compounds are used for manufacturing many adhesives paints, perfumes, adhesives plastic fibres, resins etc. Acetone and acetic acid are used widely as solvents in laboratory as well as industries.
NEET Aldehydes, Ketones and Carboxylic Acids 235 Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 In case of bigger ketones having substituents present on them numbering of ‘C’ chain always starts from the end from where O || —C— group must attain the lowest possible number while naming the compound and names of different substituents are given in alphabetical order (prefixed by their locants) For cyclic ketones, carbonyl carbon is numbered one. CH — C—CH 3 3 O Acetone Propanone Acetophenone Phenylethanone O C CH3 Propiophenone Phenyl propanone O C CH2 CH3 Common name IUPAC name Diphenylmethanone Benzophenone O C 3-Methylcyclohexanone O CH3 To understand the naming more effectively let us have a few more examples. Examples: Formula Common name IUPAC name HCHO Formaldehyde Methanal 3 3 CH CHCHO | CH  Isobutyraldehyde 2-Methylpropanal 2 3 2 NO | CH CH CH CHO   -Nitrobutyraldehyde 2-Nitrobutanal CH2 = CH – CHO Acrolein Prop-2-enal CHO CHO Phthaldehyde Benzene-1, 2-dicarbaldehyde CH3CH = CH – CHO Crotonaldehyde But-2-en-1-al CH = CH.CHO Cinnamaldehyde 3-Phenylprop-2-en-1-al 3 2 2 3 O || CH CH — C— CH CH Diethylketone Pentan-3-one 3 3 3 3 CH CH O | || | CH — CH — C— CH — CH Diisopropylketone 2,4-Dimethylpentan-3-one O CH3 -Methylcyclohexanone 4-Methylcyclohexanone
236 Aldehydes, Ketones and Carboxylic Acids NEET Aakash Educational Services Limited - Regd. Office : Aakash Tower, 8, Pusa Road, New Delhi-110005 Ph. 011-47623456 Structure of the Carbonyl Group Carbon atom of carbonyl group is sp2 hybridised having triangular planar geometry. Carbon atom forms three sigma bonds and one (pi) bond, out of which 3 bonds are located in the same plane whereas fourth  bond, which is formed by lateral or sideways overlapping, is situated above and below the plane. Bond angles are approximately 120°. C 120° C O 120° O sp2 sp2  bond Carbonyl group is polarised due to difference in electronegativity between carbon and oxygen. Oxygen being more electronegative pulls the shared pair of electrons more towards itself making oxygen as a nucleophilic centre and carbon as an electrophilic centre. Hence carbonyl compounds have substantial dipole moment and their polarity can be expressed on the basis of resonance. C O C O– + Isomerism in aldehydes and ketones Following types of isomerism are shown by these compounds. 1. Chain Isomerism: Aldehydes having 4 or more carbon atoms and ketones having 5 or more carbon atoms show chain isomerism. Ex. (a) C4H8O : 322 Butanal CH CH CH CHO and 3 3 2-Methylpropanal CH | CH CH — CHO (b) C5H10O : 3 2 2 3 Pentan-2-one O || CH — C— CH CH CH and 3 3 3 3-Methylbutan-2-one O || CH C— CH — CH | CH 2. Position Isomerism: In which isomers differ in position of carbonyl group (not shown by aliphatic aldehydes) Ex. (a) C5H10O : 3 2 2 3 Pentan-2-one O || CH — C— CH CH CH and 32 23 Pentan-3-one O || CH CH C— CH CH (b) CHO CHO Benzene-1,2-dicarbaldehyde CHO CHO Benzene-1,3-dicarbaldehyde CHO CHO Benzene-1,4-dicarbaldehyde and 3. Functional Isomerism: Aldehydes and ketones (having 3 or more carbon atoms) can show functional isomerism. Ex. C3H6O, CH3CH2CHO, 3 3 O || CH — C— CH 4. Metamerism: Ketones show metamerism in which isomers have different alkyl groups around carbonyl group. Ex. CH3CH2COCH2CH3 and CH3CH2CH2COCH3