THE CHEMISTRY OF ALDEHYDES AND KETONES By Dr. Nahed Nasser

CONTENTS Bonding in carbonyl compounds Structural differences between aldehydes and ketones Drawing aldehydes and ketones Nomenclature of aldehydes and ketones Physical properties of aldehydes and ketones Preparation of aldehydes and ketones Reactions of adehydes and ketones ALDEHYDES & KETONES

CARBONYL COMPOUNDS Carbonyl compounds contain CO group, they include aldehydes, ketones, acids and acid derivatives Bonding the carbon is sp 2 hybridised and formsthree sigma (s) bonds the unhybridised 2p orbital of carbon is overlaps with a 2p orbital of oxygen to form a pi (  ) bond as oxygen is more electronegative than carbon the bond is polarized PLANAR WITH BOND ANGLES OF 120° P –ORBITALS ORBITAL OVERLAP NEW ORBITAL The implications of these effects are: higher melting and boiling points compared to analogous alkanes lower boiling points than analogous alcohols more soluble than alkanes but less soluble than alcohols in aqueous media

Difference ALDEHYDES (RCHO) - at least one H attached to the carbonyl group thus the aldehydic group (CHO) is always terminal KETONES RCOR’ (R and R’=alkyl or aryl ) - two carbons attached to the carbonyl group C = O H CH 3 C = O H H CH 3 C = O C2H5C2H5 CH 3 Structural differences between aldehydes and ketones Aldehydes and ketones contains the same functional group, the carbonyl group (> C = O).

5 Drawing aldehydes and ketones Molecular Formula C 3 H 6 O Structural Formula C 2 H 5 CHOCH 3 COCH 3 Bond line formula C = O H C2H5C2H5 CH 3 O

NOMENCLATURE Of CARBONYL COMPOUNDS IUPAC Nomenclature of Aldehydes: Find the longest continuous carbon chain contains the CHO group to get the name of the parent hydrocarbon, the ending e is then replaced by the suffix –al. IUPAC : Methanal Ethanal Propanal Butanal Common: Formaldehyde Acetaldehyde Propionaldehyde Butyraldehyde The CHO group is assigned the number 1 position and takes precedence over other functional groups that may the present such as –OH, C=C, OR, C=O, for example:

7 Aromatic aldehydes are usually designated as derivatives of the simplest aromatic aldehyde, Benzaldehyde. IUPAC: Benzaldehyde 4-Nitrobenzaldehyde 2-Hydroxybenzaldehyde 4-Methoxybenzaldehyde Commnon: Salicylaldehyde Anisaldehyde

Nomenclature of Ketones Common names:Common names: derived by listing the alkyl substitutents attached to the carbonyl group in alphabetical order, followed by the word ketone. IUPAC names:IUPAC names: derived from the parent hydrocarbon and relpacing the ending –e by the suffix –one. The chain is numbred in such a way as give the lowest number to the C=O group. IUPAC: Propanone Phenyl ethanone 3-Buten-2-one Diphenylmethanone Common: Dimethyl ketone Methyl phenyl ketone Methyl vinyl ketone Diphenyl ketone Acetone Acetophenone Benzophenone IUPAC: Cyclopentylpropanone 3-Ethyl-2-hydroxycyclohexanone 5-Oxohexanal

PHYSICAL PROPERTIES OF KETONES AND ALDEHYDE Because the polarity of the carbonyl group, aldehydes and ketones are polar compounds. Dipole-dipole attractions,Dipole-dipole attractions, although important, are not as strong as interactions due to hydrogen bonding. As a result, the boiling points of aldehydes and ketones are higher than those of non polar alkanes, but lower than those of alcohols. The lower aldehydes and ketones are more soluble than alkanes but less soluble than alcohols in aqueous media

Preparation of aldehydes and ketones 1- Oxidation of alcohols 2- Ozonolysis of alkenes

3- Hydration of alkynes 4- Friedel Crafts acylation N.B: -COR group is m-director

Typical aldehydes and ketones ReactionsTypical aldehydes and ketones Reactions Reduction (formation of alcohols) Nucleophilic addition reactions: 1-Addition of HCN 2- Addition of acetylide anion 3-Addtion of alcohols 4-Addition of ammonia and ammonia derivatives 5- Oxidation reactions a)By K 2 Cr 2 O 7 or KMnO 4 b)By Iodoform reaction 12

REACTIONS OF ALDEHYDES AND KETONES 1- Reduction : formation of alcohols

2- By nucleophilic addition of Grignard reagent to aldehydes and ketones (formation of alcohols) Addition of RMgX to formaldehyde gives 1 ◦ alc. Addition of RMgX to any other aldehyde gives 2 ◦ alc. Addition of RMgX to ketones gives 3 ◦ alc.

3- Addition of Hydrogen Cyanide: Formation of cynohydrins 4- Addition of alkynide ions:

5- Addition of alcohols:

6- Addition of Ammonia and Ammonia Derivatives

3- Oxidation reactions a)By KMnO 4 or K 2 Cr 2 O 7 : Only aldehydes can be oxidized ketones resist oxidation Iodoform reaction: b) Iodoform reaction: This reaction gives positive result with any aldehyde or ketone has a methyl ketone group (CH 3 CO), therefore acetaldehyde is the only aldehyde gives positive iodoform test. 18