PowerPoint to accompany hapter 25 Aldehydes, Ketones and arbohydrates arbonyl ompounds ontain = double bond. Include many classes of compounds: aldehydes, ketones, carboxylic acids, esters, amides. ' ' N '' ' Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Education
Aldehydes haracterised by the functional group. ontains a carbonyl group Both carbon and oxygen are sp 2 hybridised. Figure 25.1 Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Aldehyde Nomenclature Name the longest chain containing the carbonyl group and replace ane with al. Must, by definition, occur at one of the ends of a molecule. emember that aldehyde group takes priority over both methyl and hydroxyl groups. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Education
Ketones Name the longest chain containing the carbonyl group and replace ane with one. arbonyl group is bonded to alkyl groups on either side. progesterone camphor testosterone Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Ketone Nomenclature Longest chain containing the carbonyl group. eplace ane with one. onstitutional isomers occur for 5 or greater. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Education
Preparation of Aldehydes and Ketones xidation of alcohols using a range of reagents Most are chromium(vi) compounds (r 3 ). Again, different types of alcohols yield different products Primary alcohols can lead to aldehydes and carboxylic acids. Secondary alcohols lead to ketones. Tertiary alcohols do not oxidise. Figure 25.2 Preparation of Aldehydes and Ketones Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Education
Preparation of Aldehydes and Ketones Using pyridinium chlorochromate (P) Preparation of Aldehydes and Ketones Secondary alcohols can be oxidised by P, Jones eagent or K 2 r 2 7 to yield the corresponding ketone. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Education
ozonolysis Aldehydes and ketones can also be prepared in good yields by the reaction of alkenes with ozone, followed by a mild reduction using dimethylsulfide. This reaction is called ozonolysis eactions Aldehydes and Ketones In general Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Education
eduction eactions Aldehydes and ketones can be reduced to give alcohols atalytic hydrogenation is one way Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson ydrides: eduction eactions Figure 25.5 Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Education
Tautomerism in Aldehydes and Ketones Aldehydes and ketones bearing -hydrogen are able to undergo tautomerism to form enols (i.e. compounds bearing an alkene and an alcohol). Enols are constitutional isomers of their respective keto form (i.e. aldehyde or ketone). Tautomerism is the process by which two isomers are interconverted by a formal movement of an atom or group bearing in mind valency rules. ence, an enol and its keto form are tautomers of the same structure. Aldehydes and ketones are in equilibrium with their enol forms and this equilibrium is acid catalysed. The process involves two separate proton transfers: The extent of tautomerisation is dependent on the aldehyde or ketone: Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Education
alogenation of Aldehydes and Ketones Aldehydes and ketones undergo a substitution reaction at the α- carbon in the presence of halogen in good yield. This reaction is regiospecific in that only the α-hydrogen is substituted under these conditions. The rate determining step in this reaction is the conversion of the ketone to its enol isomer, e.g. Brown, LeMay, Bursten, Murphy, Langford, Sagatys: hemistry 2e 2010 Pearson Education