Organic - Aldehydes and Ketones Flashcards
What functional group is present in aldehydes and ketones?
The carbonyl group, which consists of a carbon-oxygen double bond C=O.
What is the general formula for aldehydes?
In aldehydes, the carbon bonded to the oxygen (the carbonyl carbon) has at least one hydrogen atom bonded to it, so the general formula is: RHC=O.
What is the general formula for ketones?
In ketones, the carbon bonded to the oxygen (the carbonyl carbon) has two organic groups, which can be represented by R and R’, so the general is: R’RC=O.
What can the R groups in both aldehydes and ketones be?
alkyl (based on a saturated hydrocarbon group) or aryl (based on an aromatic system)
What are the physical properties of carbonyl compounds?
The carbonyl group is strongly polar, so there are permanent dipole-dipole forces between the molecules. These forces mean that boiling points are higher than those of alkanes of comparable relative molecular mass but not as high as those of alcohols, where hydrogen bonding can occur between the molecules.
What is the solubility of aldehydes and ketones in water?
Shorter chain aldehydes and ketones mix completely with water because hydrogen bonds form between the oxygen of the carbonyl compound and water. As the length of the carbon chain increases, carbonyl compounds become less soluble in water.
What is the reactivity of carbonyl compounds?
Almost all reactions of carbonyl compounds involve the C=O bond, despite it being strong.
This is because the big difference in electronegativity between carbon and oxygen makes the C=O strongly polar, so nucleophilic reagents can attack the carbon (partially positive charge). Also, since they contain a double bond, carbonyl compounds are unsaturated and addition reactions are possible.
What is the most typical reaction of the carbonyl group?
nucleophilic addition reaction, but they also undergo redox reactions
What is a good example of a nucleophilic addition reaction?
Sodium/potassium cyanide is used as a source of cyanide ions followed by the addition of dilute hydrochloric acid. The products are called hydroxynitriles, which are useful in synthesis because both the -OH and -CN groups are reactive and can be converted into other functional groups.
Why is the addition of hydrogen cyanide an important reaction?
This reaction is important in organic synthesis because it increases the length of the carbon chain by one carbon. The products are called hydroxynitriles.
What does the reaction with the addition of hydrogen cyanide produce?
This reaction will produce a racemic mixture of two optical isomers (enantiomers) when carried out with an aldehyde or an unsymmetrical ketone, because the :CN- ion may attack from above or below the flat C=O group.
Can aldehydes be oxidised?
Aldehydes can be oxidised to carboxylic acids. [O] is used to represent the oxidising agent. One oxidising agent commonly used is acidified (with dilute sulphuric acid) potassium dichromate (VI), K2Cr2O7/H+.
Can ketones be oxidised?
Ketones cannot be oxidised easily to carboxylic acids because, unlike aldehydes, a C-C bond must be broken. Stronger oxidising agents break the hydrocarbon chain of the ketone molecule resulting in a shorter chain molecule, carbon dioxide, and water.
What is the basis of the two tests that distinguish between aldehydes and ketones?
Weak oxidising agents can oxidise aldehydes but not ketones.
What is Fehling’s test?
Fehling’s solution is made from a mixture of two solutions - Fehling’s A which contains the Cu 2+ ion and is therefore coloured blue, and Fehling’s B which contains an alkali and a complexing agent.
