Chapter 26- Aldehydes and Ketones Flashcards
What are aldehydes?
Organic compounds with the -CHO functional group containing a carbonyl group C=O at the end of the molecule
How are aldehydes produced?
Produced from initial oxidation and distillation of primary alcohols
How are aldehydes oxidised?
Aldehydes are readily oxidised in the presence of acidified potassium dichromate to produce a carboxylic acid
What are two chemical tests to distinguish between aldehydes and ketones?
Tollen’s test: produces a silver mirror
Fehling’s test: goes from blue solution to red precipitate
Ketones don’t react with either of these reagents
What are ketones?
An organic molecule with the functional group C=O in the middle of the molecule
How are ketones produced?
Produced from oxidation of secondary alcohols with acidified potassium dichromate
How are ketones oxidised?
Cannot be oxidised further
What is a carbonyl group?
A functional group with a C=O double bond
What happens when aldehydes and ketones are reduced?
Aldehydes produce primary alcohols when reduced
Ketones produce secondary alcohols when reduced
What reducing agent is used to reduce aldehydes and ketones?
Sodium borohydride NaBH4 is used as a reducing agent in aqueous solution.
What is the nucleophile used when reducing aldehydes and ketones?
:H- ion is the nucleophile, provided by NaBH4 in aqueous solution.
What is a necessary condition for the reduction of aldehydes and ketones?
Aqueous conditions as an H+ ion from the water molecule is needed
What is a nucleophile?
An electron pair donor
How are hydroxy-nitriles produced and what is this process an example of?
Nucleophilic addition reactions with a -:CN nucleophile, followed by reaction with a dilute acid. This is a form of synthesis as it increases the length of the carbon chain by one.
What is the nucleophile used when producing hydroxy-nitriles?
-:CN nucleophile, provided by KCN most often
What is the reaction mechanism for producing a hydroxy-nitrile from an aldehyde or ketone?
Lone pair from -:CN nucleophile goes to δ+ C and one pair of electrons from C=O goes to O making it negative. Lone pair on O now goes to H+ ion from dilute acid to form OH group
How are enantiomers produced from the nucleophilic addition from -:CN nucleophiles?
The -:CN nucleophile can attack the C nucleus in the planar carbonyl from above or below and the C atom attacked is often a chiral centre, producing two enantiomers
How do you name hydroxy-nitriles?
C bonded to N is carbon atom one and is part of the carbon chain
What are the dangers of KCN?
Dangerous if ingested or inhaled
Reacts with moisture to produce HCN, a toxic gas
Why is KCN used as the reagent instead of HCN for production of hydroxy-nitriles?
HCN is hard to store as a gas, is toxic and reacts to form dangerous byproducts
