Aldehydes, Ketones and Optical Isomerisms Flashcards
What is the functional group of carboxylic acids?
COOH
What is the functional group of Adlehydes?
R-CHO
What is the functional group of Ketones?
R-CRO
What is the product of reducing Aldehydes, and which mechanism does this use?
Primary alcohol, via nucleophilic addition
What is the product of reducing Ketones, and which mechanism does this use?
Secondary alcohols, via nucleophilic addition
What is a nucleophile?
An electron paur donor
State the reagents and conditions for the reduction of aldehydes and ketones
Reagent- NaBH4
Conditions- aqueous
What is the role of :H- ions in reduction of aldehydes and ketones?
What can this be simplified to in a balanced equation?
Nucleophile
[H] in balanced equation
What is the product of nucleophilic addition of aldehydes and ketones with KCN and HCl?
Hydroxynitriles
What are the reagents for converting aldehydes/ketones into hydroxynitriles via nucleophilic addition?
KCN and dilute HCl
In the production of hydroxynitriles via nucleophilic addition, what acts as the nucleophile?
:-CN
Why can HCN not be used in the production of hydroxynitriles via nucleophilic addition?
It is a toxic/ corrosive gas that can easily escape into the laboratory.
Whereas KCN is an ionic solid that can be readily dissolved to form a solution
What happens when Aldehydes and unsymmetrical ketones undergo nucleophilic addition with KCN and HCl?
A reacemic mixture of two enantiomers (hydroxynitriles) are formed
What are optical isomers?
Non-superimposible mirror images, also known as enantiomers
What is a racemic mixture?
A mixture of equal amounts of the two enantiomers of a compound
How does the shape of an aldehyde or unsymmetrical ketone lead to a racemic mixtire?
The carbonyl carbon has a planar shape, so the nucleophile (CN) can attack the carbon equally from above and below. This gives a racemic mixture that will not rotate plane polarised light
What must a compound have to exhibit optical isomerism?
A chiral (asymmetric) carbon that is bonded to four different groups
Why do pairs of enantiomers have the same chemical properties?
Because they have the same functional groups
How do optical isomers act in polarised light?
Optical isomers rotate plane polarised light by equal amounts in opposite directions
How do tou draw optical isomers?
Drawy the structure in a tetrahedral arrangement.
Label the chiral carbon with a *
Draw its mirror image
Why do racemic mixtures not rotate plane polarised light?
Because they have an equal ratio of each optical isomer, so rotations cancel out
How can a racemic mixtire of enantiomers be formed in a lab?
Via electrophylic addition with but-2-ene and hydrogen bromide
During the formation of enantiomers with electrophylic addition, why is it possible that a racemic mixture is formed?
During the intermediate stage, a trigonal planar carbocation is formed
Bromide has equal chances of attacking the carbon from both above and below
Equal amounts of each optical isomer is formed, producing a racemic mixture
