Reactions Of Carbonyl Compounds
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What reduces carbonyl compounds and to what
Powerful reducing agent LiAlH4 to alcohols
What is sample dissolved in in reduction reaction and why
Dry ether to prevent water and moisture from entering because the LiAlH4 is easily hydrolysed and reacts violently with water
Two steps of reduction reaction
It is reduced by LiAlH4 which supplies hydride ions(nucleophile) to form a salt containing a complex aluminium ion and then addition of dilute acid to destroy excess hydride ions and release the alcohol from the complex ion
Why can’t LiAlH4 be used to reduce alkenes
Need to use H2 as there is repulsion of hydride ions by area of high electron density of the double bond
What is hydrogen cyanide and how is it formed
H-C triple bonded to N. Highly toxic gas formed by adding potassium cyanide to dilute sulfuric acid in the reaction mixture
Why must the potassium cyanide be in excess in nucleophile addition of hydrogen cyanide
To ensure there are free cyanide ions ready to start the reaction
Product of nucleophilic addition with cyanide ions and how to name
Produces hydroxynitrile, start counting carbon chain with carbon in nitrile group as highest priority and if alcohol that comes first in name eg 2-hydroxypropanenitrile
Why is the reaction with cyanide ions useful
Adds a carbon atom to the chain, useful step in synthetic routes to valuable compounds
Explain process of nucleophilic addition with hydrogen cyanide
-cyanide ion(nucleophile) uses its lone pair to form a bond with delta positive carbon of carbonyl group (as EN oxygen draws electrons away from it) which causes one of the double bonds to break heterolytically meaning oxygen has gained one electron from carbon and now has negative charge and extra lone pair -negatively charged oxygen then acts as a base and gains a proton from a hydrogen cyanide molecule/water molecule
When does nucleophilic addition with hydrogen cyanide product a chiral compound
With aldehyde and asymmetrical ketone
Why does nucleophilic addition with hydrogen cyanide produce racemic mixture if product is chiral
As the atoms around the carbon atom of carbonyl group trigonal planar, so attacking nucleophile has equal chance of attacking from above or below so produces equal proportions of enantiomers so mixture optically inactive as rotation by each enantiomer cancels out
What is also produced by nucleophilic addition with cyanide ions apart from hydroxynitrile
Cyanide ions, so are regenerated
Reagents of nucleophilic addition with cyanide ions
Excess potassium cyanide and dilute sulfuric acid
Where is lone pair on cyanide ions
On carbon atom