Which alcohol can NOT be prepared by reduction of carbonyl compounds? a) Methyl alcohol b) Ethyl alcohol c) iso-propyl alcohol d) tert-butyl alcohol
Solution
Tertiary alcohols cannot be prepared by oxidation of carbonyl compounds.In structure of aldehyde is R-CHO, the terminal carbon is attached to oxygen with a double bond (which is known as carbonyl group). It is clear from the structure that carbonyl carbon is attached to one alkyl group and hence it is primary in nature. If we reduced it with the help of any reducing agent, then 2 hydrogen atom will add on >C=O group, one on C and other at O.
As no alkyl group is introduced on the carbonyl carbon hence it will remain primary only.
R-CHO + NaBH4 --------> R-CH2-OH
In the case of ketones, carbonyl carbon is secondary, on reducing > C=O, we get secondary alcohol only as no alkyl group has been introduced on the carbon.
R-CO-R + NaBH4 ---------> R-CH(OH)- R
If we talk about carboxylic acid then it is first reduced to aldehyde and then completely reduced to alcohol in presence strong reducing agent such as LiAlH4.
Here again we get primary alcohols.
Please note that carbonyl carbon is always primary or secondary, it can't be tertiary (as carbon cannot have a valency equal to 5).
So,Tertiary alcohols cannot be prepared by oxidation of carbonyl compounds.
hence option d is correct
Tertiary alcohols cannot be prepared by oxidation of carbonyl compounds.In structure of aldehyde is R-CHO, the terminal carbon is attached to oxygen with a double bond (which is known as carbonyl group). It is clear from the structure that carbonyl carbon is attached to one alkyl group and hence it is primary in nature. If we reduced it with the help of any reducing agent, then 2 hydrogen atom will add on >C=O group, one on C and other at O.
As no alkyl group is introduced on the carbonyl carbon hence it will remain primary only.
R-CHO + NaBH4 --------> R-CH2-OH
In the case of ketones, carbonyl carbon is secondary, on reducing > C=O, we get secondary alcohol only as no alkyl group has been introduced on the carbon.
R-CO-R + NaBH4 ---------> R-CH(OH)- R
If we talk about carboxylic acid then it is first reduced to aldehyde and then completely reduced to alcohol in presence strong reducing agent such as LiAlH4.
Here again we get primary alcohols.
Please note that carbonyl carbon is always primary or secondary, it can't be tertiary (as carbon cannot have a valency equal to 5).
So,Tertiary alcohols cannot be prepared by oxidation of carbonyl compounds.
hence option d is correct