Question

The decreasing order of priority of the following functional group is:
$1.ROH$
$2.RC \equiv CR$
$3.ROR$
$4.RN{H_2}$
A. $4 > 1 > 2 > 3$
B. $4 > 1 > 3 > 2$
C. $1 > 4 > 3 > 2$
D. $2 > 3 > 4 > 1$

Answer 1

Hint: The priority of an organic compound in chemistry can be determined by the oxidation number of the central carbon atom, greater the oxidation state of central carbon higher is its place in priority. For example, carboxylic acid has the highest priority.

Complete step by step answer:
In IUPAC nomenclature organic compounds are differentiated in different functional groups attached to the compound, different classes of compound therefore have different chemical and physical properties. If a compound contains two different functional groups then higher priority functional is considered to name the organic compound and the other functional group is considered as substitute.
Now, the priority order of the functional group is determined by the oxidation state of the central carbon atom, higher the oxidation state higher is its priority in the series of functional groups.
Now, by considering oxidation states of all functional group, we get below order of priority in decreasing order:
1. Carboxylic acid: $RCOOH${highest priority}
2. Derivatives of carboxylic acid:
${(RCO)_2}O > RCOOR > RCOX > RCON{H_2} > RC \equiv N$
(anhydride) (esters) (acid halide) (amides) (nitriles)
3. Oxygen and nitrogen containing group
$RCHO > RCOR > ROH > RN{H_2} > ROR$
(aldehydes) (ketone) (alcohol) (amines) (ester)
4. Alkenes and alkynes:
$RCH = C{H_2} > RC \equiv CH$
(alkenes) (alkynes)
5. Least priority:
$R - > RO - > X - $
(alkyl) (alkoxy) (halide)
From the above order of priority we can say that alcohol has the highest priority, after that amines, then ether and then alkynes has the least priority.
So decreasing order of priority from the question is;
‘C. $1 > 4 > 3 > 2$’.
Note: This is a trick you can use to find priority faster. Calculate the molecular mass of all the compounds, and arrange them in order of their molecular mass, except some exceptions this order will be exactly the same as the priority order of these compounds.