Question

Rank the following groups in order of decreasing priority?

a.${\mathbf{\text{-COOH,-H,-NH}}}_{\mathbf{2}}\mathbf{\text{,-OH}}$

b.${\mathbf{\text{-CH}}}_{\mathbf{2}}{\mathbf{\text{CH}}}_{\mathbf{3}}{\mathbf{\text{,-CH}}}_{\mathbf{3}}{\mathbf{\text{,-H,-CH(CH}}}_{\mathbf{3}}{\mathbf{\text{)}}}_{\mathbf{2}}$

c.${\mathbf{\text{-H,-CH}}}_{\mathbf{3}}{\mathbf{\text{,-Cl,-CH}}}_{\mathbf{2}}\mathbf{\text{Cl}}$

d.${\mathbf{\text{-CH=CH}}}_{\mathbf{2}}{\mathbf{\text{,CH}}}_{\mathbf{3}}\mathbf{\text{,C≡CH,-H}}$

Short answer

a. ${\text{-OH>-NH}}_2\text{>-COOH>-H}$

b. ${\text{-CH(CH}}_3{\text{)}}_2{\text{>-CH}}_2{\text{CH}}_3{\text{>-CH}}_3\text{>-H}$

c. ${\text{-Cl>-CH}}_2{\text{Cl>-CH}}_3\text{>-H}$

d.${\text{-C≡CH>-CH=CH}}_2{\text{>-CH}}_3\text{>-H}$

Step-by-step solution

Highest priority groups

The molecules containing atoms or ions of high molecular masses are placed at the first priority. The order of the priority of some groups is:

$\text{H<C<O<F<Cl<Br<I}$

The double bonded groups are multiplied by the same group on the place of a bond.

Explanation

a. The order of priority is shown as:

${\text{-OH>-NH}}_2\text{>-COOH>-H}$

The order of the highest priority follows as:

$\text{H<C<N<O}$

Therefore, -OH has the highest priority and H has the lowest priority.

b. The order of priority is shown as:

${\text{-CH(CH}}_3{\text{)}}_2{\text{>-CH}}_2{\text{CH}}_3{\text{>-CH}}_3\text{>-H}$

The order of the highest priority follows as:

$\text{H<C}$

Therefore, ${\text{-CH(CH}}_3{\text{)}}_2$has the highest priority (highest molecular mass) and H has the lowest priority.

c. The order of priority is shown as:

${\text{-Cl>-CH}}_2{\text{Cl>-CH}}_3\text{>-H}$

The order of the highest priority follows as:

$\text{H<C<Cl}$

Therefore, Cl has the highest priority (highest molecular mass), and H has the lowest priority.

d. The order of priority is shown as:

${\text{-C≡CH>-CH=CH}}_2{\text{>-CH}}_3\text{>-H}$

The order of the highest priority follows as:

$\text{H<C<C=C<C≡C}$

Therefore, $\text{C≡CH}$has the highest priority (the triple bond triples each carbon in the molecule) and H has the lowest priority.