question_answer

Which of the following is the correct order of priority of group in D-glyceraldehyde?

A) \[OH(1),CHO(2),\text{ }C{{H}_{2}}OH(3)\] and \[H(4)\]

B) \[OH(1),\,\,C{{H}_{2}}\,\,OH(2),\,\,CHO(3)\] and \[H(4)\]

C) \[C{{H}_{2}}OH(1),\,\,CHO(2),\,\,OH(3)\] and \[H(4)\]

D) \[CHO(1),\,\,OH(2),\,\,C{{H}_{2}}OH(3)\] and \[H(4)\]

Correct Answer: A

Solution :

[a]

The structure of D-glyceraldehyde is as :

The priority of groups is decided by the following rules:

(i) Atom having higher atomic number gets higher priority.

(ii) If the priority cannot be decided by rule 1 then the next atoms are considered for priority order.

(iii) Where there is a \[=\] bond or \[\equiv \] bond, both atoms are considered to be duplicated or triplicated.

\[(\overset{H}{\mathop{\overset{|}{\mathop{C}}\,}}\,=O\] has higher priority than \[C{{H}_{2}}OH).\]

Hence, the correct order of priority of group in D-glyceraldehyde is as follows:

\[OH(1).\,\,CHO(2),\,\,C{{H}_{2}}OH(3)\]and \[H(4)\]