Question

The correct order of increasing C- O bond length of
$ CO, CO_3^{2-} , CO_2 $ is

• A. $ CO_3^{2-} < CO_2 < CO $
• B. $ CO_2 < CO_3^{2-} < CO $
• C. $ CO < CO_3^{2-} < CO_2 $
• D. $ CO < CO_2 < CO_3^{2-} $

Answer 1

Answer: (D)

Method (1) Bond-multiplicity increases bond-length.
Thus,
(i) $C \equiv) \rightarrow$ has least bond-length.
(ii) $O = C + O \rightarrow$ next to $C = O$.
(iii)
Hence, increasing order of bond-length is $CO < CO _{2}< CO _{3}^{2-}$
Method (2)
(i) More be the value of bond-order smaller be the bond-length and more be the bond-energy.
(ii) Bond-order (BO) =
Total number of bonds associated between two atoms in all structure
T otal number of canonical forms
(a) $CO \rightarrow C \equiv O \rightarrow BO =\frac{3}{1}=3$
(b) $CO _{2} \rightarrow O = C = C \rightarrow BO =\frac{4}{2}=2$
Hence, order of bond-length $CO < CO _{2}< CO _{3}^{2-}$
Epimer is used to designate diastereomers that differ in configuration at only one chiral centre.