Question

The correct increasing order of C-H(A), C-O(B), C=O(C) and C\(\equiv\)N(D) bonds in terms of covalent bond length is :

• A. A \(<\) D \(<\) C \(<\) B
• B. A \(<\) B \(<\) C \(<\) D
• C. D \(<\) C \(<\) B \(<\) A
• D. D \(<\) C \(<\) A \(<\) B

Hint:

Bond order is the dominant factor for bonds between similar-sized atoms: Single \(>\) Double \(>\) Triple in length. However, C-H is exceptionally short because H is in the 1st shell.

Answer 1

The Correct Option is A

To determine the increasing order of bond lengths for C-H, C-O, C=O, and C≡N bonds, we need to consider the nature of these bonds:

1. \(C-H\) Bond: This is a single bond between carbon and hydrogen. Single bonds are generally longer than double or triple bonds.
2. \(C-O\) Bond: This is also a single bond between carbon and oxygen. Since oxygen is more electronegative than hydrogen, the C-O bond tends to be slightly shorter than the C-H bond. However, single bonds are typically longer than multiple bonds.
3. \(C=O\) Bond: A double bond between carbon and oxygen, which is shorter than the single C-O bond due to increased electron sharing and bond strength.
4. \(C\equiv N\) Bond: This is a triple bond between carbon and nitrogen, which is the shortest due to even greater electron sharing and bond strength. 

The bond length generally decreases as the bond order increases (single < double < triple) due to stronger attraction between the bonded atoms at higher bond orders. Therefore, the order of increasing covalent bond lengths is:

• \(C\equiv N\) (D): Shortest, due to triple bonding.
• \(C=O\) (C): Shorter, due to double bonding.
• \(C-O\) (B): Longer, due to single bonding.
• \(C-H\) (A): Longest, as it is a single bond with hydrogen.

Thus, the correct increasing order of bond lengths is: A (C-H) < D (C≡N) < C (C=O) < B (C-O). This matches with the given correct answer.