Question

Find the bond length of O \(-\) H in methanol

• A. 96 pm
• B. 141 pm
• C. 136 pm
• D. 145 pm
• E. 86 pm

Hint:

It's highly beneficial to remember rough approximations for common bonds to quickly eliminate wrong options:
\(\text{O-H} \approx 96 \text{ pm}\)
\(\text{C-H} \approx 109 \text{ pm}\)
\(\text{C-O} \approx 142 \text{ pm}\)
\(\text{C-C} \approx 154 \text{ pm}\)

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Bond lengths are characteristic physical properties of molecules determined experimentally (e.g., via spectroscopy or X-ray crystallography). This question tests direct factual recall of structural parameters for a fundamental organic molecule, methanol (\(\text{CH}_3\text{OH}\)).
Step 2: Key Formula or Approach:
There is no calculation required here; the approach relies entirely on recalling standard textbook data regarding the molecular geometry of alcohols.
Step 3: Detailed Explanation:
In a molecule of methanol (\(\text{CH}_3\text{OH}\)):
- The oxygen atom is \(sp^3\) hybridized.
- It forms a single bond with carbon (\(\text{C}-\text{O}\)) and a single bond with hydrogen (\(\text{O}-\text{H}\)).
- The standard experimentally determined bond length for the carbon-oxygen (\(\text{C}-\text{O}\)) bond in methanol is approximately 142 pm.
- The standard experimentally determined bond length for the highly polar oxygen-hydrogen (\(\text{O}-\text{H}\)) bond is significantly shorter, approximately 96 pm.
Looking at the options provided, 96 pm exactly matches the standard value for the \(\text{O}-\text{H}\) bond. Values like 141 pm or 145 pm would be much closer to the \(\text{C}-\text{O}\) bond length or a \(\text{C}-\text{C}\) bond length respectively.
Step 4: Final Answer:
The \(\text{O}-\text{H}\) bond length in methanol is 96 pm.