Identify the correct decreasing order of acidic strength for the indicated hydrogen atoms in the following compounds: I. II. III.

Step-by-step solution

The acidic strength of a C-H bond is directly proportional to the s-character of the carbon atom. A higher s-character stabilizes the conjugate base (carbanion) because the lone pair of electrons is held closer to the nucleus. In strained ring systems, the internal C-C bonds have smaller bond angles, which requires them to have a higher p-character. To compensate, the exocyclic C-H bonds acquire a higher s-character. The angle strain at the bridgehead carbon is highest in bicyclo[1.1.0]butane (I) because it consist