What IR spectrum change indicates the conversion of benzophenone to diphenylmethanol?

The conversion of benzophenone to diphenylmethanol involves the reduction of the carbonyl group (C=O) present in benzophenone. In the IR spectrum, the presence of a carbonyl group typically shows a strong absorption peak in the region of 1700 cm⁻¹. When benzophenone is converted to diphenylmethanol, the carbonyl group is reduced to a hydroxyl group (−OH), leading to the disappearance of the peak associated with the carbonyl stretch.

Thus, the correct indication of this transformation in the IR spectrum is the disappearance of the peak around 1700 cm⁻¹, signifying the loss of the carbonyl functionality that was present in benzophenone. Instead, one would expect to see peaks associated with the alcohol functionality, typically around 3200-3600 cm⁻¹ for the OH stretching, but the focus here is on the significant change pertaining to the carbonyl stretch. This disappearance is crucial in identifying and confirming that the reduction has taken place successfully.