After completing the experiment, it was concluded that the Grignard reaction did not happen, and the diphenylmethanol was not formed.
This experiment was not successful mainly because no Grignard reagent or tiny amount of Grignard reagent was produced or active prior to addition of benzaldehyde. By the end of the lab, only berry-redish solution was produced without any solid, this is a physical evidence of not producing any diphenylmethanol, because diphenylmethanol is white crystal. Also, after adding bromobenzene, it was barely seen bubbling in the flask; however, there was supposed to have a lively reflux in the flash as a consequence of the exothermic reaction; hence, no Grignard reagent was expected to be produced. These physical observations are aligned with IR spectroscopy analysis. The presence of a peak at 1706.06 cm-1 indicates the presence of carbonyl group, (in this case, benzaldehyde)
Peaks at 3065.46, 2959.13, 2927.61 cm-1 were likely to be aromatic C-H stretches. To the right of the aromatic C-H stretches, it was appeared a shoulder-type peak at 2872.07 and 2732.33 cm-1, which proves the presence of aldehyde group. In the IR graph, a very weak peak at 3396.06 cm-1 can be found. It falls in the alcohol group range, but it is very weak. Considering the actual lab situation, it is more likely to be the water group. The NMR graph doesn’t support this specific lab result since it is from another sample. This specific NMR result indicates a successful experiment, a fairly complete reaction with producing diphenylmethanol. Comparing the chemical shift with the NMR correlation chart offered in Zubrick, the small peak at 10.1 ppm represents the aldehyde H. It is shifted more downfield than usual because of the effect of aromatic ring. The evidence of barely noticeable peak at 10.1 ppm indicates the completion of Grignard reaction. Multiplet in 7.2-7.4 ppm corresponds to aromatic ring H, because that range is where aromatic H falls, and it has multiplet. Since the slitting patterns is to determine the connectivity of the molecule, and the specific proton requires the presence of other protons that are attached to adjacent carbons, it can be determined that the multiplet can only be aromatic H. Another evidence is the integration under these signals tells the number of equivalent H’s are giving rise to a particular signal; by look at the structure of diphenylmethanol, it can be determined that diphenylmethanol has 10 aromatic H, which close to the integration number 12.4419. (The extra may come from the solvent, since the solvent is around 7.2 ppm.) From this knowledge of integration of signal, it is known that the singlet at 5.8638 and 1.9920 ppm represent the benzylic H and alcohol H. The chemical shift of alcohol H falls into the range provided in Zubrick, and it is known that alcohol H often times is described as a broad hump, which applies to this graph; thus, peak at 1.9920 represents the alcohol H. The peak at 5.8638 ppm represents the benzylic H. It is shifted more downfield than usual because of the effect of two aromatic rings and an alcohol group. As a result, it can be concluded that the product is diphenylmethanol and the reaction went fairly well.
Since no solid was produced, the melting point cannot the measured. In the very good case that lab was carried out successfully and diphenylmethanol was produced, the melting point should be around 69 oC; lower melting point indicates the presence of impurities.
Reflecting back, the possible cause leading unsuccessful experiment would be formed Grignard reagent reacted with water (moist air) first, causing no effective Grignard reagent left in the flask prior to addition of benzaldehyde. This needs to be improved in the future by closely monitoring lab experiment and assembling apparatus quickly.