Question

In the reaction of benzil reduction with sodium borohydride, the stander melting point of meso-hydrobenzoin is 137 Celsius. However, in the lab, the meso-hydrobenzoin's melting range is 133.4-136.2 Celsius. Below is the IR of benzil and hydrobenzoin.

benzil Thu Nov 29 14:55:20 2018 (GMT-05:00 Number of sample şcanis: 32 96 Resolution; 8.000 Samplė gain: 1.0 94-Misror velo 92 986 84 1000 2500 Wavenumbers (cm-1) 4000 3500 3000 2000 1500

1）Comment on the major features in each IR spectrum that indicate that the transformation was successful.

2) Base on the lab's melting range and the IR spectrum, comment on the purity of your product.

Answer 1

The transformation was successfully completed,and clear seen when we compare both spectrum.

The IR spectrum of hydrobenzoin, absent of abs. band of ketone (Benzoin), new band of alcohol was appeared, aliphatic -C-H (sp3) stretch. vibr. about 2900 cm-1 also appeared and C-O- bands also appeared at about 1000 cm-1.

In case of benzyl The absorption band at about 3080 cm^- 1 due benzene - CH stretchiy (SP^2) , & 2000 - 1600 cm^- 1 due to combination bounds are present & about 1580, 1460 cm^- 1 due to benzene CH bending v b modes The smong abs bound obtained at about 1680 cm^- 1 due to conjugated canbonyl group og benzyl In the case of Hydro - benzoin A new absorption bond appeared at rightarrow ~ 3320 cm^- 1, & eqent same of benzene ring new bound at about 2900 cm^- 1 due to c^- H stret (sp^3) bond and about ~ 1000 cm^- 1 due to c - 0 stret bound The absorption bond for crebozl is absent at 1600 - 1700 cm^- 1, a clear evidence for the purity of Hydro benzoin But m . p is love rod about 1 degree c from literature m . p It may be due to it was not proper dried, If can be dried at 40 degree