Question

Sodium Borohydride Reduction of Benzoin Pre-Lab Worksheet

(1) Why is it important to use 100% ethanol for this reaction? 5, ethanol (absolute ethanol) rather than 95% of benzoin? ow would you expect the IR spectrum of the reduced product to differ from that 7. (2) How would you expect the 1H rom that of benzNMR spectrum of the reduced product to differ 8. (2) How many peaks do you expect in the 13C NMR spectrum of the product? Suppose you reduced the ketone below with sodium borohydride. Draw the ctures of the two isomeric products, and state the relationship between them. 9. (3) stru 7 NaBH4 EtOH H3C camphor

Answer 1

5.Since sodium borohydride is highly hygroscopic and reactive towards active hydrogen containing molecules such as water and acids. So any water content present in alcohol may lead to hazard.

6. Reduced product no longer possess keto functional group in benzoin (carbonyl group), hence there will be absent of strong peak in the region 1705-1725 cm-1, which is is present in starting compound benzoin.

7. Due to the formation of symmetrical dihydroxy product, 1H NMR of product shows simple splitting pattern compared to starting material. Product shows only 3 signals, one multiplet, and two singlets.

8. Again due to symmetry we can expect 5 13C NMR signals only.

9. Answer is in below image, the products are diastereomers. EtOH and H₃O⁺ both will same as they supply H⁺.

CH HAC CH CH 3 н.с 3 3 3 3 1 NaBH4 он CH CH CH 3 3 3 camphor (endo) (exo) borneol isoborneol

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