Question

4. IR SPECTROSCOPY Run the IR spectrum of your product using the Nujol mull technique; attach the spectrum to your report. Cinnamic acid contains a carboxyl group (-CO,H) in which the carbon-oxygen double bond is "conjugated" with the carbon-carbon double bond (C=C-C=O). The C=O stretching absorption appears at about 1685 cm in cinnamic acid. (a) What is the frequency of the CO stretching absorption in your product? (b) What effect does conjugation have on the frequency of the CEO stretching absorption? 5. ANSWER THE FOLLOWING QUESTIONS The reaction of alkenes with osmium tetroxide (Os) results in the formation of vicinal diols. c=¢ Oso HO PH MezCOOH The mode of addition in this case is "syn," that is the two hydroxyl groups become attached to the same face of the double bond. Consider the reaction of trans-cinnamic acid with osmium tetroxide to give PhCHOH-CHOH-CO, H (2,3-dihydroxy-3- phenylpropanoic acid. Complete the Newman projection below to show clearly the stereochemistry of the product produced in this reaction. ÇOH ph What is the correct stereochemical designation of this compound, is it an erythro or is it a threo compound?

Answer 1

ha) The wore number of c-o stretching in the is 17/24 cm - etching in the product 1725 cm- The frequency of c- O stretching in the produce VE CŪ= 3x10 cm/s x17/2.46M-'35. 137x10 6) Nos conjuncted to tones have cao stretch at conjugated Calpha beta naturated) ketones have c=0 stretch at 1665-1685 cm-1 Due to conjugation, the pi electrons of c= o group are de localised co bond order is less than a Hence conjugated cao bond is creaker than unconjugated cao bond. Hence, absorption accurs at lower frequence.