Question

1. Examine the IR spectrum of cis-norbornene-5,6-endo-dicarboxylic anhydride, (Fig.48.8, pp. 630): what do the signals at 1750 cm-1 and 1838 cm-1 indicate?

TMS 40 20 PPM 180 60 140 60 140 12010080 160 FIG. 48.8 The IR spectrum of cis-norbornene- 5,6-endo-dicarboxylic anhydride. Microns (um) 5.0 6.0 8 10 15 20 2.5 3.0 3.5 4.0 1838 cm 1759 cm-1 4000 3500 3000 2500 2000 1500 1000 500 Wavenumber (cm-1)

2. Explain the following questions regarding the possible contamination of the final isolated product with dicyclopentadiene (the cyclopentadiene dimer).

a. Since “cracked” cyclopentadiene can spontaneously dimerize back to dicyclopentadiene, could the dimer be formed as an unwanted “by-product” during the experiment?

b. How does the experimental procedure minimize contamination of the final isolated (desired) product with this (undesired) “by-product”?

Answer 1

Reaction This product can be obtained by Diels- Alder reaction. at low temp monomer of cyclopentadiene dimer heat unwanted product momomer 1) anhydride normal peaks (1760 and 1810 cm-1) there are two peaks for anhydrides at the above freq our peaks are at 1759 cm-1 and one at 1838 cm-1 (cyclic anhydride 5 membered ring again increases freq upto 30 cm-1) so , the peak at 1838 cm-1 electronegetive oxygen atom (inductive effect) between two carbonyl group increases the req, while resonanse lowers the freq 2) peak at 1100 cm-1 C-O 3) PEAKAT 1600 CM-1 alkene 4) 2850 CM-1 -3000 CM-1 ALKANE STRETCH 5) 3150 CM-1 ALKNE STRETCH 2) While cracking the dimer it will give us monomer which then reacts with maleic anhydride to give Diels-Alder product, it does not give any unwanted product at higher temperature. if cracked monomer reacted at low temp. or it does notreacted immediately with maleic anhydride then unwanted product will be obtained. 3) breaking the dimer at high temperature and it is to be reacted immediately can isolate the pure prodict