>> Lab Name (( Infrared Spectroscopy )) << 6. (2 pts.) Draw the structure of you

Question

>> Lab Name (( Infrared Spectroscopy )) <<

6. (2 pts.) Draw the structure of your SOLID unknown either as a Lewis structure or line-angle structure, be sure to include all non-bonding electrons and IDENTIFY ALL FUNCTIONAL GROUPS (ignore alkyl groups) 7. (4 pts.) Below is the IR spectrum of a solid sample that was taken by a student. Give Two possible causes for the weak signals observed. 100 T 90 80 70 60 50 transmission 40 30 20 4000 500 2000 3000 1500 1000 wavenumber, cm 8. (2 pts.) A student ran an IR spectrum of a liquid shown in A below, that had a strange feature indicating >100% transmission. The student realized that they had forgotten an important step, and after re-running the spectrum with the important step obtained spectrum B. What do you think the important step was that the student forgot first time?

Explanation / Answer

7. Weak signal observed in the IR spectrum for the given compound is due to lower concentration of compound present in the nujol. Secondly, the light frequency used may not be suffiicient to excite the bonds.

8.As the bond strength of sp3 < sp2 < sp C-H bond increases, due to the higher s-character, the bond energy also increases. Thus greater frequency is needed to excite the bonds in the same order and we see greater frequency shift from sp3 C-H to sp C-H stretch.

9. In the first spectrum, the broad peak between 2500-3200 cm-1 is due to O-H stretch of carboxylic acid. The peak at 1699 cm-1 is for the C=O stretch. the compound is thus, hydrocinnemic acid.

In the second spectrum, the peaks between 3000-3100 cm-1 and 1500-1610 cm-1 are due to sp2 =C-H and C=C stretch of aromatic ring. The compound is cumene.

10. In the given dehydration reaction, the starting material an alcohol would show a strong broad peak at around 3350 cm-1 for the O-H stretch. This peak disappears in the product alkene formed. Also new medium intensity peaks between 3000-3100 cm-1 and 1620-1680 cm-1 due to sp2 =C-H stretch would appear in the product formed.

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