im having hard time with questions 3-6 this is a prelap concerning 5 kinds of pl

Question

im having hard time with questions 3-6
this is a prelap concerning 5 kinds of plastic
PETE
HDPE
PVC
PP
PS

that the text index shows PVC uhder t 3. Of the five chemical types of recyclable plastics on the previous page, which should give the simplest infrared spectrum, and why? 4. What is the "fingerprint" region of the infrared spectrum and why is it called this? 5. If an infrared spectrum displayed a deep. broad absorbance at about 3400 cm', what groups could this be attributed to? 6. If a sample contained an aromatic ring, what evidence would you expect to see in its spectrum?

Explanation / Answer

3) IR spectrum is recorded as a plot of transmittance versus frequency in IR range. Each functional group absorb light at a particular wavelength and hence we see deep in transmittance at that frequency. Moreover, all interactions occur due to surrounding environment will affect the spectrum.

According to that whichever plastic have less number of functional groups will give simple IR spectra so the answer is HDPE.

4) In IR spectrum region starting from 400 cm-1 to the 1000 cm-1 contains very complicated absorptions due to all bending vibrations within the molecule. This particular region is called as fingerprint region because every molecule has a unique absorption spectrum in this region similar to the unique fingerprint of the human.

5) The broad peak in 3200 to 3600 cm-1 region is mostly due to the hydrogen bonded O-H stretching, also secondary amine N-H will give the broad peak in this region but its weak compare to O-H. primary amine will give two peaks in this region.

6) Aromatic ring contains C=C and C-H modes absorb at 1400-1600 cm-1 and 3000-3100 cm-1 respectively in its IR spectrum.

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