IR questions. 1. when only information you have is an IR spectrum, why is it nec

Question

IR questions.

1. when only information you have is an IR spectrum, why is it necessary to have a list of compounds to choose from?

2. the absorption for carbon dioxide appears around 2300 cm-1. spectra often contain this band. Do any the below diagram spectra show this absorption? why won't it always be taken out by subtracting the background spectrum?

Transmittance 8 3309.59 3082 808 - 8 > 2923.08 2857.65 8 1717.501701.001670.221646.85 1559.411540. 961 533:981521.99-15073F 1457.01 1421.19 1340.16 312.81 1230.06 1110.36 1023.34 8 990 84 915.08

Explanation / Answer

Question 1

you can use this technique for identifying the functional groups in organic compounds and it will not give any structural environment of the molecule. Hence you need to have a list of compounds to match. From the functional groups of the compound we can identify the exact compound using IR spectrum.

Question 2

The given spectra does not contain any CO2 band. It may substracted from background spectrum.  Because if you take background spectrum you will get a peak for CO2 which is present in air. If you take IR for sample that also will contains CO2 band. Hence If you substract your sample specturm with background spectrum you will not get any CO2 band in resulting spectrum. Because of this reason IR always be taken out by subtracting the background spectrum.

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