ir - isomers with the same functional groups? 4. Are the...

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EXPERIMENT: I NFRARED S PECTROSCOPY Name _______________________________________ Instructor ____________________________________ Chem ____________ Section/Color ______________ Date ________________________________________ Laboratory Questions These questions are to be completed and turned in at the beginning of the pre-lab period. PRE-LAB QUESTIONS IMPORTANT -- Reading Assignment: McMurry, Sections 12.5 - 12.9 1. What is the meaning of the abbreviation, ATR? 2. In a normal FTIR sample holder, the infrared beam passes entirely through a layer or solution of the sample. Increasing the thickness of the layer or the solution will increase the amount of infrared energy absorbed by the sample. Why does increasing the thickness of a sample from 1 mm to 3 mm on an ATR crystal not increase the amount of energy absorbed? (See lab manual techniques section) 3. What region of an IR spectrum (give a range in wavenumbers) is most useful for distinguishing between
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Unformatted text preview: isomers with the same functional groups? 4. Are the characteristic vibrations for functional groups such as carbonyl groups (aldehydes, ketones, etc.) and alcohols (RO-H) stretching vibrations or bending vibrations? Attenuated Total Reectance Light reected via Total Internal Reection (see Wikipedia for more information on this) enters less than 1 m into the sample before reecting back. The ngerprint region, with a range from 400-1400 wavenumbers. If you gave 1000-1400, that's ne and you get credit, but it's not correct. I know, the book is wrong, but for your information and future reference, it's the above range. Stretching Vibrations. The bending vibrations occur toward the ngerprint region because bending bonds requires less energy than stretching them (as we learned in the Molecular Modeling lab), because the lower wavenumbers coorespond to lower energy/frequency....
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