1 / 12

Lecture 13

Lecture 13. IR: Theory & Lab Guide Problems (IR & IR with NMR) This week in lab: Ch 7: TLC, PreLab Due Quiz 4 Spec Unknown Progress Check Due Next week in lab: Ch 8: Column Chromatography, PreLab Due Quiz 5. IR Spectroscopy.

arawn
Download Presentation

Lecture 13

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lecture 13 IR: Theory & Lab Guide Problems (IR & IR with NMR) This week in lab: • Ch 7: TLC, PreLab Due • Quiz 4 • Spec Unknown Progress Check Due Next week in lab: • Ch 8: Column Chromatography, PreLab Due • Quiz 5

  2. IR Spectroscopy Main Use: To detect the presence or absence of a functional group (specific bonds) in a molecule How It Works: Bonds vibrate freely at specific wavelengths (wavenumbers) Want to cause the bonds to increase the magnitude of this vibrational frequency Subject compound to IR radiation, 4000-625 cm-1 cm-1 is the unit for wavenumber (n) n is directly proportional to energy (unlike wavelength) 4. Bonds absorb energy equal to their natural vibrational energy - it is quantized. This absorption of energy causes a change in dipole moment for the bond. 5. Upon absorption, bonds stretch and/or bend; the IR measures this absorption.

  3. IR spectrum of hexanoic acid

  4. Correlation Chart Specific bonds absorb specific IR radiation and signals will appear within certain wavenumber ranges (similar to NMR). Note: O-H stretches are broader than N-H stretches N-H Stretches: 1° Amines (RNH2) has two peaks 2° Amines (RNHR) has one peak 3° Amines (NR3) has no peaks

  5. Correlation Chart Specific bonds absorb specific IR radiation and signals will appear within certain wavenumber ranges (similar to NMR).

  6. Lab Guide Problem 11.15 A sample is known to have the molecular formula C4H10O and to be one of two constitutional isomers, either t-butyl alcohol or isopropyl methyl ether. Refer to IR spectrum (Figure 11.23) What is the structure of the unknown? 1. Look at structures of the two possibilities: 2. Determine the main differences that would be seen in IR and evaluate IR. 3. Structure:

  7. Lab Guide Problem 11.16 Indicate how the following pairs of compounds could be distinguished using characteristic IR peaks: (a) Benzaldehyde (C6H5O) and benzoic acid (C6H5COOH) 1. Consider each structure: benzaldehyde Benzoic acid 2. Determine the main differences that would be seen in IR.

  8. Lab Guide Problem 11.16 Indicate how the following pairs of compounds could be distinguished using characteristic IR peaks: (b) Cyclobutene and 2-pentyne 1. Consider each structure: cyclobutene 2-pentyne 2. Determine the main differences that would be seen in IR.

  9. Lab Guide Problem 11.44 An unknown oxygen-containing compound is suspected of being an alcohol, a ketone, or a carboxylic acid. Its IR spectrum shows a broad strong peak at 3100-3400 cm-1 and a strong, sharp peak at 1700 cm-1. What kind of compound is it? Consider what type of bonds appear in the ranges given. Refer to correlation chart. Broad peak at 3100-3400 cm-1 Strong, sharp peak at 1700 cm-1 

  10. Lab Guide Problem 11.45 A compound with molecular formula C4H8O shows no absorption in the IR region near 1700 cm-1 or 3400 cm-1. What can you deduce about its structure? Propose one possible structure. What can you deduce about its structure? Propose one possible structure. Calculate HDI. 2. Give possible structure(s):

  11. Lab Guide Problem 11.53(e) Propose a structure that is consistent with the following data: C7H8O (HDI = 4) 1H NMR: 2.43 ppm (s, 1H) 4.58 ppm (s, 2H) 7.28 ppm (m, 5H) IR: 3350 cm-1 Possible compound(s):   Solution: Double check structure. Make sure splitting patterns and ppm values make sense as well as the integration values. Be sure that the number of different atoms matches the MF!

  12. Lab Guide Problem 11.53(f) Propose a structure that is consistent with the following data: C3H6O2 (HDI = 1) 1H NMR: 1.27 ppm (t, 3H) 2.66 ppm (q, 2H) 10.95 ppm (s, 1H) IR: 1715 cm-1 3500-3000 cm-1 Possible compound(s):    Solution: Double check structure. Make sure splitting patterns and ppm values make sense as well as integration values. Also, make sure the numbers and types of atoms match the MF!

More Related