Ir lecture-2010

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Ir lecture-2010

  1. 1. The scale UNITS: cm-1 unit is the wavenumber and is given by 1 / (wavelength in cm). ṽ = 1/ λ Infrared (IR) spectroscopy deals spectrum with the interaction between a molecule and radiation from the IR region of the electromagnetic (IR region = 4000 - 400 cm-1).
  2. 2. IR radiation causes the excitation of the vibrations of covalent bonds within that molecule ( motions between nuclei). These vibrations include the stretching and bending modes
  3. 4. How to can we type a Compound by IR? <ul><li>Draw four lines on your IR spectrum </li></ul><ul><li>3000 cm -1 </li></ul><ul><li>2500 cm -1 </li></ul><ul><li>2000 cm -1 </li></ul><ul><li>1500 cm -1 </li></ul><ul><li>Get a big picture first! </li></ul>
  4. 5. It is important the frequency of the energy absorbed by the type of bond (E= hC/  ) and the shape of the peak corresponding to that absorption A B C D E F <ul><li>broad and strong, typical of alcohols, centered around 3300cm -1, takes 80 % of the chart </li></ul><ul><li>broad and medium, typical of carboxylic acids, is not as smooth as alcohols due to other absorptions in the same region, 50% of the chart. </li></ul><ul><li>Sharp strong, typical of carbonyl group around 1700 cm -1, Usually, 98% of the chart </li></ul><ul><li>Sharp strong, typical of Ξ C-H centered around 3300 cm-1, usually 75% of chart </li></ul>E. Sharp medium, typical of C=C bond and others in the finger print region F. Sharp weak, typical of amines, and overtones
  5. 6. The IR Chart 1800-1600 C=O C=N C=N ~3300 H-EN ~2300 C Ξ C C Ξ N
  6. 7. <ul><li> </li></ul><ul><ul><li>Compound class Bond Frequency (cm-1) </li></ul></ul>U S 3000 1500 Saturated Sp3 carbon stretching Saturated Sp3 carbon Bending FINGERPRINT <ul><li>Above 3000 cm -1 [X-H (X = O, N, sp Ξ C, or sp 2 = C)] </li></ul><ul><li>3000-2500 [C-H (sp 3 C –H) stretching] </li></ul><ul><li>2500-2000 (C Ξ C, C Ξ N triple bond stretching) </li></ul><ul><li>2000-1500 [C=O, appr.1700; C=C and N=O, appr. 1600] </li></ul><ul><li>Under 1500 (fingerprint region) </li></ul>
  7. 8. Single bonds: n-hexane Alkanes C-H 2960-2850 (strong, stretching), 1470-1350 (bending) U S
  8. 9. Double bonds/hydrocarbons <ul><li> </li></ul><ul><li>Alkenes, arenes </li></ul><ul><li>=C-H </li></ul><ul><ul><li>Compound Bond Frequency (cm-1) </li></ul></ul>U S 3000 1500 Saturated Sp3 C-H stretching Saturated Sp3 carbon bending Unsaturated Sp2 C-H stretching ~ 1600 cm -1 C=C stretching
  9. 10. Double bonds /hydrocarbons Alkenes 2-hexene C=C, 1680-1640 (medium, stretching) C-H 3090-3020 (strong, stretching), 1000-675 (bending) C=C
  10. 11. Methyl benzene Aromatic Rings C=C 1600-1500 (stretching) =C-H 3100-3000 (stretching), 2000-1600 (phenyl ring substitution overtones) U S overtones Double bonds /hydrocarbons
  11. 12. Other Double bonds <ul><li>Nitro Compounds </li></ul><ul><li>N=O 1660-1500 (s, asymmetrical s </li></ul><ul><li>1390-1260 (s, symmetrical stretching) </li></ul><ul><li>C=O 1760-1670 (s, stretching) </li></ul><ul><ul><li>FAMILY A </li></ul></ul><ul><li>Aldehydes, </li></ul><ul><li>Ketones, </li></ul><ul><ul><li>FAMILY B </li></ul></ul><ul><li>Carboxylic acids, </li></ul><ul><li>Esters </li></ul><ul><li>Amides </li></ul><ul><li>Acyl halides </li></ul><ul><li>Acid Anhydrides </li></ul><ul><li>C=O 1760-1670 (s, stretching) </li></ul>
  12. 13. Acetone: Residues of acetone used during cleaning or in contamination during GC analysis will be observed with a weak peak at 1715 cm-1 Other double bonds
  13. 14. 1-HEXYNE Triple bonds /hydrocarbons Alkynes C-H 3333-3267(sharp, strong, stretching), 700-610 (bending) C Ξ C 2260-2100 (sharp, medium, stretching) Ξ C-H C Ξ C
  14. 15. Internal Alkyne C Ξ C overtones C=C
  15. 16. Triple bonds <ul><li>Alkynes </li></ul><ul><li>C-H 3333-3267(sharp, stretching), </li></ul><ul><li>700-610 (bending) </li></ul><ul><li>C Ξ C 2260-2100 (sharp, strong, stretching) </li></ul><ul><li>Nitriles </li></ul><ul><li>C Ξ N 2260-2220 (sharp, strong stretching) </li></ul><ul><ul><li>Compound Bond Frequency (cm-1) </li></ul></ul>
  16. 17. Cyano benzene C=C C Ξ N Nitriles C Ξ N 2260-2220 (sharp, strong stretching)
  17. 18. <ul><li>Alcohols, Phenols </li></ul><ul><li>O-H (H-bond formation) 3640-3160 (s & br, stret.) </li></ul><ul><li>Carboxylic acids </li></ul><ul><li>O-H (H-bond formation) 3500-2500 (b, stretching) </li></ul><ul><li>Amines </li></ul><ul><li>N-H (H-bond formation) </li></ul><ul><li>(2 peaks for primary amine, one peak for secondary amine) </li></ul><ul><li>3500-3300 (m, stretching) </li></ul>H-Electronegative atom <ul><ul><li>Compound Bond Frequency (cm-1) </li></ul></ul>
  18. 19. 1-pentanol
  19. 20. Difference between a carboxylic acid and an alcohol. Hexanoic acid
  20. 21. Isopropanol
  21. 22. Cyclobutanol
  22. 23. cyclohexanol
  23. 24. 2-methyl-2-propen-1-ol, and alkene/alcohol
  24. 25. Benzyl alcohol
  25. 26. Observe C-O fingerprint region Ethyl-vinyl ether/ether- alkene
  26. 27. Diethyl amine N-H
  27. 28. Butyl amine N-H H Observe a primary amine shows two absorptions, one for each hydrogen bonded to the electronegative atom Nitrogen
  28. 29. <ul><ul><li>Compound Bond Frequency (cm -1 ) </li></ul></ul><ul><li>Ketones and aldehydes </li></ul><ul><li>C=O 1760-1670 (strong, stretching) </li></ul><ul><li>Recall that aldehydes also show: </li></ul><ul><li>CHO two peaks 2850 and 2780 medium. </li></ul>Carbonyl family A
  29. 30. 3-pentanone / a ketone
  30. 31. 2-butanone- /a ketone
  31. 32. (Gas Phase) of Formaldehyde, H(C=O)H
  32. 33. 2-methylpropanal: an aldehyde
  33. 34. butyraldhyde CHO two peaks sharp, medium, around 2850 and 2780cm-1 .
  34. 35. <ul><li>Carboxylic acids, Esters </li></ul><ul><li>C=O 1760-1670 (strong, stretching) </li></ul><ul><li>C-O 1260-1000 ( strong, stret.) </li></ul><ul><li>Recall that Carboxylic acids also show: </li></ul><ul><li>O-H (H-bond formation) </li></ul><ul><li>3500-2500 (broad, stretching) </li></ul>Carbonyl/ Family B
  35. 36. Carboxylic acid
  36. 37. Benzoic acid O-H C=C C=O
  37. 38. Ester C=O and C-O C=O C-O
  38. 39. Ethyl acetate C=O C-O
  39. 40. <ul><li>amides </li></ul><ul><li>C=O 1760-1670 (strong, stretching) </li></ul><ul><li>C-O 1260-1000 ( strong, stret.) </li></ul><ul><li>Recall amide also show: </li></ul><ul><li>N-H as in amines but strong and broad for H-bond formation) </li></ul><ul><li>One peak for secondary amide, two peaks for primary amide </li></ul>Carbonyl family
  40. 41. Amide/acetamide C=O N-H H
  41. 42. Benzamide C=O C=C N-H N-H

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