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Infrared Radiation: Molecular Vibrations. Electromagnetic Radiation: Light, Energy, Heat IR Tutor:

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Presentation on theme: "Infrared Radiation: Molecular Vibrations. Electromagnetic Radiation: Light, Energy, Heat IR Tutor:"— Presentation transcript:

1 Infrared Radiation: Molecular Vibrations

2 Electromagnetic Radiation: Light, Energy, Heat IR Tutor:

3 What do the suns energy, a molecules shape and a TV remote have to do with greenhouse gases?

4 Infrared Absorbance

5 Remote TV

6 Infrared Absorbance Sample TV Remote

7 Infrared Absorbance & Molecular Vibrations for CCl 4 Stretching & Bending

8 Infrared Spectroscopy

9 Infrared Absorbance

10 IR- Empirical Comparisons Identifying functional groups in organic molecules

11 Region of infrared that is most useful lies between m ( cm -1 ) depends on transitions between vibrational energy states Stretching: higher energy / higher wave number (cm -1 ) Bending: lower energy / lower wave number (cm -1 ) Infrared Spectroscopy

12 A bond must have a dipole or an induced dipole in order to have an absorbance in the IR spectrum. When the bond stretches, the increasing distance between the atoms increases the dipole moment. Therefore, the greater the dipole, the more intense the absorption. (i.e., The greater the molar extinction coefficient ( ) in Beers law, A = bc.

13 The presence & absence of absorption bands must be considered in identifying a possible structure in IR spectroscopy. Empiricism is critical to successful identification. NOTE: Bonds which lack dipole moments are not detected. Analyzing Structure: Functions & Infrared Spectra The molecular formula is a critical piece of information, which limits the functional possibilities.

14 Structural/Functional Components

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16 The peaks are quantized absorption bands corresponding to molecular stretching and bending vibrations An Infrared Spectrum

17 The fingerprint region The functional group stretching region

18 Structural unitFrequency, cm -1 Stretching vibrations (single bonds) OH (alcohols) OH (carboxylic acids) Infrared Absorption Frequencies First examine the absorption bands in the vicinity of cm –1

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20 Structural unitFrequency, cm -1 Stretching vibrations (single bonds) sp CH sp 2 CH sp 3 CH sp 2 CO1200 sp 3 CO Infrared Absorption Frequencies

21 Structural unitFrequency, cm -1 Stretching vibrations (carbonyl groups) Aldehydes and ketones Carboxylic acids Acid anhydrides and Esters Amides Infrared Absorption Frequencies C O

22 Cyclic aliphatic ketone

23 Mono substituted aromatic methyl ketone

24 Mono substituted aromatic ketone

25 Aliphatic ester I

26 Aliphatic ester II

27 Aliphatic ester III

28 Mono substituted aromatic ester

29 Mono substituted aromatic conjugated ester

30 Structural unitFrequency, cm -1 Stretching vibrations (single bonds) sp 2 CO1200 sp 3 CO Infrared Absorption Frequencies

31 Dihexyl Ether ~1100 cm cm -1

32 ~1200 cm -1 Carboxylic Acid

33 Distinctive Stretch of C–H Bond in an Aldehyde (the waggle vibration)

34 Aliphatic aldehyde

35 Mono-substituted aromatic aldehyde

36 Mono substituted aromatic ester

37 Para di-substituted aromatic ether & aldehyde

38 Infrared Spectroscopy Common Functional Groups Handout Handout

39 Acetate Esters: Smell / Pheromones Pheromone Synthesis [20:40-23:51]

40 Infrared Spectroscopy Common Functional Groups Questions

41 A)benzyl alcohol B)2,4,6-cycloheptaheptatrien-1-one C)acetophenone D)benzaldehyde E)phenylacetic acid C7H6OC7H6OC7H6OC7H6O Question #1 Identify the compound from the IR above.

42 Question #2 C 10 H 12 O Identify the compound from the IR above. A)2,4,5-trimethylbenzaldehyde B)p-allylanisole C)2-allyl-4methylphenol D)1-phenyl-2-butanone

43 Question #3 C3H4OC3H4OC3H4OC3H4O A)cyclopropanone B)propynol C)acrylaldehyde D)propenoic acid Identify the compound from the IR above.

44 Question #4 A)methylbenzoate B)o-hydroxyacetophenone C)o-toluic acid D)p-anisaldehyde (p-methoxybenzaldehyde) Identify the compound from the IR above. C8H8O2C8H8O2C8H8O2C8H8O2

45 Question #5 A)benzylformate B)o-hydroxyacetophenone C)2-methoxytropone D)p-toluic acid E)o-anisaldehyde (p-methoxybenzaldehyde) Identify the compound from the IR above. C8H8O2C8H8O2C8H8O2C8H8O2


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