1. 8.13 Predicting Subst. vs. Elim.
Analyze the function of the reagent (nucleophile and/ or base)
Analyze the substrate (1°, 2°, or 3°)
Copyright 2012 John Wiley & Sons, Inc.

2. 8.13 Predicting Subst. vs. Elim.
Analyze the function of the reagent (nucleophile and/ or base)
Analyze the substrate (1°, 2°, or 3°)
Copyright 2012 John Wiley & Sons, Inc.

3. 8.13 Predicting Subst. vs. Elim.
Analyze the function of the reagent (nucleophile and/ or base)
Analyze the substrate (1°, 2°, or 3°)
Copyright 2012 John Wiley & Sons, Inc.

4. 8.13 Predicting Subst. vs. Elim.
Analyze the function of the reagent (nucleophile and/ or base)
Analyze the substrate (1°, 2°, or 3°)
Practice with SkillBuilder 8.11
Copyright 2012 John Wiley & Sons, Inc.

5. 8.14 Predicting Products
Analyze the function of the reagent (nucleophile and/ or base)
Analyze the substrate (1°, 2°, or 3°)
Consider regiochemistry and stereochemistry
Copyright 2012 John Wiley & Sons, Inc.

6. 8.14 Predicting Products Consider regiochemistry and stereochemistry
Practice with SkillBuilder 8.12
Copyright 2012 John Wiley & Sons, Inc.

7. 15.1 Introduction to Spectroscopy
Spectroscopy involves an interaction between matter and light (electromagnetic radiation)
Light can be thought of as waves of energy or packets (particles) of energy called photons
Properties of light waves include wavelength and frequency
Is wavelength directly or inversely proportional to energy? WHY?
Is frequency directly or inversely proportional to energy? WHY?
Copyright 2012 John Wiley & Sons, Inc.

8. 15.1 Introduction to Spectroscopy
There are many wavelengths of light that can not be observed with your eyes
Copyright 2012 John Wiley & Sons, Inc.

9. 15.1 Introduction to Spectroscopy
When light interacts with molecules, the effect depends on the wavelength of light used
This chapter focuses on IR spectroscopy
Copyright 2012 John Wiley & Sons, Inc.

10. 15.1 Introduction to Spectroscopy
Matter exhibits particle-like properties
On the macroscopic scale, matter appears to exhibit continuous behavior rather than quantum behavior
Consider the example of an engine powering the rotation of a tire. The tire should be able to rotate at nearly any rate
Matter also exhibits wave-like properties as we learned in section 1.6
Matter on the molecular scale exhibits quantum behavior
A molecule will only rotate or vibrate at certain rates (energies)
Copyright 2012 John Wiley & Sons, Inc.

11. 15.1 Introduction to Spectroscopy
For each of the types of molecular motion/energy below, describe how it is quantized
Rotation
Vibration
Energy of electrons
Copyright 2012 John Wiley & Sons, Inc.

12. 15.1 Introduction to Spectroscopy
For each different bond, vibrational energy levels are separated by gaps (quantized)
If a photon of light strikes the molecule with the exact amount of energy needed, a molecular vibration will occur
Energy is eventually released from the molecule generally in the form of heat
Infrared (IR) Light generally causes molecular vibration
HOW might IR light absorbed give you information about a molecule’s structure
Copyright 2012 John Wiley & Sons, Inc.

13. 15.2 IR Spectroscopy
Molecular bonds can vibrate by stretching or by bending in a number of ways
This chapter will focus mostly on stretching frequencies
WHY do objects emit IR light?
WHY do some objects emit more IR radiation than others?
WHERE does that light come from?
Copyright 2012 John Wiley & Sons, Inc.

14. 15.2 IR Spectroscopy
Some night vision goggles can detect IR light that is emitted
IR or thermal imaging is also used to detect breast cancer
Copyright 2012 John Wiley & Sons, Inc.

15. 15.2 IR Spectroscopy
The energy necessary to cause vibration depends on the type of bond
Copyright 2012 John Wiley & Sons, Inc.

16. 15.2 IR Spectroscopy
An IR spectrophotometer irradiates a sample with all frequencies of IR light
The frequencies that are absorbed by the sample tell us the types of bonds (functional groups) that are present
How do we measure the frequencies that are absorbed?
Most commonly, samples are deposited neat on a salt (NaCl) plate. WHY is salt used?
Alternatively, the compound may be dissolved in a solvent or embedded in a KBr pellet
Copyright 2012 John Wiley & Sons, Inc.

17. 15.2 IR Spectroscopy
In the IR spectrum below, WHAT is % transmittance and how does it relate to molecular structure?
Copyright 2012 John Wiley & Sons, Inc.

18. 15.2 IR Spectroscopy Analyze the units for the wavenumber,
ν = frequency and c = the speed of light
Copyright 2012 John Wiley & Sons, Inc.

19. 15.2 IR Spectroscopy HOW are wavelength and wavenumber different?
HOW are wavenumbers and energy related?
Copyright 2012 John Wiley & Sons, Inc.

20. 15.2 IR Spectroscopy
A signal on the IR spectrum has three important characteristics: wavenumber, intensity, and shape
Copyright 2012 John Wiley & Sons, Inc.

21. 15.3 IR Signal Wavenumber
The wavenumber for a stretching vibration depends on the bond strength and the mass of the atoms bonded together
Should bonds between heavier atoms require higher or lower wavenumber IR light to stretch?
Copyright 2012 John Wiley & Sons, Inc.

22. 15.3 IR Signal Wavenumber
Rationalize the trends below using the wavenumber formula
Copyright 2012 John Wiley & Sons, Inc.

23. 15.3 IR Signal Wavenumber
The wavenumber formula and empirical observations allow us to designate regions as representing specific types of bonds
Explain the regions above
Copyright 2012 John Wiley & Sons, Inc.

24. 15.3 IR Signal Wavenumber
The region above 1500 cm-1 is called the diagnostic region. WHY?
The region below 1500 cm-1 is called the fingerprint region. WHY?
Copyright 2012 John Wiley & Sons, Inc.

25. 15.3 IR Signal Wavenumber
Analyze the diagnostic and fingerprint regions below
Copyright 2012 John Wiley & Sons, Inc.

26. 15.3 IR Signal Wavenumber
Analyze the diagnostic and fingerprint regions below
Copyright 2012 John Wiley & Sons, Inc.

27. 15.3 IR Signal Wavenumber Compare the IR spectra
Copyright 2012 John Wiley & Sons, Inc.

28. 15.3 IR Signal Wavenumber
Given the formula below and the given IR data, predict whether a C-H or O-H bond is stronger
C-H stretch ≈ 3000 cm-1
O-H stretch ≈ 3400 cm-1
Practice with conceptual checkpoint 15.1
Copyright 2012 John Wiley & Sons, Inc.

29. 15.3 IR Signal Wavenumber Compare the IR stretching wavenumbers below
Are the differences due to mass or bond strength?
Which bond is strongest, and WHY?
Copyright 2012 John Wiley & Sons, Inc.

30. 15.3 IR Signal Wavenumber
Note how the region ≈3000 cm-1 in the IR spectrum can give information about the functional groups present
Copyright 2012 John Wiley & Sons, Inc.

31. 15.3 IR Signal Wavenumber
Is it possible that an alkene or alkyne could give an IR spectra without any signals above 3000 cm-1?
Predict the wavenumbers that would result (if any) above 3000 cm-1 for the molecules below
Practice with conceptual checkpoint 15.2
Copyright 2012 John Wiley & Sons, Inc.

32. 15.3 IR Signal Wavenumber
Resonance can affect the wavenumber of a stretching signal
Consider a carbonyl that has two resonance contributors
If there were more contributors with C-O single bond character than C=O double bond character, how would that affect the wavenumber?
Copyright 2012 John Wiley & Sons, Inc.

33. 15.3 IR Signal Wavenumber
Use the given examples to explain HOW and WHY the conjugation and the –OR group affect resonance and thus the IR signal?
Practice with conceptual checkpoint 15.3
Copyright 2012 John Wiley & Sons, Inc.

34. 15.4 IR Signal Strength The strength of IR signals can vary
Copyright 2012 John Wiley & Sons, Inc.

35. 15.4 IR Signal Strength
When a bond undergoes a stretching vibration, its dipole moment also oscillates
Recall the formula for dipole moment includes the distance between the partial charges,
The oscillating dipole moment creates an electrical field surrounding the bond
Copyright 2012 John Wiley & Sons, Inc.

36. 15.4 IR Signal Strength
The more polar the bond, the greater the opportunity for interaction between the waves of the electrical field and the IR radiation
Greater bond polarity = stronger IR signals
Copyright 2012 John Wiley & Sons, Inc.

37. 15.4 IR Signal Strength
Note the general strength of the C=O stretching signal vs. the C=C stretching signal
Imagine a symmetrical molecule with a completely nonpolar C=C bond: 2,3-dimethyl-2-butene
2,3-dimethyl-2-butene does not give an IR signal in the cm-1 region
Copyright 2012 John Wiley & Sons, Inc.

38. 15.4 IR Signal Strength
Stronger signals are also observed when there are multiple bonds of the same type vibrating
Although C-H bonds are not very polar, they often give very strong signals, WHY?
Because sample concentration can affect signal strength, the Intoxilyzer 5000 can be used to determine blood alcohol levels be analyzing the strength of C-H bond stretching in blood samples
Practice with conceptual checkpoints 15.5 – 15.7
Copyright 2012 John Wiley & Sons, Inc.

39. Study Guide for sections 8.13-8.14, 15.1-15.4
DAY 19, Terms to know:
Sections , Spectroscopy, photons, wavelength, frequency, quantum behavior, spectrophotometer, % transmittance, wavenumber
DAY 19, Specific outcomes and skills that may be tested on exam 3:
Sections ,
Be able to explain the relationships between wavelength, frequency, and energy for light.
Be able to rank the different categories of light radiowaves, microwaves, IR, UV, etc.) based on energy, wavelength, or frequency.
Be able to explain the differences between continuous behavior and quantum behavior.
Be able to explain how vibration, rotation, and energy of electrons are all quantized.
Be able to explain what happens in general when IR light hits a molecule.
Be able to explain what happens to the energy when a molecule excited by IR light relaxes.
Be able to explain why objects emit IR radiation how that relates to temperature.
Be able to give a description of how a spectrophotometer works and how it gives information about the structure of a compound.
Be able to explain how wavenumber and intensity relate to the type of bond absorbing the radiation.
Be able to explain how bond strength and length relate to the wavenumber observed in stretching IR frequencies.
Be able to analyze an IR spectra and pick out the most relevant peaks and determine what information about the molecule can be determined from the analysis of those peaks.
Be able to explain the significance of the region around 3000 cm-1 and how that relates to the type of atom and hybridization of the atom bonded to a hydrogen atom.
Be able to explain how the intensity of a signal relates to the polarity of the bond and the number of bonds present giving the signal.
Klein, Organic Chemistry 2e

40. Practice Problems for sections 8.13-8.14, 15.1-15.4
Complete these problems outside of class until you are confident you have learned the SKILLS in this section outlined on the study guide and we will review some of them next class period
Klein, Organic Chemistry 2e

41. Prep for Day 20 Must Watch videos: Other helpful videos:
(IR: shape)
(IR: practice)
(mass spec)
(ionization and fragmentation in mass spec)
Other helpful videos:
(IR: practice)
(gas chromatography)
Read sections
Klein, Organic Chemistry 2e