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Organic Chemistry 326 SI
November 28, 2016
SN1, SN2, E1, E2
Final Exam Review
What is(are) the product(s) of this reaction?
I and II
III and IV
The product(s) of this reaction will be…
A and B
A, B and C
Which molecule was analyzed?
Review general chemistry
Photons: particles of electromagnetic radiation
Quantum: Discrete amount of energy in the photons
Wavelength (λ) = c / v
E = hv = hc /λ
What does IR spectroscopy analyze about a molecule?
The molecules molecular formula
The molecules carbon backbone (the C-C parent chain)
The functional groups present
All of the above
What type of motion is analyzed using IR spectroscopy?
Molecular ions rotation due to the radical cation that forms during fragmentation.
Unique proton vibrations
All of these
Used to determine the functional groups
Absorption of IR light changes the vibrational motions of the molecule
Include: Stretching and Bending
These are quantized (like stairs)
A molecule can only bend/stretch at specific frequencies corresponding to specific energies.
On the IR spectrum, where is the fingerprint region?
Between 4000 and 1500 cm-1
Between 400 - 1500 cm-1
Anything preceding the Base peak
Upstream from the last unique proton
IR Spectrum Absorptions Patterns
The peaks are used to determine the functional group
Between 4000 and 2500 cm-1
N-H and C-H (3300-3600 cm-1)
C-H (near 3000 cm-1)
Between 2500 and 2000 cm-1
Triple bonds (CC or CN)
Between 2000 and 1500 cm-1
Double bonds (C=O, C=N, C=C)
Less than 1500 cm-1
Fingerprint region: large variety of C-C, C-O, C-N, and C-X single bonds vibrate here
IR Spectrum Example
Trends: (Spring analogy)
Lighter atoms vibrate at higher frequencies (they absorb higher v )
Stronger bonds vibrate at higher frequencies (they absorb higher v )
C=C > C=C > C-C
Higher the percent s-character, the stronger the bond and the higher the wavenumber absorption
Csp3-H < Csp2-H < Csp-H
Old book table
Symmetrical, nonpolar bonds do not absorb in IR
IR inactive due to the inability to change in dipole moment during vibration
What bond has a lower wavenumber?
Both H and D have the same number of protons, therefore, the wavenumber is equal for both.
Which C-H bond absorbs the highest wavenumber?
Identify the Major Functional Groups Present
Answer: Csp2-H bonds, benzene ring, O-H bond
Application of MS and IR
Step 1: Use the molecular ion to determine possible molecular formulas. Use an exact mass to determine the molecular formula
Step 2: Calculate the number of degrees of unsaturation
Step 3: Determine what functional groups are present from the IR spectrum.
Nuclear Magnetic Resonance
1H NMR (proton NMR)
Number and type of hydrogen atoms in a molecule
13C NMR (carbon NMR)
Determine the type of carbon atoms
Magnetic field (B0) is used with electromagnetic radiation
Nuclear spins of the molecules are effected
Absorption of the radio waves cause the nucleus to “spin flip”
Move from a lower state of energy into an excited energy state
Applied magnetic field is used to orientate the nuclei
Stronger magnetic field results in an increased energy difference between the two nuclear spin states, thus stronger radiation is required.
All protons do not absorb the same frequency
Different environments required more/less energy needed to flip them, which have different signals
Four Major Features on these Spectrums:
1. Number of signals
Number of different Equivalent Protons
2. Position of signals
3. Intensity of signals
Number of Equivalent Protons
4. Spin-Spin splitting of signals
Non equivalent proton interaction
Which pair is correct?
Homotopic Protons – Identical (both structurally and eclectically)
Enantiotopic Protons – Not Identical structurally and but only eclectically
Diastereotopic Protons – Not Identical (neither structurally nor eclectically)
All are correct
Determining Proton Equivalence
Protons in the same environment give off the same signals
Different protons means replacing each H with X results in two different isomers
Determining Equivalent Protons
When the substitution of H with Z forms an enantiomer, the H are equivalent and they give off the same NMR signal.
When the substitution of H with Z forms a diastereomer, the two protons are not equivalent and they give off the two NMR signals.
How many different protons does CH3CH2OH have?
How many NMR signals will this molecule have?
End of IR light changes the vibrational motions of the molecule