Week 1 for friday key finished verion
Answer the following for Friday…….
1. a. Draw the electromagnetic spectrum.
——Increasing energy
b. Label the trends for energy, wavelength, and frequency.
c. Wavenumbers (1/cm) are units of Frequency
d. Which region of the electromagnetic spectrum when absorbed by a molecule will result in vibrational stretching
and bending modes of motion? Infrared
2. Summarize the relationship between the relative rates of vibration of a bond (or spring):
a. that result from using two different masses. When small masses are present, they will vibrate faster than a heavy
atom (this is because H has a large mass difference from the heavier atoms – reduced mass)
b. that results from having bonds (springs) with different strengths (spring constants). The stronger the spring or
bond, the faster the vibration observed
3. a. Label the diagnostic peaks present on the spectra and identify the stretches observed.
b. What functional groups are present?__Primary amine and sp2C-H bonds
c. What functional groups are absent?__Alcohols, secondary amines, spC-H bonds, sp3C-H bonds, C(triple bond)C or N,
C=O
d. Can you determine the structure of the molecule based on its infrared spectrum alone?No only the functional groups
present
3.(continued)
e. For each structure shown, provide a list of peaks that you would expect to see from that molecule.
a. OH stretching broad 3400cm-1
aromatic sp2C-H 3000-3100cm-1
Aromatic C=C may be too close to fingerprint region to worry with 1650cm-1 shifted lower by resonance.
b. C=O around 1700cm-1
sp3C-H 2850-3000cm-1
c. Secondary amine N-H stretching moderately broadened around 3300-3400cm-1
sp3C-H 2850-3000cm-1
d. Primary amine NH2 – double peak, moderately broadened around 3300-3400cm-1
aromatic sp2C-H 3000-3100cm-1
Aromatic C=C may be too close to fingerprint region to worry with 1650cm-1 shifted lower by resonance.
e. OH stretching VERY broad 3000cm-1 (2800-3300cm-1)
C=O around 1700cm-1
sp3C-H 2850-3000cm-1
f. Primary amide NH2 – double peak, moderately broadened around 3100-3400cm-1
C=O around 1700cm-1
sp3C-H 2850-3000cm-1
g. Primary amine NH2 – double peak, moderately broadened around 3300-3400cm-1
sp3C-H 2850-3000cm-1
h. OH stretching broad 3400cm-1
sp3C-H 2850-3000cm-1
i. Secondary amine N-H stretching moderately broadened around 3300-3400cm-1
aromatic sp2C-H 3000-3100cm-1
Aromatic C=C may be too close to fingerprint region to worry with 1650cm-1 shifted lower by resonance.
j. C=O around 1700cm-1
aromatic sp2C-H 3000-3100cm-1
Aromatic C=C may be too close to fingerprint region to worry with 1650cm-1 shifted lower by resonance.
k. Secondary amide NH –single peak, moderately broadened around 3100-3400cm-1
C=O around 1700cm-1
sp3C-H 2850-3000cm-1
l. OH stretching VERY broad 3000cm-1 (2800-3300cm-1)
C=O around 1700cm-1
aromatic sp2C-H 3000-3100cm-1
Aromatic C=C may be too close to fingerprint region to worry with 1650cm-1 shifted lower by resonance.
m. spC-H stretch around 3200-3300cm-1
C(triple bond)C weak stretch around 2200cm-1
sp3C-H 2850-3000cm-1
n. Primary amide NH2 – double peak, moderately broadened around 3100-3400cm-1
C=O around 1700cm-1
aromatic sp2C-H 3000-3100cm-1
Aromatic C=C may be too close to fingerprint region to worry with 1650cm-1 shifted lower by resonance.
o. C(triple bond)N moderate stretch around 2250cm-1
sp3C-H 2850-3000cm-1
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
k.
l.
m.
n.
o.
p. Which molecule was used to create the spectra above? D
4. In reviewing Sections 8 – 12 for Friday, fill in the following blanks to make true statements about mass spectroscopy.
In a mass spectrometer:
a. A compound is Vaporized, then it passes near a hot filament where it gets Ionized before
undergoing Fragmentation.
b. The resulting cations are separated based on their Mass to Change ratio. The z in this m/z ratio stands
for the Charge.
c. The masses of the cations are Separated and graphed.
d. EI is the most common type of mass spectroscopy. What does EI stand for? Electron Impact or Electron Ionization
e. The molecular ion is written as [M]+’ and has the same ‘exact mass’ as the initial molecule. The mass of the lost
Electron is considered negligible.
f. Another name for the radical cation generated from the ionization of a molecule is the Molecular ion or Parent ion
g. How do you identify the base peak? Tallest peak on the spectra.
h. When a radical cation fragments, the Positively charged cation fragment will be accelerated towards the magnet
where its
path is deflected to separate out the fragments by Mass to Change ratio before they reach the detector.
The Radical fragment is neutral and is not detected.
i. If the molecular ion’s m/z is an odd number, that is the indication that there is a Nitrogen present.
5. Analyze the spectra shown.
a. What is the m/z of the base peak?____43______ b. What is the m/z of the parent ion?___78_____
c. There is a halogen present. Which one?___________________chlorine
d. Which peak(s) indicate the presence of a halogen?___63/65 and 78/80
e. What is the mass of the molecular ion?___________78
f. Assume the molecule is an alkyl halide, what is
the molecular formula of the molecule being
analyzed?___________C3H7Cl
g. Provide one possibility for the structure of the
molecule.
1-chloropropane
2-chloropropane
…
