Chem 233 Final – Prelecture
Exam Study Guide
Mass spectrometry separates compounds based on what characteristic?
mass/charge ratio
charge/mass ratio
mass
charge - ANSWER mass/charge ratio
Electrospray ionization mass spectroscopy often results in analyte molecules
fragmenting.
true
false - ANSWER false
Which of the following types of carbonyl would generally have a stretch located
below 1700 cm-1?
amide
aldehyde
ketone
carboxylic acid
ester - ANSWER amide
The fingerprint region is a difficult to interpret area of an IR Spectrum.
true
false - ANSWER true
The stretch for a C-H bond where the carbon is sp2 hybridized would be located
where on an IR spectrum? (
at approximately 2700 cm-1
just above 3000 cm-1
at approximately 3300 cm-1
just below 3000 cm-1 - ANSWER just above 3000cm-1
proton sets - ANSWER protons that are in the same environment will belong to
the same proton set, in an HNMR spectra.
, Integration value in H NMR - ANSWER The integration is the area under each
absorption peak (resonance). The calculated area under each peak is
proportional to the relative # of protons giving rise to each peak. Thus,
integration indicates the relative # of protons in each set in the molecule. For
this class, it is the number of protons attached to that element.
position on the H NMR specta - ANSWER hydrogen atoms that are closer to
electron withdrawing groups are further downfield as compared to hydrogen
atoms farther away from the electron withdrawing groups.
multiplicity H NMR - ANSWER no of peaks in any set of the H NMR, also it is also
one more than the neighboring carbons.
Proton A couples to Proton B. Proton A posseses a J-value of 3.0 Hz. What do
you expect the J-value Proton B posseses to be? (1 pt)
Less than 3.0 Hz
Greater than 3.0 Hz
No J-value because coupling is only one-way
3.0 Hz - ANSWER 3.0 Hz
J value - ANSWER The energy difference between spin states caused by spin-
spin coupling. Also the chemical shift difference between the lines in a split NMR
signal due to spin-spin coupling. Take the difference between any two adjacent
peaks and multiply that difference by the MHz of the spectrometer, round
answer to tenths.
where are carbonyl signals found in C NMR? - ANSWER close to 207 ppm
signals that come up for alkene and aromatic carbons - ANSWER 120ppm
122ppm
127ppm
135ppm
You suspect an unknown compound possesses a disubstituted alkene. Select all
pieces of spectroscopic information that must be present if your hypothesis is
correct.
stretch in the IR spectrum at approximately 2200 cm-1
stretch in the IR spectrum at approximately 1650 cm-1
signals in the 1H NMR spectrum around 5.5 ppm
signals in the 13C NMR spectrum around 140 ppm
stretch in the IR spectrum at approximately 1700 cm-1
signals in the 1H NMR spectrum around 10.0 ppm
broad stretch in the IR spectrum at approximately 3500 cm-1
Exam Study Guide
Mass spectrometry separates compounds based on what characteristic?
mass/charge ratio
charge/mass ratio
mass
charge - ANSWER mass/charge ratio
Electrospray ionization mass spectroscopy often results in analyte molecules
fragmenting.
true
false - ANSWER false
Which of the following types of carbonyl would generally have a stretch located
below 1700 cm-1?
amide
aldehyde
ketone
carboxylic acid
ester - ANSWER amide
The fingerprint region is a difficult to interpret area of an IR Spectrum.
true
false - ANSWER true
The stretch for a C-H bond where the carbon is sp2 hybridized would be located
where on an IR spectrum? (
at approximately 2700 cm-1
just above 3000 cm-1
at approximately 3300 cm-1
just below 3000 cm-1 - ANSWER just above 3000cm-1
proton sets - ANSWER protons that are in the same environment will belong to
the same proton set, in an HNMR spectra.
, Integration value in H NMR - ANSWER The integration is the area under each
absorption peak (resonance). The calculated area under each peak is
proportional to the relative # of protons giving rise to each peak. Thus,
integration indicates the relative # of protons in each set in the molecule. For
this class, it is the number of protons attached to that element.
position on the H NMR specta - ANSWER hydrogen atoms that are closer to
electron withdrawing groups are further downfield as compared to hydrogen
atoms farther away from the electron withdrawing groups.
multiplicity H NMR - ANSWER no of peaks in any set of the H NMR, also it is also
one more than the neighboring carbons.
Proton A couples to Proton B. Proton A posseses a J-value of 3.0 Hz. What do
you expect the J-value Proton B posseses to be? (1 pt)
Less than 3.0 Hz
Greater than 3.0 Hz
No J-value because coupling is only one-way
3.0 Hz - ANSWER 3.0 Hz
J value - ANSWER The energy difference between spin states caused by spin-
spin coupling. Also the chemical shift difference between the lines in a split NMR
signal due to spin-spin coupling. Take the difference between any two adjacent
peaks and multiply that difference by the MHz of the spectrometer, round
answer to tenths.
where are carbonyl signals found in C NMR? - ANSWER close to 207 ppm
signals that come up for alkene and aromatic carbons - ANSWER 120ppm
122ppm
127ppm
135ppm
You suspect an unknown compound possesses a disubstituted alkene. Select all
pieces of spectroscopic information that must be present if your hypothesis is
correct.
stretch in the IR spectrum at approximately 2200 cm-1
stretch in the IR spectrum at approximately 1650 cm-1
signals in the 1H NMR spectrum around 5.5 ppm
signals in the 13C NMR spectrum around 140 ppm
stretch in the IR spectrum at approximately 1700 cm-1
signals in the 1H NMR spectrum around 10.0 ppm
broad stretch in the IR spectrum at approximately 3500 cm-1
