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Elucidating a Chemical Structure of Unknown B
Elucidating a Chemical Structure of Unknown B
Robert Michaud, Terry Cullen, Mac kenzie Dufour, Fabrice Iraduha, and Abil Teshome
Saint Joseph’s College, Standish, ME 04049
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Elucidating a Chemical Structure of Unknown B
Elucidating a Chemical Structure of Unknown B
Procedure
We ran a total of six tests. First we took the IR of unknown B. We took a melting point of the
unknown. Next we took the unknown B and added deuterochloroform until it was saturated
for use in the next tests. We ran a total of four tests on the NMR, a 1H NMR, 13C NMR, Cosy,
and a Dept. We received the molecular weight and formula. We then used this information to
determine the chemical structure of Unknown B.
Figures
O
CH3
14
H3C
10
9
N
13
8
N
7
1
2
O
11
N
3
4
N
5
CH3
12
Figure 1. A graphical representation of Unknown B.
6
H
6a
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Elucidating a Chemical Structure of Unknown B
Figure 2. Ball and stick representation of Unknown B. In this representation, the electron
density is represented, showing the possible electron flow.
Results
After analysis of the data collected, we concluded that the compound was caffeine.
Analytical techniques
Molecular Formula
C 8 H 10 N 4 O 2
Molecular Weight
194.19g
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Elucidating a Chemical Structure of Unknown B
Index of Hydrogen Deficiency
Carbons = 8
Index of Hydrogen Deficiency =
(# Saturated H) – (# Actual H)
--------------------------------------- =
2
18-10
------2
IHD = 4
Melting Point
The melting point of the unknown was around 225°C and the actual melting point for caffeine is
227°C.
IR Spectra
From the IR Spectra, we found a peak at 1651.48cm-1, which indicates a presence of a carbonyl
group. Another peak appeared at 1696.97 cm-1 indicating the presence of a possible amide
group.
1H NMR Shifts
We found a peak at 7.9ppm and determined that to be H 6a on figure 1. The peak is due to the
double bond between the C and N, which causes the high down shift. The next peak is at
4.2ppm, which indicates H’s on C 13 bonded to N 7 in the cyclopentene. There were two other
significant peaks with similar shifts, one was at 3.6ppm and the other was at 3.4ppm. These
closely related shifts indicate a relationship between the hydrogen’s. They both are near
carbonyls. The 3.4ppm is the H’s bonded to the C 12. The more upshift quality is due to the
reduction of the electron density caused by the carbonyl and the double bond of the N bonded
to the C. The 3.6 is the H’s bonded to C 10. This is surrounded by two carbonyls which gives
these H’s a more down shift quality.
13C NMR Shifts
There was a lot of noise on this scan, but through refinement of the scan, four shifts were
determined. The shit at 141ppm supports a heteroaromatic structure. With the presence of
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Elucidating a Chemical Structure of Unknown B
the N this would support the N’s presence in the aromatic system. The next shift at 33ppm
indicates a C-N-R2 bonding. This is seen on C 13, which is bonded to N 7 and two R groups.
There are two similar shifts at 29ppm and 27ppm, these shifts are comparable to the C-N-R2
group. The difference in the shifts is due to the presence of a carbonyl group for one of the R
groups. This causes the upfield shift indicated by the 29ppm and 27ppm peaks.
Cosy
After analyzing the Cosy graph, we determined that the C 13 and C 6 are adjacent. This was
done by finding one peak that was off the diagonal peaks. Using the diagonal peaks as a
reference point, we traced horizontally and discovered one significant peak at 7.9ppm. After
tracing the two overlapping 7.9ppm peaks to their intercept 4.2ppm, we determined that C 13
and C 6 are adjacent carbons based on their H configuration.
Dept
Due to the noise on the spectra this spectra was inconclusive.
Conclusion
Using spectroscopic techniques (IR, 1H NMR, 13C NMR, and Cosy) we were able to
conclusively determine that Unknown B is Caffeine. We used a reference to determine the
similarities in the structures. The IR helped narrow our possibilities into general functional
groups, which we used with the NMR to help identify structures. The Cosy was useful to
indicate the adjacent C 13 and C 6. Additionally we used the 1H NMR to determine the
different functional groups and conclude the heteroaromaticity. After a complete analysis, the
mysterious, unknown, white powder was determined to be Caffeine.
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Elucidating a Chemical Structure of Unknown B
Appendix
IR Spectra
1H Spectra
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Elucidating a Chemical Structure of Unknown B
13C Spectra
Cosy
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Elucidating a Chemical Structure of Unknown B
Dept