Individual Discussion Spectroscopy Dry Lab Report
Individual Discussion Spectroscopy Dry Lab
Lab Section M5 - Group 6
January 24, 2015
Discussion
In this laboratory assignment, the spectroscopy data and molecular formula were given for 3 unknowns. An effort was made to conclusively identify these unknown samples using only the spectroscopy data, specifically 1H-NMR, 13C-NMR, and IR spectroscopy. Although mass spectrometry was given for the samples as well, its use was suggested only for confirmation, not identification, of the unknowns. Mass spectrometry was not included in the identification analysis of the compounds, however was used for confirmation of unknown #46. The spectroscopic data was analyzed using standard techniques, and the identity of the unknown samples were …show more content…
Taking the 3H integrated signal together with the 2H quadruplet signal, this combined integration and splitting pattern was indicative of a CH2-CH3 group being present on the unknown molecule. The three hydrogens on the end of the molecule have only 2 neighboring hydrogens; according to the n+1 rule, the 3H integrated hydrogens therefore appear as a triplet splitting pattern. The 2H integrated hydrogens have 5 neighboring hydrogens; according to the n+1 rule the 2H integrated hydrogens therefore appear as a multiplet splitting pattern. This is precisely what was seen on the sample NMR, please see Fig. 4 above. The NMR also revealed a 2H triplet in the 2.3 ppm, slightly downfield from the other two peaks. This indicates that 2 hydrogens are attached to a carbon with 2 hydrogen neighbors as well as to a carbon having no hydrogen attachments. This is indeed the case with molecule 4-octyne. Furthermore, the shift downfield would be expected, because the 2 protons there are close to a pi electron cloud of an sp-hybridized atom, and a proton close to an sp-hybridized atom would be expected to show this slight shift downfield.iv The two remaining signals found near 1.0 ppm and 1.5 ppm were indicative of CH2-CH3 sp3-hybridized signals, further matching the unknown molecule with the proposed structure. Therefore, the integration, splitting pattern, and …show more content…
The degrees of unsaturation formula, Eq. 1, was applied, and the molecule was found to have 4 degrees of unsaturation. : [(2 + 2(9) – 12)/2] = 4. It was noted that this is highly suggestive of a benzene ring, so the IR spectroscopy was analyzed for the presence of a benzene ring functional group. Aromatic benzene rings typically show IR peaks in the 1400-1500 and 3000-3100 cm-1 range. The signals seen on the IR of the unknown at 1454 and 3028 cm-1 range confirm the presence of an aromatic ring. Further analysis of the IR shows the presence of an OH functional group at 3339; OH functional groups typically appear at 3200-3500 cm-1 on IR. Notably absent on the IR are signals that would suggest double or triple bonds, see Table
Lab Section M5 - Group 6
January 24, 2015
Discussion
In this laboratory assignment, the spectroscopy data and molecular formula were given for 3 unknowns. An effort was made to conclusively identify these unknown samples using only the spectroscopy data, specifically 1H-NMR, 13C-NMR, and IR spectroscopy. Although mass spectrometry was given for the samples as well, its use was suggested only for confirmation, not identification, of the unknowns. Mass spectrometry was not included in the identification analysis of the compounds, however was used for confirmation of unknown #46. The spectroscopic data was analyzed using standard techniques, and the identity of the unknown samples were …show more content…
Taking the 3H integrated signal together with the 2H quadruplet signal, this combined integration and splitting pattern was indicative of a CH2-CH3 group being present on the unknown molecule. The three hydrogens on the end of the molecule have only 2 neighboring hydrogens; according to the n+1 rule, the 3H integrated hydrogens therefore appear as a triplet splitting pattern. The 2H integrated hydrogens have 5 neighboring hydrogens; according to the n+1 rule the 2H integrated hydrogens therefore appear as a multiplet splitting pattern. This is precisely what was seen on the sample NMR, please see Fig. 4 above. The NMR also revealed a 2H triplet in the 2.3 ppm, slightly downfield from the other two peaks. This indicates that 2 hydrogens are attached to a carbon with 2 hydrogen neighbors as well as to a carbon having no hydrogen attachments. This is indeed the case with molecule 4-octyne. Furthermore, the shift downfield would be expected, because the 2 protons there are close to a pi electron cloud of an sp-hybridized atom, and a proton close to an sp-hybridized atom would be expected to show this slight shift downfield.iv The two remaining signals found near 1.0 ppm and 1.5 ppm were indicative of CH2-CH3 sp3-hybridized signals, further matching the unknown molecule with the proposed structure. Therefore, the integration, splitting pattern, and …show more content…
The degrees of unsaturation formula, Eq. 1, was applied, and the molecule was found to have 4 degrees of unsaturation. : [(2 + 2(9) – 12)/2] = 4. It was noted that this is highly suggestive of a benzene ring, so the IR spectroscopy was analyzed for the presence of a benzene ring functional group. Aromatic benzene rings typically show IR peaks in the 1400-1500 and 3000-3100 cm-1 range. The signals seen on the IR of the unknown at 1454 and 3028 cm-1 range confirm the presence of an aromatic ring. Further analysis of the IR shows the presence of an OH functional group at 3339; OH functional groups typically appear at 3200-3500 cm-1 on IR. Notably absent on the IR are signals that would suggest double or triple bonds, see Table