Chem278 trans-cinnamic acid.docx

Nmr help provide evidence for suggesting the identity

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NMR help provide evidence for suggesting the identity of the first product to be 2,3-dibromo-3- phenylpropanoic acid. The hydrogen NMR shows six hydrogen environments. There is a very small, broad peak around 1PPM. This identifies the hydrogen environment on the alcohol group of the carboxylic acid. The hydrogen environments on each of the carbons containing bromines are at 5.337 and 4.911PPM. The hydrogen closest to the phenyl ring is slightly less shielded than the hydrogen closest to the acid because the phenyl has a higher value of shift. Also the J values suggest that the hydrogens are in the trans positon. The last hydrogen environments suggest the benzene ring hydrogens in the ortho, meta, and para position. Product 2 By E1 mechanism elimination the theoretical product is beta-Bromostyrene. The refractive index for beta-Bromostyrene is 1.607. The refractive index obtained from lab was 1.60156 which may suggest the identity of the product to be beta-Bromostyrene. In the IR spectroscopy we see that there are peaks at 3074.45cm -1 and 3023.5945cm -1 . In this region a hydrogen bonded to a doubly bonded carbon. The carbon here is sp 2 hybridized. Another important peak is at 729.56 cm -1 where there is the presence of a Bromine. The carbon NMR provides information that suggests there are six carbon environments in the product. The most deshielded carbon environment is attached to the bromine. Here it is being deshielded by the bromine’s tendency to parameter shift. The next environment at 132.380PPM
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is the other carbon environment on the alkene. Lastly there are environments that provide evidence of the phenyl ring in the product. 106.508PPM corresponds to the para position in the ring. The next peak at 128.322PPM is the meta position that is less shielded than the carbons at 128.986PPM because of the proximity to the ring. Lastly the carbon attaching the alkene chain is at 50.045PPM.
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  • Fall '08
  • CZU
  • Proton, Nuclear magnetic resonance, Proton NMR, aromatic compounds

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