In this experiment, a Wittig reaction was performed in order to synthesize a mixtures of (E)- and (Z)-stilbene. Photoisomerization was then performed to isolate (E)-stilbene by transforming (Z)-stilbene into (E)-stilbene. The presence of the products throughout the experiment was monitored by 1H NMR. The final product was then characterized by 1H NMR, IR and its melting point.
During synthesize of the product, the appearance of the reaction mixture changed. The main solution containing dicholormethane, benzyltriphenylphosphorium and benzaldehyde was cloudy and white. This solution changed colors when the sodium hydroxide solution was added. After only a small amount of sodium hydroxide solution was added, the reaction solution became …show more content…
IR was also obtained for the final product. Overall, the 1H NMR data shows a decrease in (Z)-stilbene and an increases in (E)-stilbene. For the first fraction, the crude product, a ratio of (E)-stilbene to (Z)-stilbene was 1:1. This means that the crude mixture was half of the trans isomer and half the cis isomer. This ratio was determined by looking at the two singlets in the spectra RM-09-1 representing the protons on alkene double bond. The singlets in RM-09-1 were found at 7.11 ppm and 6.59 ppm. The reported values, found on SDBS, for the chemical shifts of these singlets were 6.57 ppm for (Z)-stilbene and 7.15 ppm for (E)-stilbene. These peaks also determined the ratio of isomers for the second and third fractions as well. In the spectra RM-09-2, the ratio was determined to be 4:3. The singlets on this spectrum were found at 7.11 ppm and 6.59 ppm as well. This means that in the crude isomerized product, (E)-stilbene was of greater presence than (Z)-stilbene. This is an appropriate observation, because the purpose of photoisomerization was to transform the cis isomer into the trans isomer. This occurrence also was shown in the 1H NMR for the third fraction. (E)-stilbene increased in presence, while (Z)-stilbene decreased in presence. This ratio was found to be 7:5, and was based upon the peaks at 7.10 ppm
During synthesize of the product, the appearance of the reaction mixture changed. The main solution containing dicholormethane, benzyltriphenylphosphorium and benzaldehyde was cloudy and white. This solution changed colors when the sodium hydroxide solution was added. After only a small amount of sodium hydroxide solution was added, the reaction solution became …show more content…
IR was also obtained for the final product. Overall, the 1H NMR data shows a decrease in (Z)-stilbene and an increases in (E)-stilbene. For the first fraction, the crude product, a ratio of (E)-stilbene to (Z)-stilbene was 1:1. This means that the crude mixture was half of the trans isomer and half the cis isomer. This ratio was determined by looking at the two singlets in the spectra RM-09-1 representing the protons on alkene double bond. The singlets in RM-09-1 were found at 7.11 ppm and 6.59 ppm. The reported values, found on SDBS, for the chemical shifts of these singlets were 6.57 ppm for (Z)-stilbene and 7.15 ppm for (E)-stilbene. These peaks also determined the ratio of isomers for the second and third fractions as well. In the spectra RM-09-2, the ratio was determined to be 4:3. The singlets on this spectrum were found at 7.11 ppm and 6.59 ppm as well. This means that in the crude isomerized product, (E)-stilbene was of greater presence than (Z)-stilbene. This is an appropriate observation, because the purpose of photoisomerization was to transform the cis isomer into the trans isomer. This occurrence also was shown in the 1H NMR for the third fraction. (E)-stilbene increased in presence, while (Z)-stilbene decreased in presence. This ratio was found to be 7:5, and was based upon the peaks at 7.10 ppm