(1 pts) Literature melting point of (E,E)-1,4-diphenyl-1,3-butadiene From the procedure 10. Measure the melting point of both your crude product and your recrystallized product. Record these values on the data sheet. 139.0- 148.7°C Melting point of crude product: Melting point of recrystallized product: 145.1 – 148.4 °C (0.5pts) Melting point of crude product (°C) 139.0-148.7 Saved (0.5pts) Melting point of recrystallized product (°C) 145.1-148.4 Does the melting point obtained for your product indicate that your sample is (E,E)-1,4-diphenyl-1,3-butadiene? Or a mixture of isomers? Normal . BIU X2 X – === f TX (2pts) Was there a difference in the melting point of the crude and the melting point of the recrystallized product?
The Correct Answer and Explanation is:
Correct Answer:
Yes, the melting point of the recrystallized product suggests that the sample is predominantly (E,E)-1,4-diphenyl-1,3-butadiene, while the broader range in the crude sample indicates the presence of impurities or possibly a mixture of isomers.
Explanation
The melting point of a compound is a crucial physical property used to assess its purity and identity. The literature melting point of (E,E)-1,4-diphenyl-1,3-butadiene is reported as 145–148 °C. In your experiment, the crude product had a melting point range of 139.0–148.7 °C, while the recrystallized product had a narrower and higher melting point range of 145.1–148.4 °C.
The broader and lower-range melting point of the crude product suggests the presence of impurities or a mixture of stereoisomers. Impurities disrupt the orderly lattice structure of a crystalline solid, causing the compound to melt over a wider range and at a lower temperature than the pure substance. The (Z,E)- or (Z,Z)-isomers, if present, could also lower and broaden the melting range due to different packing efficiencies.
In contrast, the melting point of the recrystallized product closely matches the literature value for the pure (E,E)-isomer and has a narrow range (145.1–148.4 °C), which is a strong indicator of increased purity and likely identity as (E,E)-1,4-diphenyl-1,3-butadiene. Recrystallization is a purification technique that removes impurities and separates isomers based on solubility differences. The fact that the recrystallized sample’s melting point aligns with the expected value strongly supports that the product is the desired (E,E)-isomer.
In summary, the melting point data confirms that the crude sample likely contained impurities or a mixture, but the recrystallized product is consistent with pure (E,E)-1,4-diphenyl-1,3-butadiene. The improved melting point after purification illustrates the success of recrystallization in isolating the correct isomer with high purity.
