For pinene, indicate which isoform (alpha/beta) is present. Two NMR spectra were
ID: 1016975 • Letter: F
Question
For pinene, indicate which isoform (alpha/beta) is present. Two NMR spectra were suggested for aid in this question. The calculated optical rotation was found to be -20.299 (with some unknown contamination from limonene present). This question is driving me nuts! I have no idea how to figure it out.
Pinene Oil H1-NMR in CDCI3 1.68 1.62 1.56 1.50 1.44 1.38 1.32 1.26 f1 (ppm) 2.55 2.45 2.35 2.252.15 2.05 1.95 f1 (ppm) 0.36 1.00 2.22 3.30 0.35 0.56 7.0 6.0 4.0 3.5 f1 (ppm) 6.5 5.5 5.0 4.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0Explanation / Answer
The optical rotation of -20.299 degree is more close to beta-pinene (-19 to -23 degree reported value)
Alpha-pinene would show one olefinic proton in the region 5.0-6. ppm region as triplet. On the other hand we would have a singlet for two protons in alkenic region 5-6 ppm for beta-pinene.
So in the above case we have beta-pinene and not alpha-pinene.
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