sacct.csus.edu NMR Analysis Practice Chemistry 125, Spring 2018 This homework as
ID: 578000 • Letter: S
Question
sacct.csus.edu NMR Analysis Practice Chemistry 125, Spring 2018 This homework assignment will give you an introduction to the art of using both 1D and 2D NMR analysis to assign the peaks in basic 'H and 13C spectroscopy. On the next few pages you are given the basic proton and carbon NMR spectra for -terpinene (structure shown below). In addition, you are given the COSY, HMQC, and HMBC for this molecule Hc Hd He Ha Hg H Your job is to analyze all of the spectra in order to give the exact ppm assignments for every proton and carbon atom in this molecule. (Please use the lettered proton assignments and the numbered carbon assignments given in the structures above.) You must include a justification for your assignments as well. Give the assignments (in ppm) and the source of the NMR data which you are using to justify your choice in addition to the reasornExplanation / Answer
There are 5 different types of proton are present in alpha terpinene compound. The protons of c and d are one group, e and f are another one group around same chemical environment.
The 2 CH3 groups will resonate at at 1.06 ppm as two singlets.
The next CH proton will resonate around 2.52 ppm as multiplet. According to n+1 rule there are 7 H’s present nearby that proton. Hence multiplet occurs.
The third CH2 group proton will give signal at 2.15 ppm as pentet. Nearby one CH3 and CH group present. Hence pentet.
The CH3 group will give signal at 1.82 ppm as doublet of singlet as adjacent two different protons.
The =CH protons will resonate at 5.68 ppm as the electronegativity of pi bonds make the proton resonation away from aliphatic region. The signal at 5.68 – 5.8 ppm is about singlet of doublet and a quartret.
There are 9 different types of carbon environments are present as shown in the model. All the signals are singlet only as the spectra will be proton decoupled.
Both C1 carbon of CH3 group will resonate at 21.9 ppm.
The C2 carbon will give signal at 34.5 ppm which is typical aliphatic CH region.
The C3 carbon give signal at 142.7 ppm adjacent to electronegative pi bond.
The C4 and C5 carbon at 26.1 and 28.8 ppm which is typical aliphatic CH2 region.
The C6 carbon will resonate at 133.1 ppm which is nearby the pi bond.
The C7 carbon CH3 group will give signal at 24.8 ppm for typical aliphatic CH3 region.
The C8 and C9 carbon at around 120.1 ppm and 116.5 ppm for aromatic carbon attached with hydrogen. The two aromatic CH group will give different signals.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.