There are 25 peaks (28 if you count the solvent) in the 13 C NMR spectrum of tri
ID: 1024967 • Letter: T
Question
There are 25 peaks (28 if you count the solvent) in the 13C NMR spectrum of trifluoroacetylguaiazulene**, even though one might expect 16 peaks based on the number of chemically distinct carbons. What accounts for the extra peaks? (and just in case you’re wondering: NO, the extra peaks are not due to impurities) List the chemical shift of all 16 carbons.
Figure 2. 1C NMR spectrum (150 MHz, CDCl3) of trifluoroacetylguaiazulene MKI-63 13C 4000 3500 3000 2500 2000 1500 1000 500 70 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 f1 (ppm)Explanation / Answer
These peaks are not due to impurities. Presence fluorine atom splits the peak in 13C spectrum. The reason is fluorine nucleus has positive I value which is 1/2. Due to presence of three chemically equivalent three fluorine atoms each carbon near to fluorine (up to 3 bonds) splits into quadret.
Number of Peaks = 2nI + 1
n= no. of nucleus
I= spin magnetic moment value
In our case number of peaks = (2x3x1/2)+1 = 4 (quadret)
In your spectrum, there are 3 quadrets
(175.30,175.08,174.86,174.65) due to carbonyl carbon
(140.74,140.71,140.69,140.66) due to aromatic carbon
(118.85,117.73,116.91,114.98) due to CF3 carbon
Also J value indicates distance from the fluorine atom.
So you got 25 peaks. 13+4+4+4
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