1h Nmr Questions
July 29th, 2011 | Author: admin
William asks…
How would the 1H NMR spectrum of 1,3-dibenzoylpropane differ from that of the product?
How would the 1H NMR spectrum of 1,3-dibenzoylpropane differ from that of the product, trans-1,2-dibenzoylcyclopropane? would the chemical shifts of the protons alpha and beta to the carbonyl groups be appreciably different? explain.
admin answers:
PhC(=O)-CH2CH2CH2-C(=O)Ph
versus PhCO-CH-(~CH2~)-CH-COPh
first the amount of protons are very different in the structures… Lets count AROMATIC versus aliphatic… Top structure is 10 : 6 bottom structure is 10 : 4
for the cyclopropane there are TWO isomers… That is CIS or TRANS, so that you can have two DIFFERENT sets of resonances.
Both have symmetry… So the top structure has alpha CH2 triplet d2.5 with 4H’s and beta CH2 pentet d1.8 with 2H’s
cyclopropane…. CH doublet doublet d2 or so with 2H and CH2 will be a mess:) likely multiplets at d1.5 1H each.
Mark asks…
A triplet and quartet pattern in 1H NMR often indicates the presence of what alkyl group?
A triplet and quartet pattern in 1H NMR often indicates the presence of what alkyl group?
This is covering spectroscopy, I am really struggling Please help if you can, and be as detailed as possible. Thank you.
admin answers:
Ethyl most likely
n+1 rule means that you have CH2 and CH3 bond to each other
Betty asks…
number of proton signals of 1H NMR spectrum for tetrahydrofuran and multiplicity of downfield signal and upfie?
The structure of THF (tetrahydrofuran) is given below.
A) How many proton signals will appear on the 1H NMR spectrum?
B) What will the multiplicity of the downfield signal of the 1H NMR spectrum be?
C) What will the multiplicity of the upfield signal of the 1H NMR spectrum be?
D) How many C-13 signals will appear on the 13C NMR spectrum?
admin answers:
Sounds like someone chose the wrong compound to give students as homework!
There are two groups of chemically equivalent protons, of course. One at 3.7ppm and one at 1.8ppm, but because there is no free rotation around any of the C-C or C-O bonds, they are not magnetically equivalent. In the first order approximation (vicinal couplings only), the group at 3.7 ppm can have up to 16 peaks and the group at 1.8 ppm can have up to 64 peaks (in reality there’s probably half of that due to symmetry, but if you count four-bond couplings, which can easily be over 1Hz here, then there’s a lot more peaks to find). Everybody’s favorite public database AIST SDBS doesn’t have a well-resolved spectrum of THF, but in their 2-methyl THF, the 1.8ppm multiplet has 52 visible peaks!
Only (D) is a simple question 
two signals, one at 68ppm, one at 26ppm.
Linda asks…
A large doublet and a small septet pattern in 1H NMR is usually indicative of what alkyl group? ?
A large doublet and a small septet pattern in 1H NMR is usually indicative of what alkyl group?
I am having a little trouble with this question in my Organic Chemistry 1 course. This is covering spectroscopy, I am really struggling Please help if you can, and be as detailed as possible. Thank you.
admin answers:
The N + 1 adjacency rule applies here. A double means there is 1 H next to it. N + 1 = 1 + 1 = doublet.
Septet means 7 = N + 1; N = 6. How can you have 6 H’s and 1 H?
CH(CH3)2
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