The following pages present 5 structure problems where you are provided with a m
ID: 1054971 • Letter: T
Question
The following pages present 5 structure problems where you are provided with a mass spectrum, IR spectrum, C NMR spectrum, and 'H NMR spectrum for an unknown compound. Based on the information from the four spectra, you are to propose a structure for the unknown. To receive the 10 points allotted for this assignment, solve any two of the five problems. Clearly indicate which two you would like me to grade. Be sure to show all of your work and reasoning to obtain full credit. Do not iust provide a structure. I would encourage you to attempt all five problems for practice, but only two will be graded. There is no extra credit for turning in solutions to more than two problems, but trying to solve all problems will, of course, help your understanding.Explanation / Answer
Interpretation of spectra
#2
IR
2850-2950 cm-1 for aliphatic C-H stretch
2700 cm-1 and 2850 cm-1 peaks for aldehyde -CHO
1720 cm-1 for C=O stretch
1H NMR
1.0 ppm (doublet, 6H) for two CH3's next to CH
2.2 ppm (multiplet, 1H) for CH between two CH3's and a CH2
2.3 ppm (doublet, 2H) for CH2 between CH and CHO
13C NMR
22 ppm for CH3 carbons
23 ppm for CH carbon
52 ppm for CH2 carbon
202 ppm for C=O carbon
Mass
M+ 86
loss of CH3 forms m/z 71
Loss of CHO forms m/z 57
Structure of compound
(CH3)2CHCH2CHO
#4
IR
2850-2950 cm-1 for aliphatic C-H stretch
1H NMR
1.0 ppm (triplet, 3H) for CH3 next to CH2
2.0 ppm (sextet, 2H) for CH2 between CH3 and CH2
3.5 ppm (triplet, 2H) for CH2 between CH2 and Br
13C NMR
12 ppm for CH3 carbon
25 ppm for CH2 carbon between CH3 and CH2
35 ppm for CH2 carbon between CH2 and Br
Mass
M+ 122
peaks m/z 122 and m/z 124 in the ratio 1 : 1 suggest Br-79 and Br-81 present
loss of Br gives m/z 43
Structure of the compound
CH3CH2CH2Br
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