Chemistry 4000 Midterm Exam
February 15 2008
Answer all of the questions in the exam booklet provided. Time permitted for this exam
is 50 minutes. Total marks = 60.
Part 1 (15 marks)
Match the IR spectra A through E to the following compounds:
3-hydroxy-2-butanone, ethylacetate, 1,4-dioxane, 1-methoxy-2-propanone, and butanoic
acid
Justify your answer with diagnostic IR frequencies.
A)
B)
C)
D)
E)
Part II (15 Marks)
The following mass spectra are of three isomers of pentanol. Determine which spectrum
corresponds to each isomer, use fragmentation arguments to support your answer.
Part III (10 Marks)
The following mass spectrum is of ethylbutyrate (also called ethylbutanoate). Draw the
fragmentation pattern, indicate all the important fragments essential to assigning its
structure.
14.0
15.0
18.0
26.0
27.0
28.0
29.0
30.0
31.0
38.0
39.0
1
5
2
4
42
9
65
1
2
1
12
40.0
41.0
42.0
43.0
44.0
45.0
55.0
57.0
60.0
61.0
70.0
2
29
12
99
3
18
3
1
21
9
8
71.0
72.0
73.0
88.0
89.0
101.0
116.0
100
4
18
51
14
7
4
Part IV (4 marks each)
Answer 5 of the following 7 questions. Use equations and diagrams to aid your answer
where ever required.
1)
Why does the IR stretching frequency of C-X decrease in the series, X= F, Cl, Br,
F.
2)
For the mass spectrum of 2-methyl-2-hexanol predict the order of relative
intensities of the following peaks: m/z = 101, 87 and 73 and explain your choice.
3)
Explain why the C=O stretching frequency is larger for an acid anhydride than for
an ester.
4)
Explain the absence of a peak at m/z =118 when comparing the spectrum of omethyl-phenol and m-methyl phenol.
5)
Explain why the C=O stretching frequency of benzamide is lower and that of Nphenyl formamide is higher than formamide.
6)
The mass spectrum of isopropyl benzene has an important peak at 105, while that
of n-propylbenzene has two important peaks 91 and 92. Show the fragmentation
pattern of each molecule and explain the reason for the difference in the spectra..
7)
Why is the C=O stretching frequency of o-hydroxybenzaldehyde much reduced
compared to that of p-hydroxybenzaldehyde.