Spectroscopy Problems Part 1

Spectroscopy Problems

Part 1

Introduction to IR and Mass Spectroscopy

Dallas K. Bates Michigan Technological University

Part 1: Introduction to IR and MS © Dallas K. Bates 2006 1

This series of problems has undergone several iterations over the years. I would like to thank former students of CH404 and CH4412 for their interest in spectroscopy and their helpful comments on spectral data presentation and interpretation. The changes I have made to drafts over time were driven by their input and interest in solving spectroscopy problems. There is no greater motivator for an instructor than a classroom full of active, inquisitive minds. I would also like to thank my graduate students who have discovered many anomalous reactions that have become fertile ground for new spectroscopy problems. I would especially like to thank Geetha Boreddy, Anil Ekkati, and Parag Jog who recorded many of the original spectra reproduced here. They have always been so ready to help out with any task I suggest and so gracious and generous with their time that it is impossible for me to adequately express my thanks. If you have any questions or comments about the material in this text, feel free to contact me at [email protected]


Table of Contents Problem 1 ……………Molecular Formula/MW………………….page 2 Problem 2 ……………Molecular Formula/MW………..……….page 3

Hints for solving IR- and MS –based spectroscopy problems…….…………………………………………………………………page 5

Guidelines for preparing your Bluebook of Useful Spectroscopic Information………………………………..………..page 7

IR spectra only

Problem 3 …………………………………………………………………….page 8 Problem 4 …………………………………………………………………….page 12 Problem 5 …………………………………………………………………….page 16

Mass spectra only

Problem 6 ……………Exact Mass/Isotope ratios…………….page 19 Problem 7 ……………predicting fragmentation…….……….page 21 Problem 8 ……………predicting fragmentation……….…….page 22 Problem 9 ……………predicting fragmentation…….……….page 23 Problem 10 ……………………………………..……..……….…………page 24 Problem 11 ……………………………………..….……..………………page 25 Problem 12 ……………………………………………………….…….….page 26 Problem 13 …………………………………………….………….……….page 27 Problem 14 ……………………………………………………….…………page 28 Problem 15 ……………………………………………………….…………page 29 Problem 16 …………………………………………………….……………page 30 Problem 17 ………………………………………………….………………page 31

IR + MS problems

Problem 18 ………………………………………………….………………page 32 Problem 19 ……………………………………………….…………………page 33 Problem 20 ……………………………………………….…………………page 37 Problem 21 ……………………………………………….…………………page 38 Problem 22 …………………………………………….……………………page 39 Problem 23 …………………………………………….……………………page 40 Problem 24 …………………………………………….……………………page 41 Problem 25 …………………………………………….……………………page 43 Problem 26…….…………… Using on-line IR databases page 45 Problem 27 …………… IR+MS+1H NMR problem …………page 46


Problem 1 An article in the December 28, 2001 issue of the Journal of Organic Chemistry describes the isolation of a compound the authors named nomofungin by a bioassay-directed isolation procedure. The compound shows biological activity (microfilament disruption) analogous to Taxol, a drug used in cancer treatment. It was isolated from a fungus collected on the campus of the University of Hawaii at Manoa. As the culture was processed it stopped producing this compound and subsequent attempts to find more of the native fungus failed (hence nomofungin). (a) What is the molecular formula of nomofungin? ______________________________ (b) What is the molecular weight of nomofungin (round to ONE decimal place)? ____________ (c) At what nominal m/z value would you expect to see the molecular

ion peak of nomofungin in a low resolution mass spectrum? ___________

N

NO

NO

O

MeH

NOMOFUNGIN


Problem 2 An article in the July 14, 2000 issue of the Journal of Organic Chemistry describes the isolation of compound 2 from human urine, its characterization by UV, 1H NMR, 13C NMR, low resolution mass spec (LRMS) with FAB volatilization of the sample (its mp is > 400 oC), HRMS, combustion microanalysis, and formal total synthesis. (a) What is the molecular formula of 2? ______________________________ (b) What is the molecular weight of 2 (to one decimal place)? _____________ (c) At what m/z value would you expect to see the molecular ion peak

of 2? __________

NS

N

HO

HO

H

COOH

H

COOH

2


Some hints for solving problems

IR Problems

Initial analysis of an IR spectrum requires only a couple of minutes looking for the presence or absence diagnostic peaks for common

functional groups. In many cases what is not seen in the spectrum is as important as what is seen. For example, it is

possible to ascertain very quickly if a carbonyl group present or not present in an unknown sample. If present, with a little

additional work it is usually possible to determine what type of carbonyl (amide, acid chloride, ester, ketone, conjugated or non-

conjugated, etc.) the unknown sample contains.

IR spectra are usually used in conjunction with other spectral data. The main use is to confirm suspicions raised by NMR or mass spec data about functional groups present or absent. For example, coupling

constants and chemical shifts in a 1H NMR may point to the presence of a trans-alkene. Looking for peaks in the IR to differentiate cis- from

trans- isomers would be useful to reinforce this initial hypothesis about the presence and stereochemistry of the double bond.

Figure 1

IR spectrum of acetone. (note large C=O stretch at 1715 cm-1 and absence of any signals >3000 cm-1 (no OH, NH, alkene, or aryl CH’s)


Mass Spectroscopy Problems

1. List M+ and the m/z values for all major fragment ions.

2. To help identify the M+, look for isotope clusters and apply the nitrogen rule (is M+ even or odd?).

3. Determine the masses of the fragments lost to produce the major ions. What are you looking for are masses that equate with common fragments lost, such as M-15 for the loss of methyl, M-35 for loss of Cl, etc.

Figure 2

Part 1: Introduction to IR and MS © Dallas K. Bates 2006 page 7

“Bluebook of Useful Spectroscopic Information”

You can purchase a bluebook from the bookstore and fill it with information you can use as a reference for solving problems in

CH4412. You may also use it for all graded work (quizzes, tests, etc.). You may include material from any source, but you must hand-write

any information in your bluebook.

I would suggest you prepare four sections in your blue book dedicated to IR, MS, 1H NMR, and 13C NMR, respectively. It is a temptation to pack into your bluebook every detail about diagnostic spectroscopic information you can lay your hands on. However, I caution you to be

selective. The more information, the longer it takes to find the specific information you need when you need it. If you have any questions

about organizing material or what material would be most useful for your bluebook, just ask me.

Reiterating: ALL information in your bluebook must be hand-written by you.


Problem 3 Match the five IR spectra shown with the appropriate compound below. Indicate your answer by placing the spectrum number in the appropriate space. Note: spectra 1-3 are courtesy of Geetha Boreddy.

IR Spectrum # ______

benzonitrile


cumene


butanamine


2,4-dimethylaniline


N,N-diethylaniline

CN

CCH3

CH3

H

NH2

NCH2CH3

CH2CH3

NH2

CH3 CH3


Problem 3 Spectrum 1 (3354, 3290, 1611, 1477, 1330, 1176, 827, 688 cm-1)

Problem 3 Spectrum 2 (3065, 2229, 1598, 1491, 1447, 1288, 760, 688 cm-1)


Problem 3 Spectrum 3 (some major peaks: 2961, 1451, 1383, 760, 698 cm-1)

Problem 3 Spectrum 4 (some major peaks: 3473, 3383, 1622, 1477, 760 cm-1)

Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 5, 2004)


Problem 3 Spectrum 5 (2970, 1597, 1506, 1265, 1199, 744, 692 cm-1)


Problem 4 Seven IR spectra are shown below and on the following pages. Based on functional group information obtained from these spectra, answer the following questions by supplying the appropriate compound number (a compound may be used more than once or not at all; some questions may have more than one correct answer).

(i) Which compound contains an aromatic ring? (ii) Which compound would be reduced by NaBH4 (in

EtOH/NaOH)? (iii) Which could be a reaction product from a NaBH4

reduction? (iv) Which is 2-methylpropanonitrile? (v) Which is a primary (1o) amine?

Problem 4 Compound 1 (IR summary: 3348, 2960, 1426, 1368, 1164, 1139,

1116, 1067, 1017, 921, 827, 649 cm-1)



Problem 4 Compound 2 (some major absorptions: 2960, 1716, 1426, 1407, 1367, 1171, 594 cm-1)

Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 5, 2004) Problem 4 Compound 3 (some major absorptions: 3369, 3293, 2960, 2928,

1606, 1465, 1379, 837 cm-1)



Problem 4 Compound 4 (some major absorptions: 2928, 2853, 1460, 1257, 1039, 1016, 904, 852 cm-1)

Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 5, 2004) Problem 4 Compound 5 (some major peaks: 2986, 2246, 1476, 1460, 1392,

1372, 1323, 1173, 1106, 934, 916, 751, 545 cm-1)



Problem 4 Compound 6 (IR summary: 3046, 3035, 1481, 1430, 730, 700 cm-1)

Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 9, 2004) Problem 4 Compound 7 (IR summary: 3077, 2970, 1651, 1466, 887 cm-1)



Problem 5 IR spectra (labeled A, B, C, and D) for four isomers (C5H10) appear on the next several pages. These compounds are 1-pentene, cis-2-pentene, trans-2-pentene, and 2-methyl-1-butene. Complete the Table provided below – match each compound to the appropriate spectrum and list the peaks that are useful for the assignments.

Table

Spectrum Compound Diagnostic bands (cm-1) A

B

C

D

Note: the intensity of a band in an IR spectrum is proportional to the change in dipole moment during the molecular vibration. Consequently, some bands in nearly symmetrical compounds are quite weak. For example, the C≡C stretch in 2-butyne, which is symmetrical around the triple bond, does not appear in the spectrum; in 2-pentyne, the band is present but weak.


Spectrum A

3079.8

2962.1

2929.3

2875.3

2844.5

1643.1

1457.9

991.2

910.2

20

30

40

50

60

70

80

90

100

4500 4250 4000 3750 3500 3250 3000 2750 2500 2250 2000 1750 1500 1250 1000 750 500 250

FTIRNEAT

ALL RIGHTS RESERVED© Sigma-Aldrich Co.

% T

ran

sm

itta

nce

Wavenumbers (cm-1)

Spectrum B

3016.1

2966.0

2935.1

2877.3

1658.5

1456.0

1403.9

1373.11305.6

933.4

696.2

30

40

50

60

70

80

90

100

4500 4250 4000 3750 3500 3250 3000 2750 2500 2250 2000 1750 1500 1250 1000 750 500 250

FTIRNEAT


% T

ran

sm

itta

nce

Wavenumbers (cm-1)


Spectrum C

Spectrum D

3075.9

2969.8

2937.1

2917.82881.1

2854.1 1650.8

1454.1

1375.0

887.1

20

30

40

50

60

70

80

90

100

4500 4250 4000 3750 3500 3250 3000 2750 2500 2250 2000 1750 1500 1250 1000 750 500 250

FTIRNEAT


% T

ransm

itta

nce

Wavenumbers (cm-1)

3023.8

2964.0

2921.6

2875.32856.1

1454.1

1440.6

1378.9

964.2

943.0

20

30

40

50

60

70

80

90

100

4500 4250 4000 3750 3500 3250 3000 2750 2500 2250 2000 1750 1500 1250 1000 750 500 250

FTIRNEAT


% T

ran

sm

itta

nce

Wavenumbers (cm-1)


Problem 6 Isotope peaks in LREI mass spectra can sometimes provide valuable information about the elemental composition of a compound. There are many computer programs available (some are available on the web as freeware) that will calculate expected ratio of P/P+1/P+2 (where P = a peak height) based on the elements present in the sample molecule and the isotopic abundances for those elements.

The Table on the next page (from Spectrometric Identification of Organic Compounds, 4th edition, p. 46) lists possible formulae for an m/z 130 peak (P) in an EI mass spectrum. Also listed are the calculated P+1 and P+2 values (for compounds containing C, H, N, and O). The formulae appearing in this Table may be molecular ions or fragment ions, all having a nominal mass of 130. For example, note that the second item in the list is C3H4N3O3; we know from the Nitrogen Rule that this must be a fragment ion, not a molecular ion. Why? Because the Nitrogen Rule states that a molecular ion for a molecular formula containing an odd number of nitrogen atoms must be odd. Since 130 is an even number, this molecular formula can not represent a molecular ion – it must represent a fragment ion.

Two mass spectra are shown below. One is a MS of quinoxaline and the other is for phenylpropargylaldehyde (both nominal MW = 130). Based on the M/M+1/M+2 ratios in the respective mass spectra, determine the molecular formula for phenylpropargylaldehyde and quinoxaline. Then, based on your formula, determine the HDI of each compound.

Phenylpropargylaldehyde Quinoxaline 132 0.7 132 0.4 131 9.9 131 9.6 130 100 130 100 129 93.0 129 2.0


Problem 6. Predicted P+1: P+2 ratios for an m/z 130 peak.

Nominal Mass = 130

P+1* P+2* Exact Mass

C3H2N2O4 4.19 0.87 130.0014 C3H4N3O3 4.57 0.69 130.0253 C3H6N4O2 4.94 0.50 130.0491 C4H4NO4 4.92 0.90 130.0140 C4H6N2O3 5.30 0.72 130.0379 C4H8N3O2 5.67 0.54 130.0617 C4H10N4O 6.05 0.36 130.0856 C5H6O4 5.66 0.93 130.0266

C5H8NO3 6.03 0.75 130.0504 C5H10N2O2 6.40 0.58 130.0743 C5H12N3O 6.78 0.40 130.0981 C5H14N4 7.15 0.22 130.1220 C6H10O3 6.76 0.79 130.0630

C6H12NO2 7.14 0.62 130.0868 C6H14N2O 7.51 0.45 130.1107 C6H16N3 7.88 0.27 130.1346 C6N3O 7.67 0.46 130.0042 C6H2N4 8.04 0.29 130.0280 C7H14O2 7.87 0.67 130.0994 C7H16NO 8.24 0.50 130.1233 C7NO2 8.02 0.68 130.9929

C7H18N2 8.62 0.33 130.1471 C7H2N2O 8.40 0.51 130.0167 C7H4N3 8.77 0.34 130.0406 C8H18O 8.97 0.56 130.1358 C8H2O2 8.75 0.74 130.0054 C8H4NO 9.13 0.57 130.0293 C8H6N2 9.50 0.40 130.0532 C9H6O 9.86 0.63 130.0419 C9H8N 10.23 0.47 130.0657 C10H10 10.97 0.54 130.0783

* Value when P has been normalized (scaled) to 100.


Problem 7 Draw the structures of two fragments expected to be produced in the LREIMS of compound 1.

Notes: LREIMS = Low Resolution Electron Impact Mass Spectrum Major fragments that appear in EIMS are often produced by

cleavage of easily broken bonds in the molecule. One easy way to identify these easily broken bonds is to locate bonds that will form a stable carbocation (the other species from the bond cleavage will be a free radical) when they are broken.

Recall from sophomore organic chemistry that benzyl and allyl

carbocations are very stable, followed by tertiary carbocations (3o), secondary (2o), and the not so stable primary (1o).

Benzyl and allyl carbocations derive their stability from pi

electron delocation (resonance-stabilization). Some other common resonance-stabilized cations are acylium (a) and the ions (b) and (c) [oxonium and iminium ions, respectively].

Most stable Least stable

CH2

CH2

CH3

O

N

O

N

O O (a)

(b)

(c)

CH3

O1


Problem 8 Predict peaks expected in the LREIMS of benzyl acetate. List peaks in order of decreasing m/z: (random number of spaces provided) _____ ____ ____ ____ ____ ____ ____ ____ ____


Cl

CH3

O

Problem 9 Predict the LREIMS of 4-chloroacetophenone (the structure is shown in the box below). List peaks in order of decreasing m/z.


Problem 10

(A) Identify the m/z values for the base peak and molecular ion (M+) in the mass spectrum shown in Figure 1.

Figure 1

(B) Suggest a structure for the compound whose mass spectrum (LRMS) is shown in Figure 2. Also suggest a structure for m/z 77 and for the fragment lost from the M+ to form m/z 77.

Figure 2


Problem 11

(A) Identify the m/z values for the base peak and molecular ion (M+) in the mass spectrum shown

(B) Suggest a structure for the compound producing this

spectrum. Also suggest a structure for m/z 91 and for the fragment lost from the M+ to form m/z 91.


Problem 12 Two LREIMS are shown below. Other than carbon and hydrogen atoms, each compound contains one oxygen atoms.

MS A m/z (rel abund): 50(12), 51(22), 77(52), 105(100), 140(4), 142(1.3)

MS B 43 (14), 75(17), 111(42/113(13.7), 139(100)/141(31.7), 154(26.7)/ 156(8.8)

Source: www.aist.go.jp/RIODB/SDBS (National Institute of Advanced Industrial Science and Technology, January 18, 2006).


Problem 13 The compound with EIMS shown below contains only C, H, and O. Identify the molecular ion and the base peak as well as any characteristic isotope clusters. Prepare a table of major fragment m/z values and the mass lost to form these fragments. Use these data to formulate a structure for this compound.


Problem 14 The compound with EIMS shown below contains only C, H, O and chlorine. Identify the molecular ion and the base peak as well as any characteristic isotope clusters. Prepare a table of major fragment m/z values and the mass lost to form these fragments. Use these data to formulate a structure for this compound.


Problem 15 The compound with EIMS shown below contains only C, H, and S. Identify the molecular ion and the base peak as well as any characteristic isotope clusters. Prepare a table of major fragment m/z values and the mass lost to form these fragments. Use these data to formulate a structure for this compound.


Problem 16 In addition to the element suggested by the molecular isotope cluster (out past m/z 220), the compound with EIMS shown below contains C, H, and O. Identify the molecular ion and the base peak. Prepare a table of major fragment m/z values and the mass lost to form these fragments. Use these data to formulate a structure for this compound.


Problem 17 The compound with EIMS shown below contains C, H, O and chlorine (C9H11ClO). Identify the molecular ion and the base peak. Prepare a table of major fragment m/z values and the mass lost to form these fragments. Use these data to formulate a structure for this compound.


Problem 18

Suggest a structure for compound 1 – whose mass spectra (LREIMS) are provided. Amongst the atoms present are 9 carbon atoms and 1 oxygen atom. IR (KBr):1684 cm-1; LREIMS [m/z (rel int): (shown on spectrum)

Compound 1 (139(100)

111(39)

50(11) 75(23) 141(32)

113(12) 168(16.5) 170(5.4)


Problem 19 IR and mass spectra for three compounds (C9H10O) whose structures are shown below are given on the following pages. Answer the three questions below about the structures and spectra.

(A) For the three structures shown, predict differences expected to be observed in the IR spectra.

(B) For each of the three structures shown, predict the structure and m/z values for major fragments. It would be useful to make a table containing the structures and their m/z values.

(C) Examine the IR spectra for the three compounds. What initial conclusions about which structure corresponds to each spectrum can you make?

(D) Examine each mass spectrum provided. Based on your table of expected fragments for each structure, assign a mass spectrum to each structure. Do these assignments agree with the preliminary conclusions reached from examining the IR spectra?

The spectra for this problem are from the NIST database.

CH3

O

H

O

O

X Y Z


Problem 19 Compound 1 IR spectrum (gas phase – major peaks: 1705, 1218 cm-1)

Mass spectrum (major peaks: m/z 134, 105, 77, 51)


Problem 19 Compound 2 IR spectrum (gas phase– some major peaks: 3078, 3038, 2966, 2930, 1730 cm-1)

Mass spectrum (major peaks: m/z 134, 91, 65, 63, 51, 43, 39)


Problem 19 Compound 3 IR spectrum (gas phase – major peaks: 2808, 2710, 1744 cm-1)

Mass spectrum (major peaks: m/z 134, 105, 91, 79, 77, 51, 39)


Problem 20 The IR (liquid film) and mass spectrum (LREI) of a benzoic acid derivative prepared as an intermediate in a multi-step chemical synthesis are shown below. Place your answers to the following four questions in the appropriate space on the attached sheet.

(A) Suggest a structure consistent with these data. (B) Assign the absorption at 1791 cm-1 in the IR spectrum. (C) What do the peaks at m/z 170/168 indicate? (D) Assign a structure to the peaks at m/z 133 and 105.

IR summary: 1791, 1467, 1186, 851, 774, 754, 711 cm-1.

MS summary [m/z (relative intensity)]: 170 (1.13) 168 (3.91) 133 (100) 105 (60) Spectra courtesy of Geetha Boreddy


Problem 21 Based upon the IR and mass spectral data shown below, match spectra X, Y, Z to compounds A, B, and C.


Problem 22 The IR (film) and mass spectrum (LREI) of an unknown compound are shown below. Note: An apparent contaminant shows peaks at 3642 and 3549 cm-1 (what functional group accounts for this?).

(A) Suggest a structure consistent with these data. (B) Identify the functional group responsible for the absorptions

at 2246, 1392 and 1372 cm-1. (C) Suggest structures for the M-1, M-15 and M-27 peaks.

IR summary: 2986, 2246, 1460, 1392, 1372, 1323, 1173, 1106, 934, 916 cm-1)

Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 9, 2004) MS summary: m/z 69, 68 (M-1), 54, 42.



Problem 23 The IR (KBr pellet) and mass spectrum (LREI) of an unknown compound are shown below.

(A) Suggest a structure for the compound. (B) Propose a mechanism for formation of the m/z 44 and

m/z 59 peaks by cleavages in the molecular ion. IR summary: 3366, 3184, 2962, 1662, 1634, 1430, 1418, 1379, 1344, 1313, 1263,

1145, 713, 666 cm-1

Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 12, 2004) MS peak listing:

87 2 86 3 72 19 59 100 44 66 43 32 42 7 41 53 39 11 29 26 27 26



Problem 24 The following IR and mass spectra are for two isomeric compounds (compounds A and B). The mass spectra are quite different, but they exhibit similar IR spectra. Propose structures for compounds A and B. Compound A IR summary: (broad peak >3000 cm-1 = impurity, 3051, 2801, 2230, 1689, 1403, 1367, 1266, 833 cm-1.

Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 12, 2004) Mass spectrum line listing: 145 17 130 100 102 47 75 10 43 18 Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 12, 2004)


Problem 24 (Data for Compound B) IR summary: (broad peak >3000 cm-1 = impurity, 3072, 2955, 2924, 2224 (C≡N), 1689, 1220, 767 cm-1.

Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 12, 2004) Mass spectrum line listing: 145 4 105 100 77 59 51 21 50 7 Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 12, 2004)


Problem 25 The IR and mass spectra of two isomeric compounds (A and B) are shown below. Suggest a structure for each compound. Compound A

Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 12, 2004) Mass spectrum line listing: 142 6 141 2 140 20 105 100 77 11 51 6 39 4 Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 12, 2004)


Problem 25 (Data for compound B)

Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 12, 2004) Mass spectrum line listing 142 4 141 1 140 14 105 3 91 100 77 6 65 5 51 7 39 3 Source: SDBSWeb: http://www.aist.go.jp/RIODB/SDBS/ (February 12, 2004)


Problem 26 Using on-line Chemistry Databases In this exercise you will use the National Institute of Standards and Technology (NIST) on-line Chemistry WebBook and the SDBS Integrated Spectral Data Base System for Organic Compounds to find the MS and IR of an assigned organic compound, analyze the spectra to assign structures to the important fragments and functional groups to representative bands in the respective spectra. The NIST Chemistry WebBook contains thermochemical, heat of reaction data, and IR and MS data. The SDBS Integrated Spectral Data Base System for Organic Compounds contains IR, MS, 1H and 13C NMR spectra. The databases may be searched by name, chemical formula, CAS registry number, molecular weight, or user specified properties. The URLs are: http://webbook.nist.gov and http://www.aist.go.jp/RIODB/SDBS

Specific Assignment: Your assigned compound will be announced in class. A sample report is also posted on the CH4412 web page. Search for the IR and mass spectrum for your assigned compound. Report the following on a sheet of paper to be handed-in by the date specified on the bulletin board:

(A) The name and structure of the compound (and CAS registry number, if available).

(B) Mass spectrum, IR spectrum, or both depending upon availability in the database.

(C) Structures of fragment ions (mass spec) and functional group absorptions (IR).

This assignment will be handed in and graded as a quiz (10 points). NOTE: To print the MS and IR spectra for your compound, you need to select the “large spectrum image” (click on the icon just below the spectrum). You will also need to change the print orientation from portrait to landscape (in the print window click the properties button next to the printer name to get the appropriate text box). For the IR spectrum, you may need to choose “Reverse X” to present the spectrum in the standard presentation format having wave numbers (cm-1) decrease from left to right in the spectrum - this will make more sense when you look at a spectrum.


Problem 27

The attached IR, LRMS, and 1H NMR were obtained for a compound C12H16O. Propose a structure for the compound producing these spectra and assign signals to the structure.


Problem 27 (continued) 1H NMR spectrum


Problem 27 (continued) LREI Mass Spectrum

Documents

Spectroscopy Problems Part 1