# 9.E: Separation, Purification, & Identification of Organic Compounds (Exercises)

Exercise 9-1 Suppose you are standing on the end of a pier watching the waves and, between your position and a buoy $$200 \: \text{m}$$ straight out, you count 15 wave crests. Further, suppose a wave crest comes by every 15 seconds. Calculate $$\nu$$ in $$\text{Hz}$$, $$\lambda$$ in $$\text{m}$$, $$c$$ in $$\text{m sec}^{-1}$$, and $$\bar{\nu}$$ in $$\text{km}^{-1}$$.

Exercise 9-2 Blue light has $$\bar{\nu} = 20,800 \: \text{cm}^{-1}$$. Calculate $$\nu$$ in $$\text{Hz}$$ and $$\lambda$$ in $$\text{nm}$$.

Exercise 9-3 Calculate the energy in $$\text{kcal mol}^{-1}$$ that corresponds to the absorption of 1 einstein of light of $$589.3 \: \text{nm}$$ (sodium $$D$$ line) by sodium vapor. Explain how this absorption of light by sodium vapor may have chemical utility.

Exercise 9-4

a. Use Equations 9-1 and 9-2 to calculate the wavelength in $$\text{nm}$$ and energy in $$\text{kcal}$$ of an einstein of radiation of radio-frequency energy in the broadcast band having $$\nu = 1 \: \text{MHz}$$ (1 megahertz) $$= 10^6 \: \text{sec}^{-1}$$ and knowing that the velocity of light is approximately $$3 \times 10^8 \: \text{m sec}^{-1}$$.

b. In photoelectron spectroscopy, x-rays with energies of approximately $$1250 \: \text{eV}$$ are used ($$1 \: \text{eV}$$ (electron volt) $$\text{mol}^{-1} = 23.05 \: \text{kcal}$$). What would $$\lambda$$ (in $$\text{nm}$$) be for such x-rays?

Exercise 9-5 The microwave spectrum of pure trans-2-butenoic acid $$\left( \ce{CH_3CH=CHCO_2H} \right)$$ shows patterns exactly like those of Figure 9-8, which indicate the presence of two different conformations. What are these conformations, and why are there only two of them? (You may be helped by reviewing Section 6-5.)

Exercise 9-6 Use Equation 9-3 and any other pertinent data to predict which compound in each group would absorb in the infrared at the highest frequency for the changes in the stretching vibration of the specified bond. Give your reasoning.

a. $$\ce{R-Cl}$$, $$\ce{R-Br}$$, $$\ce{R-F}$$ (carbon-halogen)
b. $$\ce{CH_3-NH_2}$$, $$\ce{CH_2=NH}$$, $$\ce{HC \equiv N}$$ (carbon-nitrogen)

Exercise 9-7 Which compound in each group would have the most intense infrared absorption band corresponding to stretching vibrations of the bonds indicated? Give your reasoning.

a. $$\ce{(CH_3)_2C=O}$$, $$\ce{(CH_3)_2C=CH_2}$$ (multiple bond)
b. $$\ce{CH_3-CH_3}$$, $$\ce{CH_3-O-CH_3}$$ ($$\ce{C-C}$$ vs. $$\ce{C-O}$$)
c. $$\ce{CH_3C \equiv CH}$$, $$\ce{CH_3C \equiv CCH_3}$$ (multiple bond)
d. $$\ce{H-Cl}$$, $$\ce{Cl-Cl}$$

Exercise 9-8* How many vibrational modes are possible for (a) $$\ce{CS_2}$$ (linear), (b) $$\ce{BeCl_2}$$ (linear), and (c) $$\ce{SO_2}$$ (angular)? Show your reasoning.

Exercise 9-9* Suppose an infrared absorption occurs at $$3000 \: \text{cm}^{-1}$$. Calculate the corresponding frequency $$\nu$$ in $$\text{sec}^{-1}$$; $$\lambda$$ in $$\text{nm}$$, angstroms, and microns, and energy change in $$\text{kcal mol}^{-1}$$. Using Equation 4-2 and neglecting $$\Delta S$$, calculate the fraction of the molecules that would be in the ground state and in the first vibrational excited state (above ground state by $$3000 \: \text{cm}^{-1}$$) at $$298^\text{o} \text{K}$$.

Exercise 9-10 Use Table 9-2 to map the approximate positions and intensities expected for the characteristic infrared bands corresponding to the stretching vibrations of the various kinds of bonds in the following molecules:

a. 1,1,1-trideuteriopropanone (trideuterioacetone)

b. propyne

c. ethyl ethanoate (ethyl acetate)

d. propanenitrile (acrylonitrile)

e. 2-oxopropanoic acid (pyruvic acid)

f. ethanol (ethyl alcohol) (both as pure liquid and as a dilute solution in $$\ce{CCl_4}$$)

Exercise 9-11 The infrared spectra shown in Figure 9-14 are for compounds of formula $$\ce{C_3H_O}$$ and $$\ce{C_3H_6O_2}$$. Use the data in Table 9-2 and the molecular formulas to deduce a structure for each of these substances from its infrared spectrum. Indicate clearly which lines in the spectra you identify with the groups in your structures.

Figure 9-14: Infrared spectra for Exercise 9-11. Spectrum (a) corresponds to $$\ce{C_3H_6O}$$ and Spectrum (b) to $$\ce{C_3H_6O_2}$$.

Exercise 9-12* Classify the following molecules according to the general characteristics expected for their infrared and Raman spectra:

a. $$\ce{HC \equiv CH}$$
b. $$\ce{ICl}$$
c. $$\ce{CO}$$
d. $$\ce{CF_2=CH_2}$$ (double-bond stretch only)
e. $$\ce{(CH_3)_2C=CH_2}$$
f. $$\ce{CH_3CH=CHCH_3}$$

Exercise 9-13* Carbon dioxide gives two infrared absorption bands but only one Raman line. This Raman line corresponds to a different vibration than the infrared absorptions. Decide which vibrational modes are infrared active (i.e., make the molecule electrically unsymmetrical during at least part of the vibration) and which is Raman active (i.e., occurs so the molecule is electrically symmetrical at all times during the vibration, see Section 9-7A).

Exercise 9-14 List the kinds of electronic transitions that would be expected for azaethene (methyleneimine), $$\ce{CH_2=NH}$$, in order of increasing energy. Use the data in Table 9-3 to predict approximately the wavelengths at which the three lowest-energy transitions should occur.

Exercise 9-15 Calculate the percentage of the incident light that would be absorbed by an $$0.010 \: \text{M}$$ solution of 2-propanone (acetone) in cyclohexane contained in a quartz cell $$0.1 \: \text{cm}$$ long at $$280 \: \text{nm}$$ and at $$190 \: \text{nm}$$ (see footnote $$a$$ of Table 9-3).

Exercise 9-16 Explain why the absorption band at $$227.3 \: \text{nm}$$ for trimethylamine, $$\ce{(CH_3)_3N}$$, disappears in acid solution.

Exercise 9-17 A compound of formula $$\ce{C_4H_6O}$$ has two absorption bands in the ultraviolet: $$\lambda = 320 \: \text{nm}$$, $$\epsilon = 30$$ and $$\lambda = 218 \: \text{nm}$$, $$\epsilon = 18,000$$ in ethanol solution. Draw three possible structures that are consistent with this information.

Exercise 9-18 2,4-Pentadione exists in equilibrium with 4-hydroxy-3-penten-2-one:

The infrared spectrum of the liquid mixture shows a broad absorption band at $$3000$$-$$2700 \: \text{cm}^{-1}$$ and an intense absorption band at $$1613 \: \text{cm}^{-1}$$. In cyclohexane solution, the substances has $$\lambda_\text{max}$$ at $$272 \: \text{nm}$$ with $$\epsilon_\text{max} = 12,000$$.

a. What can you conclude from this data as to the magnitude of $$K$$, the equilibrium constant for the interconversion of the two forms?

b. What can you deduce from the fact that the absorption at $$272 \: \text{nm}$$ is much weaker in aqueous solution (pH 7) than it is in cyclohexane?

Exercise 9-19* The electronic absorption spectrum of 2-nitrobenzenol has $$\lambda_\text{max}$$ in $$0.1 \: \text{M} \: \ce{HCl}$$ at $$350 \: \text{nm}$$. In $$0.1 \: \text{M} \: \ce{NaOH}$$, the benzenol is largely converted to its anion, and $$\lambda_\text{max}$$ shifts to $$415 \: \text{nm}$$.

The ground-state resonance forms of 2-nitrobenzenol and its anion include

Explain how the relative importance of these resonance forms to the ground and excited states of 2-nitrobenzenol and its anion can account for the fact that the anion absorbs at longer wavelengths than does 2-nitrobenzenol. (Review Section 6-5B)

Exercise 9-20* A solution containing the two forms of the important coenzyme nicotinamide adenine dinucleotide (abbreviated $$\ce{NAD}^\oplus$$ and $$\ce{NADH}$$; see Section 15-6C for structures) has an absorbance in a $$1$$-$$\text{cm}$$ cell of 0.311 at $$340 \: \text{nm}$$ and 1.2 at $$260 \: \text{nm}$$. Both $$\ce{NAD}^\oplus$$ and $$\ce{NADH}$$ absorb at $$260 \: \text{nm}$$, but only $$\ce{NADH}$$ absorbs at $$340 \: \text{nm}$$. The molar extinction coefficients are

$\begin{array}{lll} \underline{\text{Compound}} & \underline{260 \: \text{nm}} & \underline{340 \: \text{nm}} \\ \ce{NAD}^\oplus & 18,000 & \sim 0 \\ \ce{NADH} & 15,000 & 6220 \end{array}$

Calculate the proportions of $$\ce{NAD}^\oplus$$ and $$\ce{NADH}$$ in the mixture.

Exercise 9-21 Use Figure 9-24 to map the nmr spectrum you would expect for $$\ce{^{13}CCl_3 \: ^1H}$$ in a field-sweep spectrometer in which the transmitter frequency is kept constant at $$30 \: \text{MHz}$$ and the magnetic field is swept from 0 to 30,000 gauss. Do the same for a frequency-sweep spectrometer when the magnetic field is kept constant at 10,000 gauss and the frequency is swept from $$0$$ to $$100 \: \text{MHz}$$. (For various reasons, practical spectrometers do not sweep over such wide ranges of field or frequency.)

Exercise 9-22* In nmr experiments, structural inferences sometimes are drawn from differences in resonance frequencies as small as $$1 \: \text{Hz}$$. What difference in energy in $$\text{kcal mol}^{-1}$$ does $$1 \: \text{Hz}$$ represent?

Exercise 9-23* The intensity of nmr signals normally increases markedly with decreasing temperature because more magnetic nuclei are in the $$+\frac{1}{2}$$ state. Calculate the equilibrium constant at $$-90^\text{o}$$ for the $$+\frac{1}{2}$$ and $$-\frac{1}{2}$$ states of $$\ce{^1H}$$ in a magnetic field of 42,300 gauss when the resonance frequency is $$180 \: \text{MHz}$$.

Exercise 9-24

a. Identify the protons with different chemical shifts in each of the structures shown. Use letter subscripts $$\ce{H}_A$$, $$\ce{H}_B$$, and so on, to designate nonequivalent protons. Use models if necessary.

(i) cis- and trans-2-butene
(iii) 1-chloro-2,2-dimethylbutane
(iv) 2-butanol
(v) trans-1,2-dibromocyclopropane

b.* Why does 3-methyl-2-butanol have three methyl resonances with different chemical shifts in its proton nmr spectrum?

c.* For the compounds in Part a designated those protons (if any) that are enantiotopic or diastereotopic.

Exercise 9-25 Use Equation 9-4 to calculate the chemical shift of the $$\ce{-CH_2}-$$ protons on

a. $$\ce{CH_2Cl_2}$$
b. $$\ce{ClCH_2OCH_3}$$
c. $$\ce{C_6H_5CH_2CO_2H}$$

Exercise 9-26 If the $$\ce{-NH_2}$$ protons of 2-aminoethanol, $$\ce{NH_2CH_2CH_2OH}$$, have a shift of $$1.1 \: \text{ppm}$$ and the $$\ce{-OH}$$ proton has a shift of $$3.2 \: \text{ppm}$$, what will be the observed average ($$\ce{-NH_2}$$, $$\ce{-OH}$$) proton shift if exchange is very fast?

Exercise 9-27 In reasonably concentrated solution in water, ethanoic acid (acetic acid) acts as a weak acid (less than $$1\%$$ dissociated). Ethanoic acid gives two proton nmr resonance lines at $$2$$ and $$11 \: \text{ppm}$$, relative to TMS, whereas water gives a line at $$5 \: \text{ppm}$$. Nonetheless, mixtures of ethanoic acid and water are found to give only two lines. The position of one of these lines depends on the ethanoic acid concentration, whereas the other one does not. Explain how you would expect the position of the concentration-dependent line to change over the range of ethanoic acid concentrations from $$0$$-$$100\%$$.

Exercise 9-28 The proton nmr spectrum of a compound of formula $$\ce{C_6H_{12}O_2}$$, is shown in Figure 9-31. The signals are shown relative to TMS as the standard, and the stepped line is the integral of the area under the peaks from left to right. The infrared spectrum of the same compound shows a broad band at $$3300 \: \text{cm}^{-1}$$ and a strong band at $$1700 \: \text{cm}^{-1}$$. Deduce the structure of the compound and name it by the IUPAC system.

Figure 9-31: Proton nmr spectrum of a compound, $$\ce{C_6H_{12}O_2}$$, at $$60 \: \text{MHz}$$ relative to TMS at $$0.00 \: \text{ppm}$$. The stepped line is the integral running from left to right. See Exercise 9-28.

Exercise 9-29 Sketch the proton chemical shifts in $$\text{ppm}$$ and $$\text{Hz}$$ as well as the integral you would expect for each of the following substances at $$60 \: \text{MHz}$$. (The spin-spin splitting of the resonance lines evident in Figures 9-23 and 9-27, but not seen in Figure 9-31, can be safely neglected with all of the compounds listed.)

a. $$\ce{(CH_3)_3CCH_2OCH_3}$$
b. $$\ce{CH_2COC(CH_3)_3}$$
c. $$\ce{HCOC(CH_3)_2CHO}$$
d.
e. $$\ce{(CH_3)_2C=CCl_2}$$
f. $$\ce{(CH_3)_3COC \equiv CH}$$
g. $$\ce{(CH_2Cl)_3CCO_2H}$$
h.* cis-1-methyl-4-tert-butyl-1,2,2,3,3,4,5,5,6,6-decachlorocyclohexane

Exercise 9-30 Write structures for compounds with the following descriptions (There may be more than one correct answer, but only one answer is required.)

a. $$\ce{C_2H_6O}$$ with one proton nmr shift
b. $$\ce{C_6H_{12}}$$ with one proton nmr shift
c. $$\ce{C_5H_{12}}$$ with one proton nmr shift
d. $$\ce{C_4H_8O}$$ with two different proton nmr shifts
e. $$\ce{C_4H_8O_2}$$ with three different proton nmr shifts
f. $$\ce{C_4Cl_8}$$ with two different $$\ce{^{13}C}$$ nmr shifts

Exercise 9-31 Sketch the proton nmr spectrum and integral expected at $$60 \: \text{MHz}$$, with TMS as standard, for the following substances. Show the line positions in $$\ce{Hz}$$; neglect spin-spin couplings smaller than $$1$$ to $$2 \: \text{Hz}$$ and all second-order effects. Remember that chlorine, bromine, and iodine (but not fluorine) act as nonmagnetic nuclei.

a. $$\ce{CH_3Cl}$$
b. $$\ce{CH_3CH_2Cl}$$
c. $$\ce{(CH_3)_2CHCl}$$
d. $$\ce{CH_3CCl_2CH_2Cl}$$
e. $$\ce{(CH_3)_3CCl}$$
f. $$\ce{CHCl_2CHBr_2}$$
g. $$\ce{CH_3CHClCOCH_3}$$
h. $$\ce{CH_3CH_2CO_2CH_2CH_3}$$
i. $$\ce{ClCH_2CH_2CH_2I}$$
j. $$\ce{(ClCH_2)_3CH}$$

Exercise 9-32* The proton-proton coupling in 1,1,2,2-tetrachloroethane cannot be observed directly because the chemical shift is zero. However, measurements of the splittings in $$\ce{^{13}CCl_2H-^{12}CCl_2H}$$ show that the proton-proton coupling in $$\ce{CHCl_2CHCl_2}$$ is $$3.1 \: \text{Hz}$$. Explain how you can use this information to deduce the favored conformation of $$\ce{CHCl_2CHCl_2}$$. Draw a sawhorse representation of the preferred conformation.

Exercise 9-33 The proton-proton coupling in meso-2,3-dibromobutanedioic acid (determined by the same procedure as for 1,1,2,2-tetrachloroethane, see Exercise 9-32) is $$11.9 \: \text{Hz}$$. Write a sawhorse structure for the preferred conformation of this molecule.

Exercise 9-34*

a. Show how the assignment of $$J_{AB} = J_{BC} = 2 J_{AC}$$ leads to the prediction of four equally spaced and equally intense lines for the methyl resonance of 2-phenylpropene.

b. What would the splittings of the alkenic and methyl protons look like for trans-1-phenylpropene if $$J_{AB} = 16 \: \text{Hz}$$, $$J_{AC} = 4 \: \text{Hz}$$, and $$J_{BC} = 0 \: \text{Hz}$$?

Exercise 9-35 Interpret fully each of the proton nmr spectra shown in Figure 9-40 in terms of the given structures. For spin-spin splittings, explain how the patterns arise and predict the intensities expected from simple theory.

Figure 9-40: Proton nmr spectra at $$60 \: \text{MHz}$$ relative to TMS $$= 0.00 \: \text{ppm}$$. See Exercise 9-35.

Exercise 9-36 Figure 9-41 shows proton nmr spectra and integrals at $$60 \: \text{MHz}$$ for three simple organic compounds. Write a structure for each substance that is in accord with both its molecular formula and nmr spectrum. Explain how you assign each of the lines in the nmr spectrum.

Figure 9-41: Proton nmr spectra and integrals for some simple organic compounds at $$60 \: \text{MHz}$$ relative to TMS, $$0.00 \: \text{ppm}$$. See Exercise 9-36.

Exercise 9-37 Figure 9-42 shows the proton nmr spectrum of a compound, $$\ce{C_5H_8O_2}$$. Which of the following structures fits the spectrum best? Explain. Remember that the protons of

are expected to be nonequivalent; that is, they have different chemical shifts if $$\ce{R}$$ and $$\ce{R'}$$ are different groups.

Figure 9-42: Proton spectrum of a compound, $$\ce{C_5H_8O_2}$$, at $$60 \: \text{MHz}$$ relative to TMS as standard. See Exercise 9-37.

Exercise 9-38 Suppose that you had six unlabeled bottles containing caffeine, hexachlorophene, phenacetin, DDT, 1,3-dimethyluracil, and 1-phenylethanamine. The nmr spectrum of each of these compounds is shown in Figure 9-43. Match the lettered spectra with the appropriate individual structures so the bottles can be labeled properly. Give your reasoning.

Figure 9-43: Proton nmr spectra of compounds at $$60 \: \text{MHz}$$. See Exercise 9-38.

Exercise 9-39 Show how one can use the asymmetry of the line intensities of the $$60$$-$$\text{MHz}$$ proton spectrum in Figure 9-45 to show which groups of lines are interconnected by spin-spin coupling. Write structural formulas for the compounds involved that fit the observed splitting patterns and chemical shifts.

Exercise 9-40 Explain why it is correct to characterize $$16$$ and $$17$$ as diastereomers and not enantiomers.

Exercise 9-41* When one takes the proton nmr spectrum of ordinary trichloromethane (chloroform, $$\ce{CHCl_3}$$) under high gain, the spectrum shown in Figure 9-49 is obtained. The weak outside peaks are separated by $$210 \: \text{Hz}$$ and together have an integrated intensity of slightly over $$1\%$$ of the main peak. Explain how these weak proton signals arise.

Figure 9-49: Proton nmr spectrum at $$60 \: \text{MHz}$$ of trichloromethane taken with high-detection sensitivity. See Exercise 9-41.

Exercise 9-42* With reference to the data summarized in Figure 9-47 and the discussion in Section 9-10L, sketch qualitatively the proton-decoupled $$\ce{^{13}C}$$ spectra you would expect for

a. $$\ce{(CH_3)_3CCH_2OH}$$
b. $$\ce{CCl_3CH_2OCOCH_3}$$

Exercise 9-43* Figure 9-50 shows the $$\ce{^1H}$$ and $$\ce{^{13}C}$$ nmr spectra of a compound $$\ce{C_6H_{10}O}$$. With the aid of these spectra, deduce the structure of $$\ce{C_6H_{10}O}$$. It will be seen that the $$\ce{^{13}C}$$ spectrum is quite simple, even though the proton spectrum is complex and difficult to interpret.

Figure 9-50: (a) Proton and (b) $$\ce{^{13}C}$$ spectra of a compound $$\ce{C_6H_{10}O}$$ taken at $$60 \: \text{MHz}$$ and $$15.1 \: \text{MHz}$$, respectively. Because of the special way the $$\ce{^{13}C}$$ spectrum was determined, the peak at $$209 \: \text{ppm}$$ is smaller than it should be. The intensity of this peak is, correctly, the same as the peak at $$25.5 \: \text{ppm}$$. See Exercise 9-43.

Exercise 9-44 Explain how a mass spectrometer, capable of distinguishing between ions with $$m/e$$ values differing by one part in 50,000, could be used to tell whether an ion of mass 29 is $$\ce{C_2H_5^+}$$ or $$\ce{CHO^+}$$.

Exercise 9-45

a. Calculate the relative intensities of the $$\left( \ce{M} + 1 \right)^+$$ and $$\left( \ce{M} + 2 \right)^+$$ ions for a molecule of elemental composition $$\ce{C_3H_7NO_2}$$.

b. The $$\ce{M}^+$$, $$\left( \ce{M} + 1 \right)^+$$, and $$\left( \ce{M} + 2 \right)^+$$ ion intensities were measured as 100, 8.84, and 0.54 respectively, and the molecular weight as 120. What is the molecular formula of the compound?

c. In our example of how natural $$\ce{^{13}C}$$ can be used to determine the number of carbon atoms in a compound with $$\ce{M}^+ = 86$$ and a $$\left( \ce{M} + 1 \right)^+/\ce{M}^+$$ ratio of 6.6/100, we neglected the possible contribution to the $$\left( \ce{M} + 1 \right)^+$$ peak of the hydrogen isotope of mass 2 (deuterium). The natural abundance of deuterium is $$0.015\%$$. For a compound of composition $$\ce{C_6H_{14}}$$, how much do you expect the deuterium to contribute to the intensity of the $$\left( \ce{M} + 1 \right)^+$$ peak relative to the $$\ce{M}^+$$ peak?

Exercise 9-46 Show how the molecular weights of 2-propanone, propanal, and 2-butanone can be estimated from the mass spectra in Figure 9-52. Suggest a possible origin for the strong peaks of mass 57 in the spectra of propanal and 2-butanone, which is essentially absent in 2-propanone, although 2-propanone (and 2-butanone) show strong peaks at mass 43.

Exercise 9-47 The mass spectrum of propylbenzene has a prominent peak at mass number 92. With (3,3,3-trideuteriopropyl)benzene, this peak shifts to 93. Write a likely mechanism for breakdown of propylbenzene to give a fragment of mass number 92.

Exercise 9-48 The mass spectra of alcohols usually show peaks of $$\left( \ce{M} - 18 \right)$$, which correspond to loss of water. What kind of mechanisms can explain the formation of $$\left( \ce{M} - 18 \right)$$ peaks, and no $$\left( \ce{M} - 19 \right)$$ peaks, from 1,1-dideuterioethanol and 1,1,1,3,3-pentadeuterio-2-butanol?

Exercise 9-49 Explain how the postulated rearrangement of the $$\ce{M}^+$$ ion of ethyl butanoate (Section 9-11) is supported by the fact that the 2,2-dideuterio compound gives a peak with $$m/e =$$ 90, the 3,3-dideuterio isomer gives a $$m/e$$ 88 peak, while the 4,4,4-trideuterio isomer gives a $$m/e$$ 89 peak.

Exercise 9-50 What is the likely structure for the major fragment ion with $$m/e =$$ 45 derived from methoxyethane (methyl ethyl ether) on electron impact?

Exercise 9-51 A certain halogen compound gave a mass spectrum with molecular ion peaks at $$m/e$$ 136 and 138 in about equal intensities. The nmr spectrum of this compound gave only a single resonance around $$1.2 \: \text{ppm}$$. What is the structure of the compound? Give your reasoning.

Exercise 9-52* The mass spectra of three compounds, A, B, and C, are given below in tabular form. Only the peaks of significant intensity are reported.

a. Compound A is $$\ce{CH_3CH_2CH_2COCH_3}$$. Show how this material can fragment to give the peaks marked with an asterisk and, where possible, how the isotope peaks help establish your assignments.

b. Determine the molecular weight and the molecular formula of Compounds B and C from the spectral data. Suggest a likely structure for each peak marked with an asterisk.

## Contributors

• John D. Robert and Marjorie C. Caserio (1977) Basic Principles of Organic Chemistry, second edition. W. A. Benjamin, Inc. , Menlo Park, CA. ISBN 0-8053-8329-8. This content is copyrighted under the following conditions, "You are granted permission for individual, educational, research and non-commercial reproduction, distribution, display and performance of this work in any format."