There are five constitutional isomers with molecular

All of the following compounds absorb IR radiation in the range between 1600 and 1850 cm-1 . In each case, identify the specific bond(s) responsible for the absorption(s) and predict the approximate wavenumber of absorption for each of those bonds. O (a) O (b) O O (c) O O (d) (e)

Rank each of the bonds identified in order of increasing wavenumber. O H O N H OH H R C N

Identify the signals you would expect in the diagnostic region of the IR spectrum for each of the following compounds: N O (a) O (b) O H (c) OH O (d)

Identify how IR spectroscopy might be used to monitor the progress of each of the following reactions: (a) H2 Pt OH O (b) [O] O O O MCPBA (c) O H H O (d) 1) O3 2) DMS + Br (e) t-BuOK

Identify the characteristic signals that you would expect in the diagnostic region of an IR spectrum of each of the following compounds: O (a) O (b) O (c) OH (d) OH O (e) OH O (f)

dentify the molecular formula for each of the following compounds and then predict the mass of the expected molecular ion in the mass spectrum of each compound: (a) OH (b) O (c) O (d) (e) N

Propose a molecular formula for a compound that has one degree of unsaturation and a mass spectrum that displays a molecular ion signal at m/z = 86.

The mass spectrum of an unknown hydrocarbon exhibits an (M+1)+ peak that is 10% as tall as the molecular ion peak. Identify the number of carbon atoms in the unknown compound.

Match each compound with the appropriate spectrum. Cl NH2 OH Br (a) m/z 10 20 30 40 50 60 70 80 90 Relative Intensity 0 20 40 60 80 100 (b) m/z 10 20 4030 1101009080706050 Relative Intensity 0 20 40 60 80 100 (c) m/z 10 20 30 40 50 60 70 80 90 Relative Intensity 0 20 40 60 80 100 (d) m/z 25 50 75 100 125 150 175 Relative Intensity 0 20 40 60 80 100

The sex attractant of the codling moth gives an IR spectrum with a broad signal between 3200 and 3600 cm-1 and two signals between 1600 and 1700 cm-1 . In the mass spectrum of this compound, the molecular ion peak appears at m/z = 196, and the relative abundances of the molecular ion and the (M+1)+ peak are 27.2% and 3.9%, respectively. (a) What functional groups are present in this compound? (b) How many carbon atoms are present in the compound? (c) Based on the information given, propose a molecular formula for the compound.

Compare the structures of cyclohexane and 2-methyl-2- pentene. (a) What is the molecular formula of each compound? (b) What is the HDI of each compound? (c) Can high-resolution mass spectrometry be used to distinguish between these compounds? Explain. (d) How would you differentiate between these two compounds using IR spectroscopy?

The mass spectrum of 1-ethyl-1-methylcyclohexane shows many fragments, with two in very large abundance. One appears at m/z = 111 and the other appears at m/z = 97. Identify the structure of each of these fragments.

The mass spectrum of 2-bromopentane shows many fragments. (a) One fragment appears at M79. Would you expect a signal at M77 that is equal in height to the M79 peak? Explain. (b) A fragment appears at M15. Would you expect a signal at M13 that is equal in height to the M15 peak? Explain. (c) One fragment appears at M29. Would you expect a signal at M27 that is equal in height to the M29 peak? Explain.

When treated with a strong base, 2-bromo-2,3-dimethylbutane will undergo an elimination reaction to produce two products. The choice of base (ethoxide vs. tert-butoxide) will determine which of the two products predominates. Draw both products and determine how you could distinguish between them using IR spectroscopy.

Propose a molecular formula that fits the following data: (a) A hydrocarbon (CxHy) with a molecular ion peak at m/z = 66 (b) A compound that absorbs IR radiation at 1720 cm-1 and exhibits a molecular ion peak at m/z = 70

The following is a mass spectrum of octane. (a) Which peak represents the molecular ion? (b) Which peak is the base peak? (c) Draw the structure of the fragment that produces the base peak. m/z 10 20 4030 1101009080706050 Relative Intensity 0 20 40 60 80 100

Calculate the HDI for each molecular formula. (a) C4H6 (b) C5H8 (c) C40H78 (d) C72H74 (e) C6H6O2 (f) C7H9NO2 (g) C8H10N2O (h) C5H7Cl3 ( i ) C6H5Br (j) C6H12O6

Propose two possible structures for a compound with molecular formula C5H8 that produces an IR signal at 3300 cm-1 .

Limonene is a hydrocarbon found in the peels of lemons and contributes significantly to the smell of lemons. Limonene has a molecular ion peak at m/z = 136 in its mass spectrum, and it has two double bonds and one ring in its structure. What is the molecular formula of limonene?

Explain how you would use IR spectroscopy to distinguish between 1-bromo-3-methyl-2-butene and 2-bromo-3-methyl-2-butene.

A dilute solution of 1,3-pentanediol does not produce the characteristic IR signal for a dilute alcohol. Rather, it produces a signal that is characteristic of a concentrated alcohol. Explain.

The following are IR and mass spectra of an unknown compound. Propose at least two possible structures for the unknown compound. Wavenumber (cm1) 4000 3500 3000 2500 2000 1500 1000 500 % Transmittance 0 20 40 60 80 100 m/z 10 20 30 40 50 60 70 80 90 100 Relative Intensity 0 20 40 60 80 100

The following are IR and mass spectra of an unknown compound. Propose at least two possible structures for the unknown compound. Wavenumber (cm1) 4000 3500 3000 2500 2000 1500 1000 500 % Transmittance 0 20 40 60 80 100 m/z 10 20 30 40 50 60 70 80 Relative Intensity 0 20 40 60 80 100

Consider the following sequence of reactions: E D C F TsCl py B G A Cl 1) MeMgBr 2) H2O 1) BH3 THF 2) H2O2, NaOH NaOEt MCPBA t-BuOK 1) NaH 2) MeI (a) Explain how you could use IR spectroscopy to differentiate between compounds F and G. (b) Explain how you could use IR spectroscopy to differentiate between compounds D and E. (c) If you wanted to distinguish between compounds B and F, would it be more suitable to use IR spectroscopy or mass spectrometry? Explain. (d) Would mass spectrometry be helpful for distinguishing between compounds A and D? Explain.

There are five constitutional isomers with molecular formula C4H8. One of the isomers exhibits a particularly strong signal at M15 in its mass spectrum. Identify this isomer and explain why the signal at M15 is so strong.

There are four isomers with molecular formula C4H9Cl. Only one of these isomers (compound A) has a chirality center. When compound A is treated with sodium ethoxide, three products are formed: compounds B, C, and D. Compounds B and C are diastereomers, with compound B being the less stable diastereomer. Do you expect compound D to exhibit a signal at approximately 1650 cm-1 in its IR spectrum? Explain.

Chloramphenicol is an antibiotic agent isolated from the Streptomyces venezuelae bacterium. Predict the expected isotope pattern in the mass spectrum of this compound (the relative heights of the molecular ion peak and surrounding peaks). Chloramphenicol O2N OH N H O OH Cl C

Ephedrine is a bronchodilator and decongestant obtained from the Chinese plant Ephedra sinica. A concentrated solution of ephedrine gives an IR spectrum with a broad signal between 3200 and 3600 cm-1 . An IR spectrum of a dilute solution of ephedrine is very similar to the IR spectrum of the concentrated solution. That is, the broad signal between 3200 and 3600 cm-1 is not transformed into a narrow signal, as we might expect for a compound containing an OH group. Explain. OH N H Ephedrine

Predict the expected isotope pattern in the mass spectrum of a compound with molecular formula C90H180Br2.

Esters contain two C!O bonds and therefore will produce two separate stretching signals in the fingerprint region of an IR spectrum. One of these signals typically appears at approximately 1000 cm-1 , while the other appears at approximately 1300 cm-1 . Predict which of the two C!O bonds produces the higher energy signal. Using principles that we learned in this chapter (factors that affect the wavenumber of absorption), offer two separate explanations for your choice.

Treating 1,2-cyclohexanediol with concentrated sulfuric acid yields a product with molecular formula C6H10O. An IR spectrum of the product exhibits a strong signal at 1720 cm-1 . Identify the structure of the product and show a mechanism for its formation.

Draw the expected isotope pattern that would be observed in the mass spectrum of CH2BrCl. In other words, predict the relative heights of the peaks at M, M+2, and M+4.

The following is the proposed structure of a blue fabric dye, based on high-resolution mass spectrometry data (Anal. Chem. 2013, 85, 831836). The reported method employed a pulsed laser to desorb dye molecules directly from a sample of dyed fabric. These molecules then entered a high- resolution mass spectrometer in negative ion mode (where anions are detected instead of cations). The resulting spectrum included the following peaks and relative intensities: m/z = 423.0647 (100%), 424.0681 (22.5%), and 425.0605 (4.21%). O O H2N HN S O O O O @ (a) Explain the origins and relative abundance of each of these peaks. Note that the two most abundant isotopes of sulfur are 32S (31.9721 amu, 95.02%) and 34S (33.9679 amu, 4.21%). (b) The mass spectrum also includes a signal at m/z = 425.0715. Explain the origin of this signal.

The base peak of a low-resolution spectrum of cyclohexanone is at m/z = 55. A high-resolution spectrum reveals that this peak actually consists of two peaks at 55.0183 and 55.0546 with relative intensities of 86.7 and 13.3, respectively (Appl. Spectrosc. 1960, 14, 9597). For each of these two peaks, propose a formula for the ion responsible for the peak. O Cyclohexanone

Compound A exists in equilibrium with its tautomeric form, compound B. An IR spectrum of a mixture of A and B exhibits four signals in the region 1600-1850 cm-1 . These signals appear at 1620, 1660, 1720, and 1740 cm-1 (J. Am. Chem. Soc. 1952, 74, 40704073). O OH O A B C OEt O OEt O O OEt O EtO (a) Identify the source for each of these four signals and provide a justification for the location of the signal at 1660 cm-1 . (b) For most simple ketones, the concentration of the enol tautomer is almost negligible at equilibrium. However, in this case, the concentration of B is significant. Provide a justification for this observation. (c) The IR spectrum of compound C lacks a signal at 1720 cm-1 . Draw the tautomer of C and then determine which tautomeric form predominates at equilibrium. Explain your choice.

As part of a study on cyclopropane derivatives of fatty acids, the following amide was subjected to mass spectrometric analysis (J. Org. Chem. 1977, 42, 126129). The most abundant peak in the spectrum was found at m/z = 113. Suggest a reasonable structure and mechanism of formation for the ion consistent with the peak at m/z = 113. O N

Pinolenic acid (C17H29CO2H) is an unbranched carboxylic acid with three cis alkene groups. It is found in pine nuts and is sometimes used in weight loss regimens as a hunger suppressant. Not every mass spectrometry technique requires ionization through ejection of single electrons; some instruments rely instead on milder ionization methods such as protonation or deprotonation to form charged species. Mass spectra of pinolenic acid were collected in positive ion mode (using conditions facilitating protonation) and in negative ion mode (using conditions facilitating deprotonation). A small amount of ozone was present in both experiments. Significant peaks in positive ion mode included m/z = 279, 211, 171, and 117. In the absence of ozone, however, only the peak at 279 remains (Anal. Chem. 2011, 83, 47384744). (a) Draw the structure of pinolenic acid as well as the ionic structures consistent with each of the peaks listed. (b) Predict m/z values for four significant peaks in negative ion mode, specifying the ion responsible for each peak.

The following two isomers were each subjected to mass spectrometric analysis. Some of the significant peaks from each of the two spectra are presented below (J. Chem. Ed. 2008, 85, 832833). Match each isomer (A, B) to its corresponding mass spectrometry data (X, Y) and provide structural assignments for every peak. Sample X, m/z = 202, 200, 187, 185, 159, 157, 121 Sample Y, m/z = 202, 200, 171, 169, 121 Br OH Br OH A B

Myosmine can be isolated from tobacco, along with several other structurally similar compounds, including nicotine. The originally accepted structure for myosmine was disproven with IR spectroscopy (Anal. Chem. 1954, 26, 14281431): N N Originally accepted H structure of myosmine :DYHQXPEHU FP?? ???? ???? ???? ???? ???? ???? ???? ? 7UDQVPLWWDQFH (a) Explain why the IR spectrum is not consistent with the originally proposed structure. (b) The discord between the proposed structure and its IR spectrum was resolved by recognizing that myosmine exists primarily as a tautomer of the proposed structure. Draw this tautomer and explain why its structure is more consistent with the observed IR spectrum. (c) Identify a likely source for the fairly intense signal at 1621 cm-1 .

Compound 1 contains a tetrazole ring (a ring containing four nitrogen atoms), while its constitutional isomer, compound 2, exhibits an azido group (N3). Compounds 1 and 2 rapidly interconvert, and IR spectroscopy provides evidence that the equilibrium greatly favors the tetrazole in this case (J. Am. Chem. Soc. 1959, 81, 46714673). Specifically, the IR spectrum of compound 1 lacks a signal in the region 21202160 cm-1 . Explain why the absence of a signal in this region provides evidence that 1 is favored over 2. N N N N 1 2 N N N N @ !

The IR spectrum of a dilute solution of compound 1 (in CS2) exhibits a signal at 3617 cm-1 , while the IR spectrum of a dilute solution of compound 2 exhibits a signal at 3594 cm-1 (J. Am. Chem. Soc. 1957, 79, 243247). H H H CH3 H CH3 CH3 R HO Cl H H H H CH3 R Cl HO 1 2 (a) Explain why the latter signal appears at a lower wavenumber of absorption. (b) Identify the signal that you expect to be broader. Explain your choice.

Phospholipids are a class of compounds largely responsible for the bilayer structure of cell membranes of plants and animals (discussed in Chapter 26). The phospholipid shown below has two unbranched hydrocarbon chains, one of which contains an alkene group with a cis configuration. A mass spectrum of this phospholipid in negative ion mode (where anions are detected instead of cations) shows a peak for the molecular ion at m/z = 673. When ozone is present, a new peak appears at m/z = 563 (J. Am. Chem. Soc. 2006, 128, 5859). O O O O C17H33 C15H31 O P O O HO @ (a) Draw the full structure of the phospholipid (indicating the position of the alkene group) consistent with these data. (b) When methanol is used as a solvent in the experiment with ozone present, the appearance of the peak at m/z 563 is accompanied by a peak at m/z = 611. When the solvent is changed to ethanol, the peak at m/z = 563 remains, but the peak at m/z = 611 is shifted to 625. Propose an explanation consistent with these findings.