Solved: a. How could you use IR spectroscopy to determine whether the following reaction

Which of the following fragments produced in a mass spectrometer will be accelerated through the analyzer tube? CH3CH2 CH3CH2CH2 CH2CH CH2 + [CH3CH2CH3] + + CH2CH CH2

What distinguishes the mass spectrum of 2,2-dimethylpropane from the mass spectra of pentane and isopentane?

What is the most likely m/z value for the base peak in the mass spectrum of 3-methylpentane?

Draw possible structures for an ester that has a molecular ion with an m/z value of 74.

Determine the molecular formula for each of the following: a. a compound that contains only C and H and has a molecular ion with an m/z value of 72 b. a compound that contains C, H, and one O and has a molecular ion with an m/z value of 100 c. a compound that contains C, H, and two Os and has a molecular ion with an m/z value of 102 d. an amide that has a molecular ion with an m/z value of 115

a. Suggest possible molecular formulas for a compound that has a molecular ion with an m/z value of 86. b. Can one of the possible molecular formulas contain a nitrogen atom?

If a compound has a molecular ion with an odd-numbered mass, then the compound contains an odd number of nitrogen atoms. This is known as the nitrogen rule. a. Calculate the m/z value for the molecular ion of each of the following compounds: 1. NH2 2. H2N NH2 b. Explain why the nitrogen rule holds. c. State the rule in terms of a molecular ion with an even-numbered mass.

Identify the hydrocarbon that has a molecular ion with an m/z value of 128, a base peak with an m/z value of 43, and significant peaks with m/z values of 57, 71, and 85.

Predict the relative intensities of the molecular ion peak, the M+2 peak, and the M+4 peak for a compound that contains two bromine atoms.

Which molecular formula has an exact molecular mass of 86.1096 amu: C6H14, C4H10N2, or C4H6O2?

a. Can a low-resolution mass spectrometer distinguish between C2H5 + and CHO+ ? b. Can a high-resolution mass spectrometer distinguish between them?

Sketch the mass spectrum expected for 1-chloropropane.

The mass spectra of 1-methoxybutane, 2-methoxybutane, and 2-methoxy-2-methylpropane are shown below. Match each compound with its spectrum.

Primary alcohols have a strong peak at m/z = 31. a. What fragment is responsible for this peak? b. Draw the mechanism for its formation.

Identify the ketones responsible for the mass spectra below.

Draw the mechanism for formation of the fragments that would allow these ketones to be distinguished by their mass spectra.

Using curved arrows, show the principal fragments you would expect to see in the mass spectrum of each of the following compounds:

The reaction of (Z)-2-pentene with water and a trace of H2SO4 forms two products. Identify the products from their mass spectra.

a. Which is higher in energy: electromagnetic radiation with wavenumber 100 cm1 or with wavenumber 2000 cm1? b. Which is higher in energy: electromagnetic radiation with wavelength 950 nm or with wavelength 850 nm?

One of the following depicts the waves associated with infrared radiation, and one depicts the waves associated with visible light. Which is which?

a. Which occurs at a larger wavenumber: 1. a CC stretch or a CC stretch? 3. a CN stretch or a CN stretch? 2. a CH stretch or a CH bend? 4. a CO stretch or a CO stretch?"b. Assuming that the force constants are the same, which occurs at a larger wavenumber: 1. a CO stretch or a CCl stretch? 2. a CO stretch or a CC stretch?"

Which occurs at a larger wavenumber: a. the CO stretch of phenol or the CO stretch of cyclohexanol? b. the CO stretch of a ketone or the CO stretch of an amide? c. the CN stretch of cyclohexylamine or the CN stretch of aniline?

Which shows an absorption band at a larger wavenumber: a carbonyl group bonded to an sp3 carbon or a carbonyl group bonded to an sp2 carbon of an alkene?

Why is the CO absorption band of 1-hexanol at a smaller wavenumber (1060 cm-1) than the CO absorption band of pentanoic acid (1220 cm-1)?

Rank the following compounds from highest wavenumber to lowest wavenumber for their CO absorption bands:

Which shows an OH stretch at a larger wavenumber: ethanol dissolved in carbon disulfide or an undiluted sample of ethanol?

How do you know that the absorption band at ~1100 cm-1 in Figure 13.23 is due to a CO bond and not to a CN bond?

a. An oxygen-containing compound shows an absorption band at ~1700 cm-1 and no absorption bands at ~3300 cm-1, ~2700 cm-1, or ~1100 cm-1. What class of compound is it? b. A nitrogen-containing compound shows no absorption band at ~3400 cm-1 and no absorption bands between ~1700 cm-1 and ~1600 cm-1 or between 2260 cm-1 and 2220 cm-1. What class of compound is it?

How can IR spectroscopy be used to distinguish between the following compounds? a. a ketone and an aldehyde b. a cyclic ketone and an open-chain ketone c. benzene and cyclohexene d. cis-2-hexene and trans-2-hexene e. cyclohexene and cyclohexane f. a primary amine and a tertiary amine

For each of the following pairs of compounds, name one absorption band that can be used to distinguish between them.

Which of the following compounds has a vibration that is infrared inactive? 1-butyne, 2-butyne, H2, H2O, Cl2, and ethene

Identify the compound that gives the mass spectrum and infrared spectrum shown here.

A compound with molecular formula C4H6O gives the infrared spectrum shown here. Identify the compound.

A solution of a compound in ethanol shows an absorbance of 0.52 at 236 nm in a cell with a 1 cm light path. Its molar absorptivity in ethanol at that wavelength is 12,600 M-1 cm-1. What is the concentration of the compound?

4.0 * 10-5 M solution of a compound in hexane shows an absorbance of 0.40 at 252 nm in a cell with a 1 cm light path. What is the molar absorptivity of the compound in hexane at 252 nm?

Predict the lmax of the following compound: O

Rank each set of compounds in order of decreasing lmax:

a. At pH = 7, one of the ions shown here is purple and the other is blue. Which is which? (Hint: refer to the color spectrum in Figure 13.8 on page 584.) b. What would be the difference in the colors of the compounds at pH = 3?

Describe a way to determine the rate of the alcohol dehydrogenase catalyzed oxidation of ethanol by NAD+ .

pH values. Its conjugate base is the only species in the solution that absorbs UV light at the wavelength used. Estimate the pKa of the acid from the data obtained. pH 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 Absorbance 0 0 0.10 0.50 0.80 1.10 1.50 1.60 1.60 1.60

41. In the mass spectrum of the following compounds, which is the tallestthe peak at m/z = 57 or the peak at m/z = 71? a. 3-methylpentane b. 2-methylpentane

List three factors that influence the intensity of an IR absorption band.

Draw structures for a saturated hydrocarbon that has a molecular ion with an m/z value of 128.

Rank the following compounds in order of increasing lmax:

For each of the following pairs of compounds, identify one IR absorption band that could be used to distinguish between them:

a. How could you use IR spectroscopy to determine whether the following reaction had occurred? b. After purifying the product, how could you determine whether all the NH2NH2 had been removed?

Assuming that the force constant is approximately the same for CC, CN, and CO bonds, predict the relative positions of their stretching vibrations in an IR spectrum.

Norlutin and Enovid are ketones that suppress ovulation, so they have been used clinically as contraceptives. For which of these compounds would you expect the infrared carbonyl absorption (CO stretch) to be at a higher frequency? Explain.

In the following boxes, list the types of bonds and the approximate wavenumber at which each type of bond is expected to show an IR absorption:

A mass spectrum shows significant peaks at m>z = 87, 115, 140, and 143. Which of the following compounds is responsible for that mass spectrum?

How could IR spectroscopy distinguish between 1,5-hexadiene and 2,4-hexadiene?

A compound gives a mass spectrum with essentially only three peaks at m/z = 77 (40%), 112 (100%), and 114 (33%). Identify the compound.

What hydrocarbons that contain a six-membered ring will have a molecular ion peak at m/z = 112?

The IR spectrum of a compound with molecular formula C5H8O is shown below. Identify the compound.

Rank the following compounds from highest wavenumber to lowest wavenumber for their CO absorption band:

Rank the following compounds from highest wavenumber to lowest wavenumber for their CO absorption band:

What peaks in their mass spectra can be used to distinguish between the following compounds?

The mass spectrum for a compound with molecular weight of 102 is shown below. Its IR spectrum has a broad, strong absorption at 3600 cm1 and a medium absorption at 1360 cm1. a. Identify the compound. b. Show the mechanism for formation of the peak at m/z = 84.

Which one of the following five compounds produced the IR spectrum shown below?

The IR spectrum of compound A with a molecular formula of C5H12O is shown below. Compound A is oxidized to give compound B, a ketone with a molecular formula of C5H10O. When compound A is heated with H2SO4, compounds C and D are obtained. Considerably more D is obtained than C. Reaction of compound C with O3, followed by treatment with dimethyl sulfide, gives two products: formaldehyde and compound E, with a molecular formula of C4H8O. Reaction of compound D with O3, followed by treatment with dimethyl sulfide, gives two products: compound F, with a molecular formula of C3H6O, and compound G, with a molecular formula of C2H4O. What are the structures of compounds A through G?

Each of the IR spectra shown below is accompanied by a set of four compounds. In each case, indicate which of the four compounds is responsible for the spectrum. a. O CH3CH2CH2C CCH3 CH3CH2CH2CH2OH CH3CH2CH2CH2C CH CH3CH2CH2COH

Five compounds are shown for each of the IR spectra below. Indicate which of the five compounds is responsible for each spectrum.

A compound is known to be one of those shown here. What absorption bands in its IR spectrum allow you to identify the compound?

How can IR spectroscopy distinguish between 1-hexyne, 2-hexyne, and 3-hexyne?

Draw a structure for a carboxylic acid that has a molecular ion with an m/z value of 116.

A solution of ethanol has been contaminated with benzenea technique employed to make ethanol unfit to drink. Benzene has a molar absorptivity of 230 M-1 cm-1 at 260 nm in ethanol, and ethanol shows no absorbance at 260 nm. How can the concentration of benzene in the solution be determined?

Give approximate wavenumbers for the major characteristic IR absorption bands that would be given by each of the following compounds:

Given that the force constants are similar for CH and CC bonds, explain why the stretching vibration of a CH bond occurs at a larger wavenumber.

Which one of the following five compounds produced the IR spectrum shown below?

Phenolphthalein is an acidbase indicator. In solutions of pH 6 8.5, it is colorless; in solutions of pH 7 8.5, it is deep red-purple. Account for the change in color.

Each of the IR spectra shown below is the spectrum of one of the following compounds. Identify the compound that produced each spectrum.

How can you use UV spectroscopy to distinguish between the compounds in each of the following pairs?

Calculate the approximate wavenumber at which a CC stretch occurs, given that the force constant for the CC bond is 1 * 106 g s-2.

The IR and mass spectra for three different compounds are shown below. Identify each compound.