Structure Determination: Mass Spectroscopy and Infrared Spectroscopy

Question: Where might the following compounds have IR absorptions?

Where might the following compound have IR absorptions?

Where might the following compound have IR absorptions?

Question: Where might the following compound have IR absorptions?

Where might the following compounds have IR absorptions?

The amount of energy required to spin-flip a nucleus depends both on the strength of the external magnetic field and on the nucleus. At a field strength

of 4.7 T, rf energy of 200 MHz is required to bring a nucleus into resonance,

but energy of only 187 MHz will bring a nucleus into resonance. Calculate

the amount of energy required to spin-flip a nucleus. Is this amount greater

or less than that required to spin-flip a nucleus?

At what approximate positions might the following compounds show IR absorptions?

(d) 

Where might the following compound have IR absorptions?

Question: Propose structures for compounds that meet the following descriptions:

       (a) An optically active compound $C_5{H}_{10}O$ with an IR absorption at $1730c{m}^{-1}$ .

       (b)  A non-optically active compound $C_5{H}_{9}N$  with an IR absorption at $2215c{m}^{-1}$

Where might the following compound have IR absorptions?

Show the structures of the fragments you would expect in the mass spectra of the following molecules:

Question: Where might the following compound have IR absorptions?

Question: The infrared spectrum of the compound with the mass spectrum shown below has strong absorbances at 1584, 1478, and . Propose a

structure consistent with the data.

Question: Camphor, a saturated monoketone from the Asian camphor tree, is used among other things as a moth repellent and as a constituent of embalming

fluid. If camphor has M⁺=152.1201 by high-resolution mass spectrometry,

what is its molecular formula? How many rings does camphor

have?

Question: The nitrogen rule of mass spectrometry says that a compound containing an odd number of nitrogen’s has an odd-numbered molecular ion.

Conversely, a compound containing an even number of nitrogen’s has

an even-numbered M⁺peak. Explain.

Question: Halogenated compounds are particularly easy to identify by their mass

spectra because both chlorine and bromine occur naturally as mixtures

of two abundant isotopes. Recall that chlorine occurs as ³⁵Cl (75.8%)

and ³⁷C (24.2%); and bromine occurs as ⁷⁹Br (50.7%) and ⁸¹Br (49.3%).

At what masses do the molecular ions occur for the following formulas?

What are the relative percentages of each molecular ion?

(a) Bromomethane, CH₃Br

(b) 1-Chlorohexane, C₆H₁₃Cl

Question: By knowing the natural abundances of minor isotopes, it’s possible to

calculate the relative heights of and M +1 peaks. If ¹³C has a natural

abundance of 1.10%, what are the relative heights of the and

M +1 peaks in the mass spectrum of benzene, C₆H₆?

Show the structures of the fragments you would expect in the mass

spectra of the following molecules:

Question: Show the structures of the fragments you would expect in the mass spectra of the following molecules:

Propose structures for compounds that fit the following mass-spectraldata:

(a) A hydrocarbon with M⁺ = 132

(b) A hydrocarbon with M⁺ = 166

(c) A hydrocarbon with M⁺ =  84

Question: Propose structures for compounds that fit the following mass-spectral data:

(a) A hydrocarbon with ${\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{132}$ 

(b) A hydrocarbon with ${\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{166}$

(c) A hydrocarbon with  ${\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{84}$

Write molecular formulas for compounds that show the following molecularions in their high-resolution mass spectra, assuming that C, H, N,and O might be present. The exact atomic masses are: 1.00783(¹H), 12.00000(¹²C)  , 14.00307 (¹⁴N) , 15.99491(¹⁶O)  .

(a) M+ = 98.0844

(b) M⁺ = 123.0320

Question: Write molecular formulas for compounds that show the following molecular ions in their high-resolution mass spectra, assuming that C, H, N, and O might be present. The exact atomic masses are: 1.00783 $\left({}_{}{}^{1}H\right)$ , 12.00000 $\left({}_{}{}^{12}C\right)$, 14.00307 $\left({}_{}{}^{14}N\right)$ , 15.99491 $\left({}_{}{}^{16}O\right)$.

$$\begin{gathered} \mathbf{a}\mathbf{)}\mathbf{ }{\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{98}\mathbf{.}\mathbf{0844} \\ \mathbf{b}\mathbf{)}\mathbf{ }{\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{123}\mathbf{.}\mathbf{0320} \end{gathered}$$

Camphor, a saturated monoketone from the Asian camphor tree, is used among other things as a moth repellent and as a constituent of embalming fluid. If camphor has M⁺=152.1201 by high-resolution mass spectrometry, what is its molecular formula? How many rings does camphor have?

In light of the nitrogen rule mentioned in Problem 12-17, what is the molecular formula of pyridine, M⁺=79?

Nicotine is a diamino compound isolated from dried tobacco leaves. Nicotine has two rings and =162.1157 by high-resolution mass spectrometry. Give a molecular formula for nicotine, and calculate the number of double bonds.

The hormone cortisone contains C, H, and O, and shows a molecular ion at ${\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{360}\mathbf{.}\mathbf{1937}$by high-resolution mass spectrometry. What is the molecular formula of cortisone? (The degree of unsaturation for cortisone is 8.)

Question: 2-Methylpentane (C₆H₁₄)has the mass spectrum shown. Which peak

represents? Which is the base peak? Propose structures for fragment

ions of m/z =71, 57, 43, and 29. Why does the base peak have the mass it does?

Assume that you are in a laboratory carrying out the catalytic hydrogenation of cyclohexene to cyclohexane. How could you use a mass

spectrometer to determine when the reaction is finished?

What fragments might you expect in the mass spectra of the following compounds?

(b)

(c)

How might you use IR spectroscopy to distinguish among the three

isomers 1-butyne, 1, 3-butadiene, and 2-butyne?

Would you expect two enantiomers such as (R)-2-bromobutane and

(S)-2-bromobutane to have identical or different IR spectra? Explain.

Would you expect two diastereomers such as meso-2, 3dibromobutane

and (2R, 3R)-dibromobutane to have identical or different IR spectra? Explain.

Question: Propose structures for compounds that meet the following descriptions:

(a) ${\mathbf{C}}_{\mathbf{5}}{\mathbf{H}}_{\mathbf{8}}$with IR absorptions at 3300 and 2150$c{m}^{-1}$

(b) ${\mathbf{C}}_{\mathbf{4}}{\mathbf{H}}_{\mathbf{8}}\mathbf{O}$with a strong IR absorption at 3400 $c{m}^{-1}$

(c) ${\mathbf{C}}_{\mathbf{4}}{\mathbf{H}}_{\mathbf{8}}\mathbf{O}$with a strong IR absorption at 1715  $c{m}^{-1}$

(d) ${\mathbf{C}}_{\mathbf{8}}{\mathbf{H}}_{\mathbf{10}}$with IR absorptions at 1600 and 1500 $c{m}^{-1}$

Question: How could you use infrared spectroscopy to distinguish between the

following pairs of isomers?

(a) $\mathbf{HC}\equiv {\mathbf{CCH}}_{\mathbf{2}}{\mathbf{NH}}_{\mathbf{2}}{\mathbf{andCH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{C}\equiv \mathbf{N}$

(b) ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{COCH}}_{\mathbf{3}}{\mathbf{andCH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{CHO}$

Question: How could you use infrared spectroscopy to distinguish between the

following pairs of isomers?

(a) $\mathbf{HC}\equiv {\mathbf{CCH}}_{\mathbf{2}}{\mathbf{NH}}_{\mathbf{2}}{\mathbf{andCH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{C}\equiv \mathbf{N}$

(b) ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{COCH}}_{\mathbf{3}}{\mathbf{andCH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{CHO}$

Question: Two infrared spectra are shown. One is the spectrum of cyclohexane,

and the other is the spectrum of cyclohexene. Identify them, and

explain your answer.

(a) 

(b) 

Question: At what approximate positions might the following compounds show

IR absorptions?

(A)

(b)

(c)

(d)

(e)

Question: How would you use infrared spectroscopy to distinguish between the following pairs of constitutional isomers?

(a)

(b)

(c)

$$\begin{gathered} C{H}_3\equiv CC{H}_{3 } AND C{H}_{3}COC{H}_{2}C\equiv CH \\ C{H}_{3}COCH\equiv CHC{H}_3 AND C{H}_{3}COC{H}_{2}CH=C{H}_2 \\ C{H}_{3}C{H}_{2}CHO AND H_{2}C=CHOC{H}_3 \end{gathered}$$

Question: At what approximate positions might the following compounds show

IR absorptions?

(a) 

Question: At what approximate positions might the following compounds show

IR absorptions?

(b) 

Question: At what approximate positions might the following compounds show IR absorptions?

(f)

Question: At what approximate positions might the following compounds show IR absorptions?

(e)

Question: At what approximate positions might the following compounds show

IR absorptions?

(c)  

At what approximate positions might the following compounds show

IR absorptions?

Assume that you are carrying out the dehydration of 1-methyl cyclohexanol to yield 1-methyl cyclohexene. How could you use infrared spectroscopy to determine when the reaction is complete?

Assume that you are carrying out the base-induced dehydrobromination of 3-Bromo-3-methyl pentane (Section 11-7) to yield an alkene. How could you use IR spectroscopy to tell which of three possible elimination products is formed, if one includes E/Z isomers?

Which is stronger, the C=O bond in an ester () or the C=O bond in a saturated ketone ()? Explain

Carvone is an unsaturated ketone responsible for the odour of spearmint. If carvone has  in its mass spectrum and contains three double bonds and one ring, what is its molecular formula?

Carvone (Problem 12-39) has an intense infrared absorption at . What kind of ketone does carvone contain?