Structure Determination: Mass Spectroscopy and Infrared Spectroscopy

One consequence of the base-catalyzed isomerization of unsaturated ketones described in Problem 22-55 is that 2-substituted 2-cyclopentenones can be interconverted with 5-substituted 2-cyclopentenones. Propose a mechanism for this isomerization.

The following two hydrocarbons have been isolated from various plants in the sunflower family. Name them according to IUPAC rules. 

What amino acid sequence is coded for by the following mRNA base sequence?

$\left(5^{\text{'}}\right)\mathbf{\text{CUA-GAC-CGU-UCC-AAG-UGA}}\left(3^{\text{'}}\right)$

Predict the products of the following reactions:

Draw the products you would expect from conrotatory and disrotatory cyclizations of (2Z,4Z,6Z)-2,4,6-octatriene. Which of the two paths would you expect the thermal reaction to follow?

Would you expect the following reaction to proceed in a conrotatory or
 disrotatory manner? Show the stereochemistry of the cyclobutene product, and explain your answer.

The Favorskii reaction involves the treatment of an -bromo ketone with a base to yield a ring-contracted product. For example, the reaction of 2-bromocyclohexanone with aqueous NaOH yields cyclopentanecarboxylic acid. Propose a mechanism.

Give IUPAC names for the following compounds

Predict the product(s) and provide the mechanism for each reaction below. What does each mechanism have in common?

Draw structures corresponding to the following IUPAC names:

a)cis-1,2-Cyclohexanedicarboxylic acid

b) Hepatanedioic acid

c) 2-Hexen-4-ynoic acid

d) 4-Ethyl-2-propyloctanoic acid

e) 3-chlorophthalic acid

f) Triphenylacetic acid

g) 2-Cyclobutenecarbonitrile

h) m-Benzoylbenzonitrile

Predict the products from reaction of 5-decyne with the following

reagents:

(a) ${\mathbf{H}}_{\mathbf{2}}$, Lindlar catalyst

(b) Li in ${\mathbf{NH}}_{\mathbf{3}}$ 

(c) 1 equiv ${\mathbf{Br}}_{\mathbf{2}}$

d) ${\mathbf{BH}}_{\mathbf{3}}$ in THF, then ${\mathbf{H}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{2}}$,$\mathbf{OH}$

(e) ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$, ${\mathbf{H}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$, ${\mathbf{HgSO}}_{\mathbf{4}}$

(f) Excess ${\mathbf{\text{H}}}_{\mathbf{2}}$, Pd/C catalyst

Draw and name the following

a) The eight carboxylic acids with the formula ${\mathit{C}}_{\mathbf{6}}{\mathit{H}}_{\mathbf{12}}{\mathit{O}}_{\mathbf{2}}$ 

b) Three nitriles with the formula  ${\mathit{C}}_{\mathbf{5}}{\mathit{H}}_{\mathbf{7}}\mathit{N}$

Predict the products from reaction of 2-hexyne with the following

reagents:

1. 2 equiv ${\mathbf{Br}}_{\mathbf{2}}$ 
2. 1 equiv HBr
3. Excess HBr
4. Li in  ${\mathbf{NH}}_{\mathbf{3}}$
5.  ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$, ${\mathbf{H}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$, ${\mathbf{HgSO}}_{\mathbf{4}}$ 

Amino acids can be prepared by reaction of alkyl halides with diethyl acetamidomalonate, followed by heating the initial alkylation product with aqueous HCl. Show how you would prepare alanine, ${\mathbf{CH}}_{\mathbf{3}}\mathbf{CH}\mathbf{\left(}{\mathbf{NH}}_{\mathbf{2}}\mathbf{\right)}{\mathbf{CO}}_{\mathbf{2}}\mathbf{H}$, one of the twenty amino acids found in proteins, and propose a mechanism for acid-catalyzed conversion of the initial alkylation product to the amino acid.

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

Predict the product(s) and provide the mechanism for each reaction below. What does each mechanism have in common?

     b. 

       c. 

     d. 

Identify all the acidic hydrogens ($\mathit{p}{\mathit{K}}_{\mathbf{a}}\mathbf{<}\mathbf{25}$) in the following molecules:

Base treatment of the following α,β-unsaturated carbonyl compound yields an anion by removal of H⁺ from the $\mathit{\gamma }$ carbon. Why are hydrogens on the $\mathit{\gamma }$  carbon atom acidic?

Treatment of 1-phenyl-2-propenone with a strong base such as LDA does not yield an anion, even though it contains a hydrogen on the carbon atom next to the carbonyl group. Explain.

Although the Diels–Alder reaction generally occurs between an electron rich diene and an electron-deficient dienophile, it is also possible to

have inverse-demand Diels–Alder reactions between suitable electrondeficient

conjugated double bonds and electron-rich alkenes. These reactions are particularly useful because they allow for the incorporation of heteroatoms into the new six-membered ring. Predict the products of each inverse-demand Diels–Alder reaction below. Be sure your products reflect the correct stereochemistry. If more than one region isomer is possible, draw both.

(a)

(b)

(c)

Assign Cahn–Ingold–Prelog rankings to the following sets of substituents

a.$\mathbf{-}\mathit{C}\mathit{H}\mathbf{=}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathbf{,}\mathbf{-}\mathit{C}\mathit{H}{\mathbf{\left(}\mathbf{C}{\mathbf{H}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{2}}\mathbf{,}\mathbf{-}\mathit{C}{\mathbf{\left(}\mathbf{C}{\mathbf{H}}_{\mathbf{3}}\mathbf{\right)}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{C}{\mathit{H}}_{\mathbf{3}}$

b.$\mathbf{-}\mathit{C}{\mathit{O}}_{\mathbf{2}}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}\mathit{O}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{O}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{C}{\mathit{H}}_{\mathbf{3}}$

c.$\mathbf{-}\mathit{C}{\mathit{O}}_{\mathbf{2}}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}\mathit{O}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{O}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{C}{\mathit{H}}_{\mathbf{3}}$

d.$\mathbf{-}\mathit{C}{\mathit{O}}_{\mathbf{2}}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}\mathit{O}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{O}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{C}{\mathit{H}}_{\mathbf{3}}$,$\mathbf{-}\mathit{C}{\mathit{O}}_{\mathbf{2}}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}\mathit{O}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{O}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{,}\mathbf{-}\mathit{C}{\mathit{H}}_{\mathbf{2}}\mathit{C}{\mathit{H}}_{\mathbf{3}}$

Rank the double bonds below in terms of increasing stability:

Aprobarbital, a barbiturate once used in treating insomnia, is synthesized in three steps from diethyl malonate. Show how you would synthesize the necessary dialkylated intermediate, and then propose a mechanism for the reaction of this intermediate with urea to give aprobarbital.

Draw the structure of an alkene that yields only acetone, ${\left(C{H}_3\right)}_{\mathbf{2}}\mathbf{C}\mathbf{=}\mathbf{O}$, on ozonolysis followed by treatment with Zn. 

Which of the following bases could be used to deprotonate 1-butyne?

(a) KOH

Predict the products of the reaction of (1) phenylacetaldehyde and (2) acetophenone with the following reagents:

1. ${\mathbf{NaBH}}_{\mathbf{4}}$, then  ${\mathbf{H}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}$
2.   Dess-Martin reagent
3. ${\mathbf{NH}}_{\mathbf{2}}\mathbf{OH}$, HCl catalyst
4. ${\mathbf{CH}}_{\mathbf{3}}\mathbf{MgBr}$, then ${\mathbf{H}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}$
5. $\mathbf{2}{\mathbf{CH}}_{\mathbf{3}}\mathbf{OH}$, HCl catalyst
6. ${\mathbf{H}}_{\mathbf{2}}{\mathbf{NNH}}_{\mathbf{2}}$, KOH
7. ${\left({\mathbf{C}}_{\mathbf{6}}{\mathbf{H}}_{\mathbf{5}}\right)}_{\mathbf{3}}\mathbf{P}\mathbf{=}{\mathbf{CH}}_{\mathbf{2}}$
   
8.  HCN, KCN

Show how you might use a Wittig reaction to prepare the following alkenes. Identify the alkyl halide and the carbonyl components.

a. 

b. 

Phenol,${\mathbf{C}}_{\mathbf{6}}{\mathbf{H}}_{\mathbf{5}}\mathbf{OH}$, is a stronger acid than methanol, ${\mathbf{CH}}_3\mathbf{OH}$, even though both contain an OH bond. Draw the structures of the anions resulting from loss of ${\mathbf{H}}^{\mathbf{+}}$ from phenol and methanol, and use resonance structures to explain the difference in acidity.

How would you prepare the following substances from 2-cyclohexenone? More than one step may be needed.

a. 

b. 

c. 

d.  

Question: 21-62 What is the structure of the polymer produced by treatment of $\mathbf{\beta }\mathbf{-}\mathbf{propiolactone}$ with a small amount of hydroxide ion?

How would you synthesize the following substances from benzaldehyde and any other reagents needed?

a. 

b. 

c. 

Question: 21-64 How would you distinguish spectroscopically between the following isomer pairs? Tell what differences you would expect to see.
 (a) N-Methylpropanamide and N,N-dimethylacetamide
 (b) 5-Hydroxypentanenitrile and cyclobutanecarboxamide
 (c) 4-Chlorobutanoic acid and 3-methoxypropanoyl chloride
(d) Ethyl propanoate and propyl acetate

Question: 21-65 Propose a structure for a compound, ${\mathbf{C}}_{\mathbf{4}\mathbf{ }}{\mathbf{H}}_{\mathbf{7}\mathbf{ }}{\mathbf{ClO}}_{\mathbf{2}}$ , that has the following

IR and ¹H NMR  spectra:

Question: 21-66 Assign structures to compounds with the following ¹H N MR  spectra:

$$\begin{gathered} \left(a\right){\mathbf{C}}_{\mathbf{4}}\mathbf{ }{\mathbf{H}}_{\mathbf{7}}\mathbf{ }\mathbf{ClO} \\ \mathbf{IR}\mathbf{ }\mathbf{:}\mathbf{1810}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}} \end{gathered}$$

$$\begin{gathered} \left(b\right){\mathbf{C}}_{\mathbf{6}\mathbf{ }}{\mathbf{H}}_{\mathbf{7}}\mathbf{ }{\mathbf{NO}}_{\mathbf{2}} \\ \mathbf{IR}\mathbf{:}\mathbf{2250}\mathbf{,}\mathbf{1735}\mathbf{ }{\mathbf{cm}}^{\mathbf{-}\mathbf{1}} \end{gathered}$$

1. Question: 21-67 The following reactivity order has been found for the basic hydrolysis of p-substituted methyl benzoates: $\mathit{Y}\mathbf{=}\mathit{N}{\mathit{O}}_{\mathbf{2}}\mathbf{>}\mathit{B}\mathit{r}\mathbf{>}\mathit{H}\mathbf{>}\mathit{C}{\mathit{H}}_{\mathbf{3}}\mathbf{>}\mathit{O}\mathit{C}{\mathit{H}}_{\mathbf{3}}$
2. How can you explain this reactivity order? Where would you expect $\mathit{Y}\mathbf{=}\mathit{C}\mathbf{=}\mathit{N}\mathbf{,}\mathbf{ }\mathit{Y}\mathbf{=}\mathit{C}\mathit{H}\mathit{O}\mathbf{,}\mathbf{ }\mathit{a}\mathit{n}\mathit{d}\mathit{Y}\mathbf{=}\mathit{N}{\mathit{H}}_{\mathbf{2}}$ to be in the reactivity list?

The male sex hormone testosterone contains only C, H, and O and has a mass of 288.2089 amu, as determined by high-resolution mass spectrometry. What is the likely molecular formula of testosterone?

Two mass spectra are shown in Figure 12-8. One spectrum is that of 2-methyl-2-pentene; the other is of 2-hexene. Which is which? Explain.

a. 

b.

What are the masses of the charged fragments produced in the following cleavage pathways? 

(a)Alpha cleavage of 2-pentanone  $\left({\mathbf{CH}}_3{\mathbf{COCH}}_2{\mathbf{CH}}_2{\mathbf{CH}}_3\right)$ 

(b) Dehydration of cyclohexanol (hydroxy cyclohexane) 

(c) McLafferty rearrangement of 4-methyl-2-pentanone  $\left[{\mathbf{CH}}_3{\mathbf{COCH}}_2\mathbf{CH}{\left({\mathbf{CH}}_3\right)}_2\right]$ 

(d) Alpha cleavage of triethylamine   $\mathbf{\left[}{\mathbf{\left(}{\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{\right)}}_{\mathbf{3}}\mathbf{N}\mathbf{\right]}$

Question: It’s useful to develop a feeling for the amounts of energy that correspond to different parts of the electromagnetic spectrum. Calculate the energies in kJ/mol of each of the following kinds of radiation: 

• (a) A gamma ray with $\lambda =5.0\times {10}^{-11}m$
• (b) An X-ray with $\lambda =3.0\times {10}^{-9}m$ 
• (c) Ultraviolet light with $v=6.0\times {10}^{15}Hz$
• (d) The visible light with $v=7.0\times {10}^{14}Hz$ .
• (e) Infrared radiation with $\lambda =2.0\times {10}^{-6}m$
• (f) Microwave radiation with $v=1.0\times {10}^{11}Hz$ .

Which has higher energy, infrared radiation with $\mathit{\lambda }\mathbf{=}\mathbf{1}\mathbf{.}\mathbf{0}\mathbf{\times }{\mathbf{10}}^{\mathbf{-}\mathbf{6}}\mathit{m}$ or an X-ray with $\mathit{\lambda }\mathbf{=}\mathbf{3}\mathbf{.}\mathbf{0}\mathbf{\times }{\mathbf{10}}^{\mathbf{-}\mathbf{9}}\mathit{m}$? Radiation with $\mathit{\nu }\mathbf{=}\mathbf{4}\mathbf{.}\mathbf{0}\mathbf{\times }{\mathbf{10}}^{\mathbf{9}}\mathit{H}\mathit{z}$ or with $\mathit{\lambda }\mathbf{=}\mathbf{9}\mathbf{.}\mathbf{0}\mathbf{\times }{\mathbf{10}}^{\mathbf{-}\mathbf{6}}\mathit{m}$?

What functional groups might the following molecules contain?

(a) A compound with a strong absorption at 1710 cm^-1 

(b) A compound with a strong absorption at 1540 cm^-1    

(c) A compound with strong absorptions at 1720 cm^-1   and 2500 to 3100 cm^-1    

Question: What functional groups might the following molecules contain?

(a) A compound with a strong absorption at 1710 ${\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$

(b) A compound with a strong absorption at 1540 ${\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$

(c) A compound with strong absorptions at 1720 ${\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ and 2500 to 3100  ${\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$

How might you use IR spectroscopy to distinguish between the followingpairs of isomers?

(a) CH₃ CH₂ OH and CH₃ OCH₃

(b) Cyclohexane and 1 - hexene

(c) CH₃ CH₂ CO₂ H and HOCH₂ CH₂ CHO

Question: How might you use IR spectroscopy to distinguish between the following pairs of isomers?

$$\begin{gathered} \mathbf{a}\mathbf{)}\mathbf{ }{\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH}\mathbf{ }\mathbf{and}\mathbf{ }{\mathbf{CH}}_{\mathbf{3}}{\mathbf{OCH}}_{\mathbf{3}} \\ \mathbf{b}\mathbf{)}\mathbf{ }\mathbf{cyclohexane}\mathbf{ }\mathbf{and}\mathbf{ }\mathbf{1}\mathbf{-}\mathbf{hexene} \\ \mathbf{c}\mathbf{)}\mathbf{ }{\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CO}}_{\mathbf{2}}\mathbf{H}\mathbf{ }\mathbf{and}\mathbf{ }{\mathbf{HOCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{CHO} \end{gathered}$$

How might you use IR spectroscopy to distinguish between the following pairs of isomers?

(a) \({\rm{C}}{{\rm{H}}_3}{\rm{C}}{{\rm{H}}_2}{\rm{OH and C}}{{\rm{H}}_3}{\rm{OC}}{{\rm{H}}_3}{\rm{ }}\) 

(b) \({\rm{Cyclohexane and 1 - hexene}}\)

(c) \({\rm{C}}{{\rm{H}}_3}{\rm{C}}{{\rm{H}}_2}{\rm{C}}{{\rm{O}}_2}{\rm{H and HOC}}{{\rm{H}}_2}{\rm{C}}{{\rm{H}}_2}{\rm{CHO}}\)

What functional groups might the following molecules contain? (a) A compound with a strong absorption at 1710${\mathrm{cm}}^{-1}$ (b) A compound with a strong absorption at 1540 ${\mathrm{cm}}^{-1}$ (c) A compound with strong absorptions at 1720 ${\mathrm{cm}}^{-1}$and 2500 to 3100 ${\mathrm{cm}}^{-1}$

The IR spectrum of phenylacetylene is shown in Figure 12-28. What absorptionbands can you identify?

The IR spectrum of phenylacetylene is shown in Figure 12-28. What absorption bands can you identify?

Question: The IR spectrum of phenylacetylene is shown in Figure 12-28. What absorption bands can you identify? 

Where might the following compounds have IR absorptions?