Structure Determination: Mass Spectroscopy and Infrared Spectroscopy

Predict the aldol reaction product of the following compounds:

Identify the functional groups in each of the following molecules:

Most stable organic species have tetravalent carbon atoms, but species with trivalent carbon atoms also exist. Carbocations are one such class of compounds. 

 (a) How many valence electrons does the positively charged carbon atom have?

 (b) What hybridization do you expect this carbon atom to have?

 (c) What geometry is the carbocation likely to have?

Propose structures for simple molecules that contain the following functional groups:

(a)Alcohol (b) Aromatic ring (c) Carboxylic acid (d) Amine (e) Both ketone and amine

(f) Two double bonds

Consider 2-methylbutane( isopentane) sighting along C-2, C-3 bond:

1. Draw a Newman Projection of the most stable conformer.
2. Draw a Newman Projection of the most stable conformer.
3. If a ${\mathbf{CH}}_{\mathbf{3}}\mathbf{-}{\mathbf{CH}}_{\mathbf{3}}$ eclipsing interaction costs 11kJ/mol (2.5 kcal/mol) and a ${\mathbf{CH}}_{\mathbf{3}}\mathbf{-}{\mathbf{CH}}_{\mathbf{3}}$ gauche interaction costs 3.8kJ/mol (0.9 kcal/mol), make a quantitative plot of energy versus rotation about the C-2 C-3 bond.

Identify each pair of relationships among the groups in glucose (pink–blue, pink–dark blue, pink–black, blue–dark blue, blue-black, dark blue-black) as cis or trans.

Assign R or S configurations to the chirality centers in ascorbic acid (vitamin C).

Answer questions 6-39 taking all stereoisomers into account.

(a)

(b)

(c)

The heat of hydrogenation for allene (Problem 7-61) to yield propane is -295 kJ/mol, and the heat of hydrogenation for a typical monosubstituted alkene, such as propene, is -125 kJ/mol. Is allene more stable or less stable than you might expect for a diene? Explain.

Predict the products of the following polar reaction, a step in the citric acid cycle for food metabolism, by interpreting the flow of electrons indicated by the curved arrows:

List the masses of the parent ion and of several fragments you might expect to find in the mass spectrum of the following molecule:

The mass spectrum (a) and the infrared spectrum (b) of an unknown hydrocarbon are shown. Propose as many structures as you can.

The mass spectrum (a) and the infrared spectrum (b) of another unknown hydrocarbon are shown. Propose as many structures as you can.

4-Methyl-2-pentanone and 3-methylpentanal are isomers. Explain how you could tell them apart, both by mass spectrometry and by infrared spectroscopy.

Grignard reagents undergo a general and very useful reaction with ketones. Methylmagnesium bromide, for example, reacts with cyclohexanone to yield a product with the formula ${\mathbf{C}}_{\mathbf{7}}{\mathbf{H}}_{\mathbf{14}}\mathbf{O}$. What is the structure of this product if it has an IR absorption at $\mathbf{3400}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$?

Ketones undergo a reduction when treated with sodium borohydride, ${\mathbf{NaBH}}_{\mathbf{4}}$. What is the structure of the compound produced by reaction  of 2-butanone with ${\mathbf{NaBH}}_{\mathbf{4}}$  if it has an IR absorption at $\mathbf{3400}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ and ${\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{74}$ in the mass spectrum?

Nitriles,  $\mathbf{R}\mathbf{-}\mathbf{C}\equiv \mathbf{N}$, undergo a hydrolysis reaction when heated with aqueous acid. What is the structure of the compound produced by hydrolysis of propanenitrile, ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{C}\equiv \mathbf{N}$, if it has IR absorptions from $\mathbf{2500}\mathbf{-}\mathbf{3100}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ and at $\mathbf{1710}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$, and has ${\mathbf{M}}^{\mathbf{+}}\mathbf{=}\mathbf{74}$?

The infrared spectrum of the compound with the mass spectrum shown below lacks any significant absorption above  $\mathbf{3000}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$. There is a prominent peak near $\mathbf{1740}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$ and another strong peak near $\mathbf{1200}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$.

Propose a structure consistent with the data.

The infrared spectrum of the compound with the mass spectrum shown below has a medium-intensity peak at about $\mathbf{1650}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$. There is also a C-H out-of-plane bending peak near $\mathbf{880}{\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$. Propose a structure consistent with the data.

Question: What alkyl halides would you use to prepare the following ketones by an acetoacetic ester synthesis?

Beginning with acetylene and any alkyl halide needed, how would you synthesize the following compounds?

(a) Decane

(b) 2,2-Dimethylhexane

(c) Hexanal 

(d) 2-Heptanone

Show how you could prepare the following compounds from 4-methyl-3- penten-2-one, ${\left({\mathbf{CH}}_{\mathbf{3}}\right)}_{\mathbf{2}}\mathbf{C}\mathbf{=}{\mathbf{CHCOCH}}_{\mathbf{3}}$

(a)

(b)

(c)

Question: Why do you suppose accidental overlap of signals is much more common in ¹H NMR than in ¹³C NMR?

Question: Which of the following compounds cannot be prepared by an acetoacetic ester synthesis? Explain.

(a) Phenylacetone

(b) Acetophenone 

(c) 3,3-Dimethyl-2-butanone

Name the following alkynes, and predict the products of their reaction

With:

 (1)  ${\mathbf{H}}_{\mathbf{2}}$in the presence of a Lindlar’s catalyst

 (2)  ${\mathbf{H}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}$in the presence of ${\mathbf{H}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$

From what alkyne might each of the following substances have been made? (Green = Cl.)

How would you prepare the following substances, starting from any

compounds having four carbons or fewer?

How would you prepare 1-phenyl-2-butanone, C₆H₅CH₂COCH₂CH₃, from benzyl bromide, C₆H₅CH₂Br? More than one step is required?

$\mathbf{\beta }$-Carotene, a yellow food-coloring agent and dietary source of vitamin A can be prepared by a double Wittig reaction between 2 equivalents of $\mathbf{\beta }$-ionylideneacetaldehyde and a diylide. Show the structure of the $\mathbf{\beta }$-carotene product.

For a given hydrogen atom to be acidic, the C-H bond must be parallel to the p orbitals of the CO double bond (that is, perpendicular to the plane of the adjacent carbonyl group). Identify the most acidic hydrogen atom in the conformation shown for the following structure. Is it axial or equatorial?

The following carboxylic acid can't be prepared from an alkyl halide by either the nitrile hydrolysis route or the Grignard carboxylation route.Explain.

Assuming that strong acids add to alkynes in the same manner as they add to alkenes, propose a mechanism for each of the following reactions:

Fill in the multiple bonds in the following model of naphthalene, ${\mathbf{C}}_{\mathbf{10}}{\mathbf{H}}_{\mathbf{8}}$ (gray 5 C, ivory 5 H). How many resonance structures does naphthalene have? Draw them.

The mercury-catalyzed hydration of alkynes involves the formation of an organomercury enol intermediate. Draw the electron-pushing mechanism to show how each of the following intermediates is formed.

Assign R or S stereochemistry to the two chirality centers in isocitrate, and tell whether OH and H add to the Si face or the Re face of the double bond.

The following model is a representation of ibuprofen, a common over-the-counter pain reliever. Indicate the positions of the multiple bonds, and draw a skeletal structure (gray 5 C, red 5 O, ivory 5 H).

Predict the product(s) and show the complete electron-pushing mechanism for each of the following dissolving metal reductions.

Rank the compounds in each of the following sets in order of their expected reactivity toward nucleophilic acyl substitution:

The following synthetic routes are incorrect. What is wrong with each?

Attempted Grignard reaction of cyclohexanone with tert-butyl magnesium bromide yields only about 1% of the expected addition product along with 99% unreacted cyclohexanone. If D₃O⁺ is added to the reaction mixture after a suitable period, however, the “unreacted” cyclohexanone is found to have one deuterium atom incorporated into it. Explain.

As far back as the 16th century, South American Incas chewed the leaves of the coca bush, Erythroxylon coca, to combat fatigue. Chemical studies of Erythroxylon coca by Friedrich Wohler in 1862 resulted in the discovery of cocaine, C₁₇H₂₁NO₄, as the active component. Basic hydrolysis of cocaine leads to methanol, benzoic acid, and another compound called ecgonine, C₉H₁₅NO₃. Oxidation of ecgonine with CrO3 yields a keto acid that readily loses CO₂ on heating, giving tropinone.

(a) What is a likely structure for the keto acid? 

(b) What is a likely structure for ecgonine, neglecting stereochemistry? 

(c) What is a likely structure for cocaine, neglecting stereochemistry?

Using curved arrows to indicate the electron flow in each step, show how the base-catalyzed retro-aldol reaction of 4-hydroxy-4-methyl-2-pentanone takes place to yield 2 equivalents of acetone.

Predict the product and provide the complete electron-pushing mechanism for the following two-step synthetic processes:

Where would you expect each of the following compounds to absorb in the IR spectrum?

(a) 4-Penten-2-one (b) 3-Penten-2-one

(c) 2,2-Dimethylcyclopentanone (d) m-Chlorobenzaldehyde

(e) 3-Cyclohexenone (f) 2-Hexenal

Predict the product (s) and provide the mechanism for each reaction below.

Reaction of acetone with ${\mathbf{D}}_{\mathbf{3}}{\mathbf{O}}^{\mathbf{+}}$ yields hexadeuterioacetone. That is, all the hydrogens in acetone are exchanged for deuterium. Review the mechanism of mercuric-ion-catalyzed alkyne hydration, and then propose a mechanism for this deuterium incorporation.

Nonconjugated $\mathit{\beta }$,$\mathit{\gamma }$-unsaturated ketones, such as 3-cyclohexenone, are in an acid-catalyzed equilibrium with their conjugated $\mathit{\alpha }$,$\mathit{\beta }$-unsaturated isomers. Propose a mechanism for this isomerization.

Nitriles can be converted directly to esters by the Pinner reaction, which first produces an iminoester salt that is isolated and then treated with water to give the final product. Propose a mechanism for the Pinner reaction using curved arrows to show the flow of electrons at each step.

Predict the products for the reactions in Problem 8-26 if each were run in DMSO with water. Show the complete mechanism including appropriate regiochemistry and stereochemistry.