CHEM 2205 SP25 - Organic Lab Sample Exam Questions

Organic Chemistry Lab Exam Practice Questions

Which bonds have a stretching mode IR absorbance in the functional group region?

O-H and C-O bonds.

What spectroscopic method can distinguish 1,2,3-tribromobenzene from similar compounds?

Proton NMR spectrum.

What is indicated by peaks (a) and (b) collectively in the 1H-NMR spectrum?

An ethyl group on the molecule.

What feature in the proton NMR spectra of 3,3-dimethyl-1-butanol and n-butanol is expected to be significantly different?

The number of peaks in the spectrum, the integrals of peaks corresponding to C-H protons, the multiplicity of peaks corresponding to C-H protons, the chemical shift of the O-H proton peaks, and the multiplicity of the O-H proton peaks.

What is a potential disadvantage of fragmentation in mass spectrometry?

It can lead to mass spectra without a molecular ion peak.

What is the role of fragmentation in mass spectrometry?

It provides structural information but can also complicate spectra by removing the molecular ion peak.

Which reagents are suitable bases for initiating a protecting group reaction?

Sodium metal and Sodium carbonate.

Which changes would speed up a protecting group reaction?

Substituting 3-pentanone for acetone.

What characteristics are essential to a good protecting group?

It is easily applied and removed from the reactive site and is resistant to reaction conditions used to modify other sites, and can be removed under conditions that do not affect the rest of the compound.

In a reaction with two pathways, what product forms at progressively higher temperatures and longer times?

Product B, the thermodynamic product, will form in greater abundance as it is more stable.

When bromobenzene is nitrated, what is the major product indicated by the 1H NMR data?

Two doublets in the aromatic region suggests para and ortho substitution.

What are the activating/deactivating effects of halogens during electrophilic aromatic substitution?

Ortho-para directors which inductively deactivate the ring and sterically blocks the ortho position.

What is the role of sulfuric acid in nitration?

It acts as a catalyst, protonating nitric acid which decomposes into nitronium.

How can high conversion of benzoic acid to methyl benzoate be achieved during Fischer esterification?

Water was removed from the system as it formed which exploits LeChatlier’s principle.

How to increase the yield of hydrolyzing methyl benzoate to benzoic acid?

Using water as the solvent and running the reaction in a fractional still to remove methanol.

Why does saponification have a very high yield in traditional soap making?

Saponification is hydrolysis under basic conditions, which produces a carboxylate in the presence of an alcohol, making the reaction irreversible.

List techniques useful for exclusion of atmospheric moisture from a reaction.

Attaching a drying tube, using a stream of nitrogen pressure and an oil bubbler, using a Schlenk line, and running the reaction in a glove box.

List techniques that allow for transferring liquids from one flask to another without air/moisture exposure.

Using a Schlenk line and running the reaction in a glove box.

Which atmospheric exclusion technique is most suitable when using solid PCl5 that needs to be weighed?

Running the reaction in a glove box.

Method used to remove moisture from organic solvents before use in the lab

Drying over 3 Å molecular sieves.

What best describes the purpose of the slim glass stem on the side of an addition funnel?

It allows pressure in the reaction flask and head space to equilibrate, promoting proper flow of liquid from the funnel to the flask in a closed system.

Which compounds can be reacted with benzaldehyde in a base-catalyzed crossed aldol condensation?

Compounds with alpha hydrogens.

What products are expected in the mass spectrum of aldol condensation between neopentanal and 3-pentanone?

Peaks corresponding to the masses of the possible condensation products after dehydration.

How to ensure a desired reagent concentration is kept as low as possible during a reaction?

Slow, dropwise addition of that reagent to the reaction mixture and rapidly stirring the reaction mixture as the reagent is added.