Synthesis Lab Exam

Which is considered NOT a good scientific laboratory notebook practice?

• writing in pencil

Which is considered a good scientific laboratory notebook practice?

• using a table of contents

• marking out unused space in ink

• writing the reaction for the experiment being performed

What is the purpose of a lab notebook?

• It is a written record of procedures, data, observations, results, thoughts

• It may serve as knowledge for future researchers.

• It is a legal document used to defend intellectual property

What peaks at ~1750 cm^-1

Carbonyl group (C=O)

What peaks at 3000-3500 cm^-1

Alcohol group (-OH)

What peaks at 1050-1250 cm^-1

Single bond to anything but C-H

What are the units of wavenumber in infrared spectroscopy?

cm^-1

Review ^1 H NMR

Number of H + 1 is the splitting of the signal (siglet, doublet…)

Review ^13 C NMR

Symmetry means less Carbon signals

If you spill a chemical on yourself, you should

-Wipe and rinse immediately for 15 minutes

If you spill a chemical on yourself, DO NOT

-React with another chemical to neutralize it

-Wipe and rinse with acetone

-Dry off with nitrogen air

What is the chemical-labelled pictogram for flammable?

Fire

What is the chemical-labelled pictogram for toxic?

skull and bones

What is the chemical-labelled pictogram for oxidizer?

circle with flames behind it

In preparation for conducting an acid-base extraction, you want to dissolve your
mixture in an organic solvent first. Which solvent would NOT be an appropriate choice?

ethanol

In preparation for conducting an acid-base extraction, you want to dissolve your
mixture in an organic solvent first. Which solvent would be an appropriate choice?

hexane

dichloromethane

diethyl ether

When separating a mixture of a octanoic acid and octane, what is the key step to separating the two compounds using extraction?

Deprotonation of the octanoic acid with a base

Why is steel wool or glass prongs used in a fractional distillation column?

 

It is increases the surface area and improves the separation between liquids

What is the effect on the observed temperature reading if the bulb of the thermometer at the head of the distillation apparatus is positioned above the opening of the condenser?

 

the reading of the boiling point will be low

The melting point of a pure compound is known to be 110-111 °C. If the compound
were contaminated with an impurity you could expect the melting point to be:

85-100 °C

larger range. lower numbers

How to take melting point

1. The first value recorded for the melting range is with the very first appearance of liquid.

2. The second value recorded for the melting range is with the melting of the entire sample, which occurs when all areas of opaque solid have turned into a transparent liquid.

Which of the following reagents could be used to remove impurities during recrystallization?

charcoal

Which of the following step may be attempted in order to initiate crystal formation of a saturated solution (containing your crude product) that has slowly cooled?

scratch the wall with a glass rod

A solution containing 0.2 g/mL of a pure R enantiomer in a 1 dm polarimeter rotates plane polarized light by +3°.  What is the specific rotation of the R isomer?

+15°

A pure sample of the R enantiomer of a compound has a specific rotation, [a], of +20°.  A solution containing 0.2 g/mL of a mixture of enantiomers rotates plane polarized light by -2° in a 1 dm polarimeter.  What is the enantiomeric excess (%ee) of the mixture?

50% S

Which of the following can easily separated through column chromatography using silica gel?

carotenoids

Why is it necessary to perform TLC analysis on the fractions that are collected from column chromatography?

To know why fractions can be combined

 

To match the Rf of the sample with the Rf of the product

 

To determine which fractions contain the product

You have a mixture of hexanol, hexanoic acid, and dodecane and perform TLC analysis on a silica gel plate (with an eluant mixture of 80:20 hexane:methanol). Which compound would should have the highest R_f value?  

dodecane

Which of the following is a non-destructive visualization technique used in TLC?

 

UV light

Which of the following is a destructive visualization technique used in TLC?

Ninhydrin

 

Sulfuric acid

 

Iodine

Which of the following would be an appropriate sentence in the experimental section of a scientific report?

The crude product was recrystallized from ethanol to give pure 2- nitroresorcinol (2.20g, 14.2mmol) as red, needle-like crystals.

Which of the following may NOT be considered proper technical writing convention?

 

Including lists of all equipment (including common glassware)

Which of the following may be considered proper technical writing convention?

Using leading zeros with number less than 1 (e.g. 0.25)

Referring to figures correctly in text

 

Avoiding bulleted lists

If the Grignard reagent, phenylmagnesium bromide, encounters water, what product is formed?

benzene

Two equivalent of a Grignard reagent can react with an ester to form a(n) ________ upon aqueous workup.

alcohol

Which carrier gas is commonly used in gas chromatography?

nitrogen

Why is the injector port heated on a GC?

 

To volatilize the sample