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CHEM 335

Terms in this set (50)

Which of the following statements are TRUE concerning this laboratory exercise - The systematic identification of an organic compound?

In a "real world" situation, the compound could be one of several million possible known organic compounds

Your unknown may be a solid, liquid, or gas.

Your compound will contain at least C, H, and oxygen and one or more of several possible elements such as N, one or more halogens, S and Se.

You can use spectroscopic results to indicate the appropriate chemical tests to perform

Your compound, when you analyze it, may be impure, ie, a component of a mixture
TRUE: In a "real world" situation, the compound could be one of several million possible known organic compounds

FALSE: Your unknown may be a solid, liquid, or gas.

FALSE: Your compound will contain at least C, H, and oxygen and one or more of several possible elements such as N, one or more halogens, S and Se.

FALSE: You can use spectroscopic results to indicate the appropriate chemical tests to perform

FALSE: Your compound, when you analyze it, may be impure, ie, a component of a mixture
A positive test with 2,4 dinitrophenylhydrazine could indicate the presence of which of the following function groups?

alkenes
amines
carboxylic acids
ketones
alcohols
ketones
Which classification test is used to tell apart (differentiate) an aldehyde from a ketone?

acetyl chloride test

bicarbonate test

chromic acid test

bromine test

2,4-dinitrophenylhydrazine (DNPH) test
chromic acid test
The compound shown will give clues to its structure by which of the following spectral features? (Assume there is no magnetic coupling with the aldehyde proton)

A sharp singlet in the region of delta=3.5 ppm (NMR)

An important pair of moderately strong absorptions at about 800. and 900 wavenumbers IR)

A triplet at about delta = 2.2 ppm, integrating for 2 protons (NMR)

A strong, sharp absorption at about 1730 wavenumbers (IR)

A strong, broad absorption at about 3300 wavenumbers (IR)
FALSE: A sharp singlet in the region of delta=3.5 ppm (NMR)

FALSE: An important pair of moderately strong absorptions at about 800. and 900 wavenumbers IR)

TRUE: A triplet at about delta = 2.2 ppm, integrating for 2 protons (NMR)

TRUE: A strong, sharp absorption at about 1730 wavenumbers (IR)

FALSE: A strong, broad absorption at about 3300 wavenumbers (IR)
Which of the following reagents would give positive tests for the following molecule? (an ketone with and has a bromine)

Bromine in carbon tetrachloride

2,4-dinitrophenylhydrazine

acetyl chloride

chromic acid - Jones reagent

potassium permangeate
TRUE: Bromine in carbon tetrachloride

TRUE: 2,4-dinitrophenylhydrazine

FALSE: acetyl chloride

FALSE: chromic acid - Jones reagent

TRUE: potassium permangeate
A reflux setup allows for heating a chemical reaction for a given amount of time, while continually condensing the vapors produced back into the original flask using a condenser. Which of the following statements are TRUE/FALSE about reflux technique as applied in an organic chemistry laboratory?

If you are to reflux a reaction for a certain time period (e.g, "reflux for 45 minutes"), the time period should begin from when the heat source is turned on
FALSE
A reflux setup allows for heating a chemical reaction for a given amount of time, while continually condensing the vapors produced back into the original flask using a condenser. Which of the following statements are TRUE/FALSE about reflux technique as applied in an organic chemistry laboratory?

In a reflux setup, solvent vapors are trapped by the condenser, and the concentration of reactants remains constant throughout the process
TRUE
A reflux setup allows for heating a chemical reaction for a given amount of time, while continually condensing the vapors produced back into the original flask using a condenser. Which of the following statements are TRUE/FALSE about reflux technique as applied in an organic chemistry laboratory?

During a reflux the boiling rate should be controlled such that the "reflux ring" (the upper limit of where hot vapors are actively condensing) is maintained roughly one-third of the way up the condenser
TRUE
A reflux setup allows for heating a chemical reaction for a given amount of time, while continually condensing the vapors produced back into the original flask using a condenser. Which of the following statements are TRUE/FALSE about reflux technique as applied in an organic chemistry laboratory?

Since refluxing involves heating material - mostly to solvent's boiling temperature - one should add appropriate smooth boiling devices to control bumping
TRUE
A reflux setup allows for heating a chemical reaction for a given amount of time, while continually condensing the vapors produced back into the original flask using a condenser. Which of the following statements are TRUE/FALSE about reflux technique as applied in an organic chemistry laboratory?

Reflux technique is only applied to chemical reactions involving volatile material or solvents.
FALSE
In this lab, you will be using a separatory funnel and it is very important for you to understand what chemicals each layer in the funnel contains, and to know which layer is the aqueous layer and which is the organic layer. Which layer contains the majority of the product (the acetate ester) in this lab?

The organic layer, which is the upper layer

the aqueous layer, which is the upper layer

the organic layer, which could be either upper or lower layer. You must test each layer while doing the experiment

The aqueous layer, which could be either upper or lower layer. You must test each layer while doing the experiment

The organic layer, which is the lower layer
the organic layer, which could be either upper or lower layer. You must test each layer while doing the experiment
An orgo lab student wanted to synthesize an isoamyl acetate ester. Using reflux technique, the student heated 7.50 grams of isoamyl alcohol (3-methyl-1-butanol) with 22.5 grams of acetic acid (ethanoic acid) and 4.50 grams of sulfuric acid to prepare the ester. Based on these numbers, how many grams of isoamyl acetate should the student theoretically obtain? (molecular weights: isoamyl alcohol=88.15, acetic acid=60.05, sulfuric acid=90.08, isoamyl acetate=130.19)
7.5g/88.15= 0.085 mol of isoamyl alcohol

grams of isoamyl acetate: 0.085mol*130.19=11.07 grams
Suppose that in the synthesis of isoamyl acetate, a student began with 6.144 grams of acetic acid and 3.819 grams of isoamyl alcohol. If the mass of isoamyl acetate obtained were 4.925, what was the percent yield?
acetic acid: 6.144g/60.05=0.1023 mol

isoamyl alcohol: 3.819g/88.15=0.0433 mol (theoretical mol)

isoamyl acetate:
4.925g/130.19=0.03783 mol (experimental mol)

(.03783/0.0433)*100%= 87.37%
Various chemicals are used in this procedure, and it is important that we the purpose of each. What is the reason for using magnesium or sodium sulfate?

It shifts the equilibrium to the right to favor the product

it is a catalyst

it is a drying reagent used to dry the product

it removes the acetic acid

it aids in expelling the carbon dioxide

it is used in excess to ensure the equilibrium favors the product
It is a drying agent used to dry the product.
A Fisher esterification is performed with methanol and benzoic acid. All the oxygen atoms of the methanol are isotopically labelled oxygen-18 atoms, and none of the oxygen atoms of the benzoic acid are oxygen-18, i.e. in the benzoic acid all the oxygens are oxygen-16. Which of the following products would you expect from this reaction?
Methyl benzoate, with the ether oxygen being oxygen-18
Joe, an orgo lab student, wants to synthesize benzyl butyrate by Fischer esterification method in the lab. Which starting reagents should the students choose for this synthesis?

1-propanol and 2-phenylacetic acid

benzyl alcohol and 2-phenylacetic acid

benzyl alcohol and butyric acid

1-propanol and benzoic acid
benzyl alcohol and butryic acid
Below are several types of light. Put them in order from short wavelength to long wavelength.
X-rays are shorter than ultraviolet light waves which are shorter than visible light waves which are shorter than infrared light waves
Which of the following statements about the ordinary IR spectroscopic regions are TRUE?

We can sense some of the frequencies of the fundamental region of the IR as heat

In general, the IR fundamental region has a longer wavelength region than the region we call the x-ray region

ordinarily, we sense most IR frequencies as colors in the region we call red

In general, radio frequencies are higher wavenumbers of 250 inverse cm

An IR wavelength of 40 microns corresponds to a wavenumber of 250 inverse cm
True: We can sense some of the frequencies of the FUNDAMENTAL region of the IR as heat

True: In general, the IR FUNDAMENTAL region has a longer wavelength region than the region we call the x-ray region.

True: An IR wavelength of 40 microns corresponds to a wavenumber of 250 inverse cm
What is the wavenumber of IR radiation designated by 28.79 microns?
(1/28.79*10^-4)=347
Which of the following events may occur when IR radiation is absorbed?

More intense IR absorptions occur for those bonds having greater dipole moment changes with bond lengthening in vibration

Non-bonding electrons are promoted to higher energy molecular orbitals

relative inter-atomic rotational orientations are changed

chemical bonds are broken

intra-molecular bond angles are changed
True: More intense IR absorptions occur for those bonds having greater dipole moment changes with bond lengthening in a vibration.

True: Intra-molecular bond angles are changed.
Which of the following groups MAY have no detectable IR absorption in the range usually associated with an absorption?

iso-cyanate

ether C-O bond

C-C bond

ketone C=C=O bonds

ketone carbonyl
True: C-C
Match each of the functional groups with the appropriate general infrared absorption location in wavenumbers.

A: Ketones/Aldehydes
B: Alkanes
C: Alkenes
D: Ethers
E: Alcohols
F: Alkynes
A: Ketones/Aldehydes: 1725

B: Alkanes: 3000

C: Alkenes: 1640

D: Ethers: 1200

E: Alcohols: 3300

F: Alkynes: 2200
Consider the following statements as they apply to infrared spectroscopy. Decide if each is true or false.
True: Absorption bands in infrared spectroscopy are due to vibrational and rotational-vibrational transitions in molecules.

True: For a vibrational mode to be infrared active, the vibration must cause a change in the dipole moment of the molecule.

True: Because gas molecules are free to rotate, rotational-vibrational transitions can be observed in their infrared spectra. For this reason at high resolution, a gas phase spectrum is characterized by many sharp lines.

False: For a given pair of atoms, the vibrational frequency expected if they are joined by a single bond should be higher than if they are joined by a double bond.

True: The quantized nature of molecular vibrations are generally understood in terms of a simple harmonic oscillator model.
Consider the following statements as they apply to infrared spectroscopy. Decide if each is true or false.
True: In dipersive infrared spectroscopy, the source radiation is dispersed by use of a diffraction grating.

True: Sample holders and optics for infrared spectroscopy are typically made of NaCl or KBr which is transparent to most infrared wavelengths.

True: The most common pyroelectric detector in FTIR is deuterated triglycine sulfate (DTGS).

False: A common source for infrared spectroscopy is a deuterium lamp.

True: Most FTIR spectrometers utilize a Michelson interferometer.
What is the SODAR of a molecule with 13 carbon atoms, 22 hydrogen atoms, and 3 oxygen atoms?
3
Consider the following statements regarding NMR spectroscopy. Determine whether each each statement is true or false.
False: A typical value for the chemical shift of methyl protons is 5.0.

False: NMR spectroscopy can be applied only to molecules containing protons.

False: Spin-spin splitting can occur over many bond lengths in a molecule.

True: The twelve equivalent protons in TMS are highly shielded and therefore provide a convenient proton reference point in NMR spectroscopy.
Name a compound with the formula, C2H6O, which will show only one peak in the NMR spectrum. Use the common name of this compound
dimethyl ether
Match each lettered statement to the corresponding feature of an NMR spectrum.

A: The number of adjacent, coupled nucleii.

B: The number of nucleii in the molecule with non-zero I values.

C: The nature of the chemical environment for each different group of nucleii.

D: The number of chemically non-equivalent nucleii.

E: The relative number of nucleii responsible for each peak.
Chemical shifts: The nature of the chemical environment for each different group of nucleii

Peak multiplicities: The number of adjacent, coupled nucleii

Relative integrated signal intensities: The relative number of nucleii responsible for each peak

Number of signals: The number of chemically non-equivalent nucleii
Consider the following statements regarding NMR spectroscopy. Determine whether each each statement is true or false
True: The TMS protons are highly shielded and appear upfield of other organic protons in an NMR spectrum.

False: A typical value for the chemical shift of aromatic protons is 4.0.

True: Spin-spin splitting arises from interactions of one proton with a neighboring nucleus.

True: NMR spectroscopy can be applied to molecules containing protons, 13C, or 19F.
TLC analysis requires microgram quantities of sample for an effective analysis. Spotting too much sample or having too broad a sample spot on the plate causes streaking which compromises the accuracy of your analysis.
true
If the mobile phase in a TLC analysis is less polar than the stationary phase the solutes/compounds will migrate faster up the plate.
false
A filter paper is placed in the developing jar to ensure that solvent equilibration within the chamber is maintained.
true
Chromatography techniques are based on the differential partitioning of components between a stationary phase and mobile phase.
true
Visualization of spots/compounds on the TLC plate under UV light is only applicable to compounds that absorb light in the same wavelength region as UV light in use.
true
For TLC analysis of cinnamic acid and 2-Methyl-1-phenyl-1-propene using ethyl acetate solvent, it is expected, after development, that the cinnamic acid spot will be approximately ~ 2 cm above the 2-Methyl-1-phenyl-1-propene spot.
false
In thin-layer chromatography (TLC) the mobile phase travels up the TLC plate - adsorbent layer coated onto an appropriate support- by capillary action carrying with it the solute spot..
true
In TLC plate development, the eluting solvent level in the chamber should be above the index mark (the line of initial spot) on the TLC plate.
false
...
True: To monitor the progress of a reaction.

False: To identify compounds based on their Rf values.

True: To establish that two compounds are identical.

False: To determine the polarity of a compound by its Rf value.

True: To determine the number of compounds in a mixture.
The thin-layer chromatography (TLC) technique is used for both qualitative and quantitative analysis in organic chemistry laboratories. Which of the functions (applications) listed below apply to TLC technique?
False: Determination of optical rotation properties of compounds in a mixture.

True: Determination of purity of compounds and reagents in the lab

True: Monitoring the course of reaction progress by comparing the amount of product formed to the amount of corresponding reagents.

False: Determination of structural (constitutional) isomers present in a sample.
In chromatographic separations, components are partitioned between a mobile phase and a stationary phase based on differences in their partition (distribution) coefficients. Which of the following statement best define what a partition (distribution) coefficient is; Incorrect The equilibrium ratio of the concentration of a given component in vapor phase and liquid phase.
The equilibrium ratio of the concentrations of a given component in two phases at a particular temperature.
When it comes to visualization of spots on the TLC plate, which of the method(s) listed below are/is considered nondestructive. - Check all that apply
False: Using potassium permanganate ink.

False: Using 2,4 dinitrophenyl hydrazine reagents to visualize.

False: Staining with iodine vapors.

True: Visualization under ultraviolet light (254 nm)

False: Using phosphomolybdic Acid (PMA) /ethanol solution.

True: Direct visualization of colored compounds
In thin-layer chromatography (TLC) the choice of visualization technique is dependent on the compound being analyzed. Which of the below-listed visualization techniques would be appropriate for visualizing benzaldehyde on a TLC plate?
False: Iron (III) Chloride

False: Ninhydrin

True: UV Light

true: Phosphomolybdic Acid (PMA)

True: Potassium permanganate ink/stain

False: Bromocresol Green

True: 2,4 dinitro phenylhydrazine
Chromatography is a term describing a collection of laboratory techniques used to separate the components in a mixture PRIOR to the measuring their individual responses for quantitative analysis. What chromatographic technique will be used to separate the volatile impurities in the unknown whiskey products.
gas chromatography
Which types of properties may be exploited using gas chromatography?
True: Physical Properties

True: Chemical Properties

False: Basic Properties

False: Electronic Properties
The stationary phase in gas chromatography is best described as
is a thin liquid layer that is chemically bonded to the interior of a capillary column that comes in contact with an inert carrier gas or mobile phase
In gas chromatography, the stationary phase is made up of high molecular weight non-volatile polymer coated on solid support packed inside a column and the mobile phase is an inert gas that carries the volatilized components of the sample mixture through the column toward the detector. The physical form of the stationary (s) and mobile phase (m) in gas chromatography are:
liquid (s), gas (m)
Which of the following factors determine the degree of separation of components in gas chromatography?
True: Volatility of the components in the mixture.

False: The molecular weight of the components in the mixture.

True: The polarity of the components in the mixture.

True: The amount or concentration of components in the mixture.
Identify the statements about chromatography as true or false.
True: For two components to be separated sharply they must have significantly different retention times or retention factors.

False: In thin-layer chromatography and gas (vapor phase) chromatography the separation of components in the mixture is temperature-dependent.

False: In all chromatographic separations, components in a mixture are distributed between a solid stationary phase and a liquid mobile phase.

False: In gas chromatography, a polar stationary phase will attract polar components more strongly consequently reducing the component's retention times.
Predict which of the following compounds will generate the largest detector response per unit concentration. Assume the concentration of each compound is the same in the sample mixture analyzed by GC-FID.
2-methyl-1-butanol
Consider the following statements as they apply to gas chromatography. Decide if each is true or false.
True: Organic compounds are ionized in an FID; this results in a measurable current that is roughly proportional to number of reduced carbon atoms in the flame.

False: The injection port temperature should be set at the average boiling point of all analytes.

False: A column temperature about 50 °C below the average boiling point of the sample components results in a reasonable elution time.

True: The technique referred to as �gas chromatography� is actually gas-liquid chromatography since the stationary phase is a liquid adsorbed on the surface of an inert solid.

False: A TCD is insensitive to non-combustible gases such as water and carbon dioxide.
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