CHEM 237 - Organic Chemistry Lab Final TAMU

Separation by liquid-liquid extraction is based on

a) compound's dielectric constant in 2 dif solvents

b) # of theoretical plates in the separation

c) use of phase transfer catalysts

d) difference in boiling points of 2 liquids

e) distribution of a compound between 2 immiscible phases

e) Distribution of a compound between two immiscible phases.

Preparative gas chromatography is often chosen over distillation as a means of separation because gas chromatography

a) is relatively inexpensive

b) does not require thermally stable compounds

c) can separate some compounds with identical boiling points

d) will allow large quantities of sample to be injected

e) does not require that compounds be volatile to be separated

c) Can separate some compounds with identical boiling points

In the Phase Transfer Catalysis experiment (10), a general form of quaternary ammonium salt is R4N+X. The R4N+, where R is an alkyl chain, can be in both the aqueous (polar) and organic (nonpolar) phase because [choose as many as apply]

I) R4N+ is a charged species that can dissolve in the aqueous pase

II) R4N+ is a charged species that can dissolve in the organic phase

III) R is a hydrocarbon chain that can dissolve in the aqueous phase

IV) R is a hydrocarbon chain that can dissolve in the organic phase

I) R4N+ is a charged species (polar) and charged species can dissolve in the aqueous phase.

IV) R is a hydrocarbon chain (nonpolar) and hydrocarbon chains can dissolve in the organic phase.

Like dissolves like.

What be an undesirable property for a recrystallization solvent? The solvent would

a) dissolve no impurities, even at high temperatures

b) dissolve the product to be isolated at all temperatures

c) dissolve the product to be isolated at high but not at low temps

d) have a low freezing point

e) be nontoxic

b) dissolve the product at all temps

Absorption of energy in the infrared spectrum produces changes in

a) molecular vibes

b) bond angles

c) dipole moments

d) bond length

e) all

e) all

Gas chromatographs usually contain a column which is packed w/a solid support and a liquid stationary phase. Separation occurs when

a) your sample moves by capillary action through the column and interacts with the stationary phase

b) your sample is carried through the column by a low boiling solvent

c) the carrier gas takes your sample through the column w/o separating

d) the carrier gas carries your sample through the column, where it interacts with the stationary phase and the sample components are separated

e) your sample was separated between the ether and water layer

d) the carrier gas carries your sample through the column, where it interacts with the stationary phase and the sample components are separated

Which of the following qualitative tests could be used to distinguish between limonene and eugenol?

a) ferric chloride test

b) iodoform test

c) bromine test

d) baeyer test

e) silver nitrate test

a) ferric chloride

Which of the following alcohols undergoes dehydration reaction (E1) most rapidly?

a) 2-methyl-2-butanol

b) 2-pentanol

c) 3-pentanol

d) 1-pentanol

e) none, all of these have formula C5H12O and undergo dehydration at the same rate

a) 2-methyl-2-butanol

You are given a DCM solution with compounds A, B, and C. First extract with 3N NaOH, only a salt of A is in the aqueous layer. Re-extract organic layer with 3N HCl, only C in organic layer. Compound A is probably

a) hexane

b) benzoic acid

c) naphthalene

d) sodium sulfate

e) benzocaine

b) benzoic acid

Which is true of molecular mechanics?

a) employs ab initio methods to calculate strain energies

b) treats chemical bonds as mechanical springs

c) doesn't follow Hooke's Law

d) requires cray super computers to do simple calculations

e) all

b) treats chemical bonds as mechanical springs

Which is NOT a requirement for prep gas chromatography?

a) sample must be volatile

b) sample must be dry

c) sample must be thermally stable

d) sample size must be less than 5 microliters

e) all

d) sample size must be less than 5 microliters

Reaction of naphtholate anion and allyl bromide involved a catalyst (tri-n-butyl ammonium chloride). The catalyst carries

a) the water soluble naphtholate anion into the organic phase

b) the hydrophobic naphtholate anion into the aqueous phase

c) the water soluble allyl bromide into the organic phase

d) the hydrophobic allyl bromide into the aqueous phase

a) the water soluble naphtholate anion into the organic phase

In an SN1 solvolysis rxn such as the one in lab

a) the rate of rxn is dependent on rate of addition of NaOH

b) rate constant, k, would 2X if alkyl halide amount was 2X

c) rxn rate accelerated by use of a more polar solvent

d) rate constant would be 0 if rxn mixtures weren't stirred

e) rate constant would be decreased if NaOH wasn't added to neutralize acid

c) rxn rate accelerated by use of a more polar solvent

Tertiary alcohols reacting with sodium hypochlorite (NaClO) yield

a) ketones

b) carboxylic acids

c) aldehydes

d) amides

e) none

e) none

Spilled nitric acid/sulfuric acid on you. What do you do? Wash it with

a) water and apply 0.6 M sodium thiosulfate solution

b) water and apply 0.6 M potassium permanganate solution

c) cold water and apply 0.6 M sodium bicarbonate solution

d) 0.6 M sodium hydroxide solution

e) 0.6 M boric acid

c) cold water and apply 0.6 M sodium bicarbonate solution

Why do you allow a hot recrystallizing solution to cool slowly?

a) quickly forms large crystals, trapping impure solution

b) quickly forms small crystals, adsorbing impurities

c) quickly may induce undesirable reactions

d) quickly causes impurities to oil out, making it impossible to crystallize

e) statement is false, quick cooling is correct

b) quickly forms small crystals, adsorbing impurities

Butyl Butyrate, an ester, differs from p-dioxane, an ether, by showing strong infrared absorbance at

a) 3500 1/cm

b) 2950 1/cm

c) 2250 1/cm

d) 1745 1/cm

e) 1212 1/cm

d) 1745 1/cm

Simple distillation is most effective in separating compounds with

a) almost identical boiling points

b) greatly different densities

c) widely different boiling points

d) different colors

e) different Rf values

c) widely different boiling points

Which is NOT true of melting point

a) its the temp where liquid and solid exist in equilibrium

b) it gives indication of compound purity

c) if a new compound is made, melting point can identify it

d) can tentatively id a known compound

e) low purity is associated with a broad melting range

c) if a new compound is made, melting point can identify it

Rf value is

a) distance of solvent from application / distance solute travels from application

b) distance solute from application / distance solvent from application

c) distance solute from edge of plate / distance solvent from edge of plate

d) distance solvent from edge / distance solute from edge

e) distance solute A / distance solute B

b) distance solute from application / distance solvent from application

Eugenol and limonene

a) are an acetogenin and a terpene respectively

b) are a terpene and an acetogenin respectively

c) are natural products

d) a and c

e) b and c

d) eugenol is an acetogenin, limonene is a turpene, they're both natural products

Name of mechanism of acid catalyzed dehydration of cyclohexanol?

a) SN1

b) SN2

c) E1

d) E2

e) E1cB

c) E1

which is NOT a desirable characteristic of an extraction solvent? The solvent should

a) be immiscible with the solvent of the solution

b) have the most favorable distribution coefficient for the component to be separated, and unfavorable for other components

c) not react chemically with mixture components

d) be readily separated from the solute

e) be nonvolatile

e) be nonvolatile

When performing prep gc, the collection tube must be

a) capped while collecting to avoid loss of volatile solute

b) capped while collecting to avoid contamination

c)capped while collecting to avoid absorption of water by the sample, which would ruin the IR spectrum

d) uncapped to allow free passage of vapor through tube

e) maintained in a downward slope to keep the GC port from plugging up

d) uncapped to allow free passage of vapor through tube

During the purification of allyl-2-napthyl ether in the phase transfer catalysis experiment, some products were retained in the silica gel column. What is the nature of these products?

a) polar

b) nonpolar

c) acidic

d) basic

e) none

a) polar

Rxn of 1-chloro-1-phenylethane with water

a) is a first order rxn

b) involves the slow ionization of carbon-chlorine bond to form a carbocation

c) is an SN2 rxn

d) a and b

e) a, b, c

d) is a first order rxn and involves the slow ionization of carbon-chlorine bond to form a carbocation

When analyzing the IR of the product from the Oxidation of a Secondary Alcohol experiment (12) you were looking for what in the spectra?

a) disappearance of a peak at apx 1700 1/cm and appearance of broad peak at apx 3300 1/cm

b) appearance of a peak at apx 1700 1/cm and disappearance of broad peak at apx 3300 1/cm

c) appearance of a strong peak at apx 2200 1/cm and disappearance of strong peak at apx 1700 1/cm

d) disappearance of a strong peak at apx 2200 1/cm and appearance of strong peak at apx 1700 1/cm

e) None

b) appearance of a peak at apx 1700 1/cm and disappearance of broad peak at apx 3300 1/cm

Why do you add boiling chips to a solution?

a) to keep the solution homogenous

b) to increase the rate of reflux

c) to promote even boiling

d) to lower the boiling point

e) all

c) to promote even boiling

Which is NOT a characteristic of an ideal solvent for recrystallization?

a) inexpensive

b) nontoxic

c) dissolves a large amount of the material to be crystallized at high temperatures

d) nonvolatile

e) doesn't react with material being recrystallized

d) nonvolatile

A strong IR absorbance in the 1670-1830 1/cm range is present for [choose as many as apply]

a) alkenes

b) esters

c) aldehydes

d) carboxylic acids

e) alcohols

b) esters

c) aldehydes

d) carboxylic acids

In performing simple distillation

a) better to distill rapidly

b) higher boiling compound distills first

c) temp should be held below 100C

d) 2 compounds can be separated completely if they have boiling point difference less than 10C

e) the distillate of a mixture contains a progressively larger percentage of the lower boiling compound as the distillation proceeds

e) the distillate of a mixture contains a progressively larger percentage of the lower boiling compound as the distillation proceeds

Normally a mix of two dif solid compounds will melt over a broader range than either pure solid. However they will show a sharp melting point if

a) theyre diastereomers

b) one solid melts with decomposition

c) they have the same melting point

d) they form an azeotrope

e)they form a eutectic

e)they form a eutectic

In TLC, the Rf will change when any of the following parameters change EXCEPT

a) the solvent

b) the functionality of the compound

c) the absorbent

d) the level of saturation of the developing chamber with solvent vapors

e) the distance traveled by the solvent front

e) the distance traveled by the solvent front

What kind of technique did you use to obtain water insoluble oils like limonene from natural sources?

a) steam distillation

b) GC

c) Simple distialltion

d) TLC

e) Extraction

a) steam distillation

What is the predicted hybridization of the oxygen in ethanol

a) sp

b)sp2

c) sp3

d) s

e) none

c) sp3

Which of the following C-C-C-C dihedral angles was calculated for the butane conformer of lowest energy?

a) 0

b) 60

c) 65

d) 120

e) 180

e) 180

The compound which would be most soluble in aqueous HCL is

a) C6H5-C6H4-OH

b) C6H5-CH2-COOH

c) (CH3)3CH

d) C6H5-CH2-Cl

e) C6H5-CH2-NH2

e) C6H5-CH2-NH2

Which of the following is an effective means to increase separation between two peaks (increase resolution) on the GC spectrum

a) increase carrier gas flow rate

b) increase column temp

c) decrease stationary phase thickness

d) inject sample more slowly

e) increase length of column

e) increase length of column

Carrying out the solvolysis of 1-chlor-1-phenylethane in 80:20 water:ethanol rather than 50:50 water:ethanol will

a)increase rate of reaction

b)decrease rate of reaction

c) change mechanism of reaction from Sn1 to Sn2

d) leave rate unchanged

e) cause the reaction to yield mainly 1-ethoxy-1-phenylethane

a)increase rate of reaction

Recrystallization is best at purifying compounds that are

a) gases

b) liquids

c) completely insoluble in a solvent at all temps

d) much more soluble at increased temp

e) similar in solubility to their impurities

d) much more soluble at increased temp

The 2 characteristics of a bond that affect the frequency of infrared radiation absorbed by that bond are

a) size of atom and number of atoms

b) size of atom and bond strength

c) molecular weight and bond strength

d) number of atoms and molecular weight

e) none

b) size of atom and bond strength

Butanol (bp 117C) and water (bp 100C) form an azeotrope (bp 92.7C) which is 90% butanol and 10% water by volume. You are distilling a mixture containing 125 mL butanol and 10 mL water. which is true?

a) the water would distill first, then the butanol

b) the azeotrope would distill first, followed by excess butanol

c) the azeotrope would distill first followed by excess water

d) all of the solution would distill as the azeotrope

e)excess butanol would distill first, followed by the azeotrope

b) the azeotrope would distill first, followed by excess butanol

Compounds A and B both have melting points of 140C. If A is mixed with B at a ratio which leads to melting at the eutectic point, the melting point of the mixture

a) will remain at 140C

b) will be less than 140C

c) will be greater than 140C

d) will contain 2 separate melting points

e) can't be determined

b) will be less than 140C

The movement of the liquid mobile phase in TLC is caused by

a) a pressure differential

b) gravity

c) adsorption

d) capillary action

e) vapor pressure

d) capillary action