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AA JW Science Review > KA Chemical Processes > Flashcards

KA Chemical Processes Flashcards

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1
Q

What is the formula for perchloric acid?

A

HClO4

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2
Q

What is the mobile phase in thin-layer chromatography?

A

Liquid.

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3
Q

Name this compound: SO32-

A

Sulfite

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4
Q

Describe the difference between alpha and beta anomers. How do they form? How do you tell them apart?

A

When the hydroxyl group of a a straight-chain sugar attacks the carbonyl carbon, it can attack from either of 2 directions, resulting in two possible diastereomers as products.

Alpha = trans to the last carbon in the sugar chain = pointing down (axial) in the chair diagram.

Beta = cis to the last carbon in the sugar chain = pointing up (equatorial) in the chair diagram.

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5
Q

Name 2 reasons why aldehydes are more reactive than ketones.

A
  1. The aldehyde carbonyl carbon is more partially positive, because the alkyl groups of a ketone are electron-donating.
  2. Steric hindrance at the ketone makes it more difficult for a reaction to occur.
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6
Q

Name this compound: CrO42-

A

Chromate

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7
Q

Explain the Strecker synthesis. What are the reagents and steps involved? What is the final product?

A

Start with NH3, KCN, and an aldehyde or ketone.

Step 1 - Acid-catalyzed attack on the aldehyde by NH3. This will form an imine.

Step 2 - Acid-catalyzed attack on the imine by CN-. This will form an alpha amino nitrile.

Step 3 - Hydrolysis of the -CN group, to yield an alpha amino acid.

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8
Q

What is the Henderson-Hasselbalch equation? What is it used for?

A

pH = pKa + log( [Base] / [Acid] )

It is used to calculate the pH of buffer solutions.

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9
Q

Describe sphingolipids.

A

They are a class of membrane lipids. They have a polar head group anad two nonpolar tails, but they do not contain glycerol. Their backbone is formed by a molecule called sphingosine (an amino alcohol). They are found in neural cells. They help form the myelin sheath.

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10
Q

Which are more stable, imines or oximes? Why?

A

Oximes are more stable, because the oxygen has a lone pair of electrons, which increases stability via resonance.

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11
Q

What is the relationship between Ka and Kb?

A

For the Ka of an acid and the Kb of its conjugate base:

Ka x Kb = Kw

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12
Q

Define Arrhenius Acid

A

Any species that increases the [H+] in aqueous solution

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13
Q

Explain the process of extraction. What is the goal of extraction? What equipment do you need?

A

Extraction can be used to separate compounds based on their different solubilities in two different solvents. A separatory funnel is used.

Examples:

hexane can be separated from phenol by deprotonating the phenol.

hexane can be separated from propanamine by protonating the propanamine.

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14
Q

What is the formula for hydrogen sulfate (aka bisulfate)

A

HSO4-

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15
Q

Name this compound: SCN-

A

Thiocyanate

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16
Q

What is the mobile phase in paper chromatography?

A

Liquid.

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17
Q

Define what it means for an object to be chiral.

A

A chiral object is NOT superimposable on its mirror image.

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18
Q

Using the Pauling scale, how do you know if a bond is polar covalent, nonpolar covalent, or ionic?

A

If the difference in electronegativity between the two atoms is <~0.5 Pauling units, it is nonpolar.

If the difference in electronegativity between the two atoms is between ~0.5 and ~1.7 Pauling units, it is polar.

If the difference in electronegativity between the two atoms is >~1.7 Pauling units, it is ionic.

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19
Q

What is the formula for sulfite?

A

SO32-

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20
Q

Describe the general structure of an iminium ion.

A

It is basically a protonated imine. It has a (former) carbonyl carbon double-bonded to a nitrogen, which has a hydrogen and an R group. The N has a formal charge of +1.

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21
Q

Describe HPLC.

A

It is essentially the same as regular liquid column chromatography, but it can be used with very small quantities of sample, and the detector is much more sensitive and has higher resolving power.

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22
Q

In thin-layer chromatography, compounds are separated based on what property?

A

Polarity.

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23
Q

Describe the general structure of a cyanohydrin.

A

It is when a (former) aldehyde or ketone has 4 things bonded to its central carbon: a CN group, an OH group, and two R groups (1 of these would be H, in an aldehyde).

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24
Q

What is the mobile phase in size-exclusion chromatography?

A

Liquid.

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25
Q

What is the mobile phase in liquid column chromatography?

A

Liquid.

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26
Q

What is the stationary phase in thin-layer chromatography?

A

Solid (silica or alumina).

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27
Q

What is a pyranose?

A

It is a sugar that has a 6-membered ring in its structure.

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28
Q

Define Lewis Acid

A

An electron pair acceptor

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29
Q

What is the mobile phase in affinity chromatography?

A

Liquid.

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30
Q

Name this compound: HClO4

A

Perchloric acid

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31
Q

What is the formula for nitric acid?

A

HNO3

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32
Q

How does ion-exchange chromatography work? Which types of compounds elute first?

A

The stationary phase is composed of a cationic or anionic resin. Molecules that have the same charge as the resin will elute quickly. Molecules that have the opposite charge as the resin will elute slowly.

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33
Q

Explain the stereochemistry involved in oxime formation.

A

If the starting ketone or aldehyde is not symmetrical, the oxime will form both possible stereoisomers (E and Z versions of the molecule, with different arrangements around the C=N double bond).

This is theoretically possible with imines too, but imines are not as stable as oximes, so it is more difficult to isolate the imine stereoisomers.

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34
Q

Is hemiacetal formation catalyzed by acid, base, or both?

A

Both.

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35
Q

Name this compound:

C2O42-

A

Oxalate

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36
Q

Name the 2 main ways to synthesize alpha amino acids in the lab.

A
  1. Gabriel synthesis
  2. Strecker synthesis
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37
Q

What is the stationary phase in liquid column chromatography?

A

Solid (silica or alumina).

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38
Q

Define Bronsted-Lowry Acid

A

A proton donor

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39
Q

In ion-exchange chromatography, compounds are separated based on what property?

A

Ionic charge of the molecules.

40
Q

What is the formula for chromate?

A

CrO42-

41
Q

Explain the difference between the kinetic and thermodynamic enolate. How do you favor the formation of one over the other?

A

The kinetic enolate forms faster, but the thermodynamic enolate is more stable.

For example, think of 2-butanone. The kinetic enolate has lost a proton from the methyl group (this forms faster, because it is less sterically hindered, and because there are 3 methyl H’s vs 2 at the other alpha carbon). The thermodynamic enolate has lost a proton from the alpha carbon in the ethyl group (this is more stable, because the double bond is more substituted).

LDA (bulky) with low temp will form kinetic enolate. NaH with normal/high temp will form thermodynamic enolate.

42
Q

What is mutarotation?

A

Mutarotation occurs when there is an equilibrium between alpha and beta anomers. This happens because the ring can open and re-form in aqueous solution.

Example: if the alpha anomer of glucose is dissolved in water, some of it will slowly convert to the beta anomer. This causes the specific rotation to change, and approach its equilibrium value. If the experiment is repeated with the pure beta anomer, its specific rotation will approach the same equilibrium value.

43
Q

What is a holoenzyme?

A

A biochemically active compound formed by the combination of an enzyme with a coenzyme.

In other words, once the enzyme is combined with its coenzyme, it is considered “complete”.

44
Q

Is acetal formation catalyzed by acid, base, or both?

A

Acid only.

45
Q

What is a retro-aldol reaction?

A

A reaction in which a beta-hydroxy carbonyl compound decomposes into an aldehyde or ketone, plus another carbonyl compound.

46
Q

What is the formula for peroxide?

A

O22-

47
Q

What is the leaving group in an aldol condensation / dehydration? Why is it able to leave? What is the final product?

A

The leaving group is OH-

It is able to leave, because the final product is an alpha-beta unsaturated carbonyl compound (the hydroxide leaves in an exothermic step).

48
Q

Define chirality center.

A

A tetrahedral carbon with 4 different groups bonded to it.

49
Q

What is the stationary phase in ion-exchange chromatography?

A

Solid (cationic or anionic resin).

50
Q

What is the difference between reducing and non-reducing sugars?

A

A reducing sugar can acting as a reducing agent because it has a free aldehyde or ketone group. All monosaccharides are reducing sugars, along with some di-, oligo-, and polysaccharides.

Nonreducing disaccharides have acetal functional groups, which do not easily switch to the open-chain form.

Reducing disaccharides have hemiacetalfunctional groups, whichcan easily switch to the open-chain form.

Reducing disaccharides have only one of their two anomeric carbons involved in the glycosidic bond, meaning that they can convert to an open-chain form with an aldehyde group.

51
Q

In size-exclusion chromatography, compounds are separated based on what property?

A

Size of the molecules.

52
Q

Describe the general structure of a hydrazone.

A

It is an imine that has an NH2 group bonded to the “main” nitrogen atom (the one that forms a C=N double bond).

53
Q

What is the stationary phase in gas chromatography?

A

Liquid on a solid support.

54
Q

What is the mobile phase in ion-exchange chromatography?

A

Liquid.

55
Q

What is the stationary phase in size-exclusion chromatography?

A

Solid (microporous beads of silica).

56
Q

What is the formula for thiocyanate?

A

SCN–

57
Q

What is the formula for thiosulfate?

A

S2O32-

58
Q

What is the mobile phase in gas chromatography?

A

Inert gas.

59
Q

Describe the general structure of a carbinolamine.

A

It consists of a former aldehyde or ketone. The central carbon has two R groups (one of these is an H if you started with an aldehyde), an OH group, and an NHR group.

It is an intermediate in the formation of an imine.

60
Q

What is the mneumonic for remembering how to go from a Fisher to a Haworth projection?

A

“Downright uplefting”

The left side of the Fisher projection points up in the Haworth.

The right side of the Fisher projection points down in the Haworth.

61
Q

What is Kw?

A

The autoionization constant, aka the ion product constant. Kw = 10-14 at 25°C.

62
Q

Define Arrhenius Base

A

Any species that increases the [OH-] in aqueous solution

63
Q

What is the difference between normal-phase and reverse-phase chromatography?

A

In normal-phase, the stationary phase is polar and the solvent is nonpolar.

In reverse-phase, the opposite is true.

64
Q

Name this compound: O22-

A

Peroxide

65
Q

Describe the general structure of an oxime.

A

It is an imine in which the nitrogen atom has an OH bonded to it.

66
Q

Is 1,1,1-Trichloroacetone more or less likely to form a hydrate than acetone? Why?

A

1,1,1-Trichloroacetone is more likely to form a hydrate, because the 3 chlorine atoms withdraw electron density from the carbonyl carbon, making it even more electrophilic.

67
Q

Explain the Gabriel synthesis. What are the reagents and steps involved? What is the final product?

A

Start with N-phthalimidomalonic ester.

Step 1 - Add base

Step 2 - Add R-X to alkylate the alpha carbon (replace the H with X)

Step 3 - Add acid (to hydrolyze the phthalimodo group and the esters)

Step 4 - Add heat to decarboxylate, thus forming the final product (racemic alpha amino acid)

68
Q

What are epimers?

A

They are a pair of diastereomers that only differ at one chiral center.

69
Q

Name this compound: S2O32-

A

Thiosulfate

70
Q

What is a glycosidic bond?

A

A glycosidic bond is a type of covalent bond that joins a carbohydrate molecule to another group, which may or may not be another carbohydrate.

A glycosidic bond is formed between the hemiacetal group of a saccharide and the hydroxyl group of some compound such as an alcohol.

71
Q

Name this compound: HNO3

A

Nitric acid

72
Q

What is the stationary phase in affinity chromatography?

A

Solid (Beads with immobilized “special” molecules, such as enzymes or antibodies).

73
Q

Is keto-enol tautomerization catalyzed by acid, base, or both?

A

Both.

74
Q

What is the name of the device used on the “top” during a titration (the device that measures how much titrant you are adding)?

A

Burette.

75
Q

In gas chromatography, compounds are separated based on what property?

A

Mainly the boiling points of the compounds, but also MW and polarity.

76
Q

What is the structure of hydrazine?

A

H2N-NH2

77
Q

Name this compound: H2N-NH2

A

Hydrazine.

78
Q

Define Lewis Base

A

An electron pair donor

79
Q

What is the term for a molecule that can act as either an acid or a base?

A

Amphoteric

80
Q

What is the stationary phase in paper chromatography?

A

Solid (cellulose).

81
Q

Name this compound: HSO4-

A

Hydrogen sulfate (aka bisulfate)

82
Q

In liquid column chromatography, compounds are separated based on what property?

A

Polarity.

83
Q

Define Bronsted-Lowry Base

A

A proton acceptor

84
Q

What is a furanose?

A

It is a sugar that has a 5-membered ring in its structure.

85
Q

What are anomers?

A

Anomers are a special kind of epimer pair. Anomers are epimers at the hemiacetal/acetal carbon in a cyclic saccharide, an atom called the anomeric carbon (the carbon derived from the carbonyl group in the straight-chain sugar).

86
Q

How does gas chromatography work? Which types of compounds elute first?

A

The sample is heated, and inert gas is passed over it. The sample will vaporize and be swept into the column with the inert gas. The column consists of a tube coated with liquid. High boiling point, high MW, and high affinity between the sample and the stationary phase will all tend to increase the time it takes for the sample to elute.

87
Q

What is Tollens’ reagent? What does it do? What types of compounds does it react with? Why does it react with some things but not others?

A

Tollens reagent: Ag+, OH-, and NH3. When they are combined, they will form [Ag(NH3)2]+.

It reacts with aldehydes and alpha-hydroxy ketones.

This reaction will oxidize an aldehyde to a carboxylate anion, while depositing metallic silver.

Tollens reagent is a mild oxidizing agent, so it is not strong enough to oxidize most ketones. Aldehydes are more reactive, so easier to oxidize.

88
Q

Name this compound: Cr2O72-

A

Dichromate

89
Q

How does size-exclusion chromatography work? Which types of compounds elute first?

A

The stationary phase is composed of microporous beads. Small compounds get trapped in the beads and elute slowly. Large compounds do not get trapped in the beads, and elute quickly.

90
Q

Will glucose react with Tollens reagent? Why or why not?

A

Yes, Tollens reagent will react with the open-chain form of glucose. Although the cyclic forms (alpha and beta anomers) predominate, they are in equilibrium with the open-chain form. When the open-chain form reacts with Tollens reagent, it is removed from solution, thus pulling more cyclic forms back to the open-chain form (Le Chatelier’s principle).

91
Q

What is the formula for dichromate?

A

Cr2O72-

92
Q

In affinity chromatography, compounds are separated based on what property?

A

Binding affinity between the compound and the “special” molecule (enzyme or antibody) that is immobilized in the column.

93
Q

In paper chromatography, compounds are separated based on what property?

A

Polarity.

94
Q

Define amphoteric

A

Capable of acting as an acid or a base

95
Q

What is the formula for oxalate?

A

C2O42-

AA JW Science Review (6 decks)

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