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Organic Chemistry Flashcards

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1
Q

What is a retro-aldol reaction?

A
  • The reverse of a aldol condensation
  • To push the reaction in a retro-aldol direction, aqueous base is added and heat is applied
  • Retro-aldol reaction is useful for breaking bonds between the α and β-carbons of a carbonyl
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2
Q

When would we use distillation? What is distillation?

A
  • Use the product is a liquid that is soluble in the solvent
  • Distillation takes advantage in the differences in bioling point to separate two liquids by evaporation and condensation
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3
Q

What compounds can oxidize secondary alcohols to ketones?

A

PCC, or any strong oxidant (KMnO4, Na2Cr2O7, etc.)

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4
Q

What are the major factors that determine nucleophilicity? How do they change nucleophilicity?

A
  • Charge: nucleophilicity increases with increasing electron density (more negative charge)
  • Electronegativity: nucleophilicity decreases as electronegativity incrases becasue these atoms are less liekly to share electron density
  • Steric hindrance: bulkier molecules are less nucleophilic
  • Solvent: protic solvents can inhibit nucleophilicity by nortonating the nucleophile or hydrogen bonding
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5
Q

What is saponification?

A
  • When long-chain carboxylic acids react with sodium or potassium hydroxyide, a salt is formed; this is saponification
  • This produces a soap, which can solvate nonpolar organic compounds in aqueous solutions because they contain both a nonpolar tail and a polar carboxylate head
  • When places in aqueous solution, they create micelles
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6
Q

Where would you find alkynes groups on an NMR?

A

2 to 3 ppm

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7
Q

Describe the basics of the Strecker synthesis.

A
  • Starts with an aldehyde, ammonium chloride (NH4Cl), and potassium cyanide (KCN)
  • Ammonia attacks the carbonyl carbon, generating an imine
  • The imine is attacked by the cyanide, generating an aminonitrile
  • The aminonitrile is hydrolyzed by two equivalents of water, generating an amino acid
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8
Q

What is an aldol condensation? What is the mechanism?

A
  • An aldehyde or ketone acts both as an electrophile (in its keto form) and a nucleophile (in its enol or enolate form), reacting to form a carbon-carbon bond

Step 1, Form the aldol: an enolate ion is form, which then attacks the carbonyl carbon, forming an aldol

Step 2, Dehydration of the aldol: the -OH is removed as water, forming a double bond

  • With a strong base and high temperatures, dehydration occurs by an E1 or E2 mechanism, forming a double bond, producing an α, β unsaturated carbonyl
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9
Q

What products can you use to take a carboxylic acid and create a primary alcohol?

A

LiAl4

  • NaBH4 is not strong enough to reduce carboxylic acids
  • Remember: can only be a primary alcohol, because it’s bonded to only one R group
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10
Q

What is a geminal diol?

A

diols with hydroxyl groups on the same carbon

  • Not commonly seen because they spontaneously dehydrate (lose a water molecule) to produce carbonyl compounds with functional group C=O
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11
Q

How does fractional distillation work?

A
  • A fractionation column, which is a column in which the surface area is increaed by the inclusion of inert objects like glass beads or steel wool, connects the distillation flask to the condenser
  • As the vapor rises up the column, it condenses on these surfaces and refluxes black down, until rising heat causes it to evaporate again, only to condense again higher in the column
  • Each time the condensate evaportes, the vapor consists of a higher proportion of the compound with the lower boiling point
  • Byt he time the top of the column is reached, only the desired product drips down to the receiving flask
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12
Q

What is column chromatography, generally?

A
  • Uses an entire column filled with silica or aluminum beads as an adsorbent, allowing for much greater separation
  • Uses gravity to move the solvent and compounds down the column
  • A sample is added to the top of the column, and a solvent is poured over it; the more similar the sample is to the mobile phase, the fater it elutes; the more stimilar it is to the stationary phase, the more slowly it will elute (if at all)

Types: ion-exchange chromatography, size-exclusion chromatography, affinity chromatography

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13
Q

What does the suffix -dioic acid indicate?

A
  • Molecules which have a carboxylic acid at each end
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14
Q

How can you form an aldehyde or ketone?

A
  • By using PCC on a primary or secondary alcohol
  • Any stronger reagent, and the carbonyl will be further oxidized to a carboxylic acid
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15
Q

What are phenols?

A
  • When hydroxyl groups are attached to aromatic rings
  • Hydroxyl hydrogens are particularly acidic due to resonance within the phenol ring
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16
Q

What compounds oxidize primary alcohols to carboxylic acids?

A
  • Any strong oxidizing agent
  • EXCEPT for PCC
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17
Q

Why is the dipole of the carbonyl stronger than the dipole of an alcohol?

A
  • Because the double bonded oxygen is more electron-withdrawing
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18
Q

Describe, generally, how chromatography works.

A
  • Begins by palcing a sample on to a solid medium called the stationary phase
  • We then run the mobile phase, ususally a liquid or gas through the stationary phase
  • This will displace the sample and carry it through the stationary phase
  • Depending on the characteristics of the subtances in the sample and the polarity of the mobile phase, it will adhere to the stationary phase with differing strengths, causing the different substances to migrate at different speeds
  • This is called partitioning
  • Different compounds will have different partitioning coefficients and will elute at different rates
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19
Q

What are some reductions that LiAlH4 can produce?

A
  • Aldehydes, ketones and carboxylic acids can be reduced to alcohols by LiAlH4
  • Amides can be reduced to amines by LiAlH4
  • Esters can be reduced to a pair of alcohols by LiAlH4
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20
Q

When would we use fractional distillation?

A
  • To separate two liquids with similar boiling points (less than 25°C) apart
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21
Q

In an extraction, what are the two layers that are formed?

A
  • Aqueous phase : polar or water layer
  • Organic phase: nonplar layer
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22
Q

What types of compounds are likely to decarboxylate when heated?

A
  • A carboxylic acid with a carbonyl on the β-carbon
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23
Q

Describe how thin-layer/paper chromatography works.

A
  • Spotting: we apply a small, well-defined spot of the sample directly onto the silica (thin layer) or paper (paper) plate
  • Development: place the adsorbent upright in a dveloping chamber, usually a bearker or wide-mouthed jar; at the bottom of this jar is the eluent
  • The solvent will creep up the plate by capillary action, carrying the various compounds in the sample it at varying rates
  • When the solvent front nears the top of the plate, the plate is removed from teh chamber and allowed to dry

Note: silica gel is polar and hyrdophilic and the mobile phase is usually an organic solvent of weak to moderate polarity; thus the more nonpolar the sample is, the further up the plate it will move

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24
Q

Describe the basics of the Gabriel synthesis.

A
  • Phtalimide attacks diethy bromomalonate, generating phthalimidomalonic ester
  • The phtalimidomalonic ester attacks an alky l halide, addaing an alkyl group to the ester
  • The product is hydrolyzed, creating a phtalmic acid (with two carboxyl groups) and converting the esters into carboxylic acids
  • One carboxylic acid of the resulting 1,3 dicarbonyl is removed by decarboylcation
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25
Q

Why does the Strecker synthesis provide maximum 50% of yield?

A
  • The starting material for the Strecker synthesis is a planar carbonyl-containing compound; therefore, the product of this pathway is a racemic mixture
  • The incoming nucleophiles are equally able to attack from either side of this carbonyl, thus, both L- and D- amino acids can be generated through this process
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26
Q

What is an α carbon?

A
  • refers to the first carbon atom that attaches to a functional group, such as a carbonyl
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27
Q

What type of mixture will be optically active?

A
  • Molecules with a chiral center
  • At the molecular level, one enantiomer will rotate plane-polarized light to the same magnitude but in the opposite direction of its mirror image
  • If it rotates clockwise, the molecule is dextroratory (d-) or +
  • If it rotates counter- clockwise, the molecule is levortatory (l-) or -
  • When both (+) and (-) enantiomers are present in equal concentrations, they form a racemic mixture; these rotations cancel each other out, and no optical activity is produced

Note: if an enantiomer has a plane of symmetry (a meso-compound), it will display no optical activity

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28
Q

What is transesterification?

A

The process of exchanging the organic group R″ of an ester with the organic group R′ of an alcohol. These reactions are often catalyzed by the addition of an acid or base catalyst.

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29
Q

What does ortho-, meta- and para- indicate?

A
  • The relative position of two groups on an aromatic compound

Ortho- (or o-): two groups on adjacent carbons

Meta- (or m-): two groups separated by a carbon

Para- (p-) two groups on opposite sides of the ring

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30
Q

In the presence of water, aldehydes and ketones form what compound?

A
  • Geminal diols
  • The nuclepphilic oxygen in water attacks the carbonyl carbon
  • This hydration reaction normally proeeds slowly but we can increase the rate by adding a small amount of catalytic acid or base
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31
Q

In infrared speoctrsocopy, where would you find a C=O?

A
  • 1750cm-1 , sharp
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32
Q

What is a vicinal diols?

A
  • diols with hydroxyl groups on adjacent carbons
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33
Q

What is the mechanism by which anhydrides are formed?

A
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34
Q

What is an enantiomer?

What is a diasteromers?

A
  • Enantiomers: have the same connectivity, but opposite configurations at every chiral center in the molecule; non-superimposible mirror images

Diastereomers: non-mirror image configurationsal isomers; occur when a molecule has two or more stereogenic centers and differs at some, but not all, these centers

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35
Q

In infrared spectroscopy, where would you find a C-H ?

A

2800-3000 cm-1

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36
Q

In infrared spectroscopy, where would you find a N-H ?

A

3300 cm-1, sharp

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37
Q

Where would you find aldehyde groups on an NMR?

A

9 to 10 ppm

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38
Q

What molecules are formed by a condensation reaction with carboxylic acid?

A
  • Esters
  • Amides
  • Anhydrides
  • In a condensation reaction, two molecules are cmbined to form one, with the loss of a small molecule (usually water)
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39
Q

How is a carboxylic acid synthesized?

A
  • Via oxidation of aldehydes and of primary alcohols
  • Use things like KMnO4
  • Note: Ketones and secondary and tertiary alcohols cannot be oxidized to carboxylic acids because they have at least two other bodns to other carbons
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40
Q

What is an imine?

A

containing a carbon–nitrogen double bond.

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41
Q

What is an amide?

A
  • A carboxylic acid derivative in which the hydroxyl group is replaced by a nitrogen group
  • This nitrogen can be bound to zero, one or two alkyl groups
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42
Q

What are lactams?

A

Amides that are cyclic (replace the -oic acid suffix with -lactam)

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43
Q

What is enamination? What are the compounds involved? Which is thermodynamically favored?

A

Imine, a compound that contains an C=N bond, can undergo tautomerization (movement of a hydrogen and a double bond) in order to produce an enamine

The imine form is thermodynamically favored over the enamine form

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44
Q

What are the physical properties of a molecule?

A
  • Characteristics of processes that don’t change the composiion of matter
  • Include: melting point, boiling point, solubility, odor, color and density
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45
Q

In an SN2 reaction, what is the sterochemistry of the product?

A
  • SN2 reactions are accompanied by a inversion in relative configuration; the position of the substituents around the substrate will be inverted
  • If the nucleophile and leaving group have the same priority in their respective molecules, this inversion will also correspond to a change in absolute configuration
46
Q

What is an extraction?

A
  • A process by which we separate a compound from a mixture
  • As polar substances will dissolve best in polar solvents and non-polar substances will dissolve best in non-polar substances, we can utilize two immiscible solvents to pull a compound into a particular solvent
  • Once we have the layer of interest, we can evaporate away the solvent, leaving us with the product alone (use a rotary evaporator)
47
Q

With the addition of one equivalent of alcohol, a ketone or aldehyde gets made into a hemiketal or hemiacetal. Describe this reaction.

A
  • The oxygen in the alcohol functions as a nucleophile, attacking the carbonyl carbon and generating a hemiacteal
48
Q

What is the resulting compound after treating phenols with oxidizing agents?

A

Quinones

  • Quinones are resonance stabilized electrophiles
  • Quinones are named by indicating the position of the carbonyls and adding quinone to the name of the parent phenol
49
Q

What is affinity chromatography?

A
  • A type of column chromatography
  • A protein of interest is bound by creating a column with high affinity for that protein; this can be accomplished by coating beats with a receptor that binds the protein or a specific antibody to the protein
  • Once the protein is retained in the column, it can be eluted by washing the column with a free receptor (or target or antibody), which will compete with the bead-bound receptor and ultimately free the protein from the column
50
Q

What is an anhydride?

A
  • A carboxylic acid derviatve, in which one molecule of water is removed and a bond is formed between two caroxylic acid molecules
51
Q

Aldehydes can be oxidized into what compounds?

A
  • Into carboxylic acids
  • Can occur by any oxidizing agent, sch as KMnO4, CrO3, Ag2O, H2O2
  • Note: PCC will stop at carbonyls when oxidizing alcohols, so PCC will not turn a carbonyl into a carboxylic acid
52
Q

Where would you find alkenes groups on an NMR?

A

4.6 to 6 ppm

53
Q

What is the function of filtration? How would one perform a filtration?

A
  • Isolates a solid from a liquid
  • Poour a liquid-solid mixture onto a paper filter that allows only the solvent to pass through
  • At the end of filtration, one is left with the solid, called the residue, and flask full of liquid, called the filtrate
54
Q

Why are dicarboxylic acids more acidic than their monocarboxylic acid counterparts?

A
  • Carboxylic acids are electron-withdrawing due to the electronegative oxygen atoms they contain
  • Thus, in a dicarboxylic acid, each -COOH group influences the other -COOH group
  • The net result is that dicarboxylic acids are more acidic than their analogous monocarboxylic acids
55
Q

What type of products would you use simple distillation for?

A
  • Should only be used to separate liquids that boil below 150°C and have at least a 25°C difference in boiling points
  • This prevents the temperature from becoming so high that the compounds degrade and provide a large enough difference in boiling points that the second compound won’t accidentally boil off into the distillate
56
Q

How is imine formed?

A

Ammonia is added to a carbonyl containing group, resulting in the elimination of water and generating a imine

57
Q

What is an amine?

A

contain a basic nitrogen atom with a lone pair

58
Q

Of the carboxylic acid derivatives, list the reactivity, from most to least reactive

A
  • Ahydrides: with their resonance stabilization and three electron-withdrawing groups are most electrophlic
  • Esters (tied with carboxylic acids)
  • Amides
59
Q

What is a ketone?

A
  • A carbonyl group somewhere in the middle of the carbon chain
  • Becuase this is the case, we will always have to assign a number to the carbonyl carbon
60
Q

Since the hydrogen on the hydroxyl group of a carboxylic acid is very acidic, it can leave, leaving a carboxylate group. How does electron-withdrawing or electron-donating groups effect the stability of this carboxylate?

A
  • Electron-withdrawing groups, like -NO2 or halides increase the acidicity
  • Electron-donating groups will destablize the negative charge and decrease acidity.
61
Q

How are amides hydrolyzed? What is the product?

A
  • Can be hydrolyzed under acidic conditions via nucleophlic substitution
  • Acidic conditions allow the carbonyl oxygen to become protonated, making the molecule more susceptible to nucleophilic attack by a water molecule
  • Product is a carboxylic acid and an ammonia
  • Note: this can also occur under highly basic conditions, where the attacking nucleophile is the hydroxide ion
62
Q

Where would you find aromatic groups on an NMR?

A

6 to 8.5 ppm

63
Q

When would one use gravity filtration? Vaccuum filtration?

A
  • Gravity filtration, in which the solvent’s own weigh pulls it through the filter, is more commonly used when the product of interest is in the filtrate
  • Vacuum filtration, in which the solvent is forced through the filter bya a vacuum, is more often used when the solid is the desired product
64
Q

In infrared spectroscopy, where would you find a O-H ?

A

3300cm-1 , broad

65
Q

In an SN1 reaction, what is the sterochemistry of the product?

A
  • Because SN1 reactions pass trhough a palanr intermediate before the nucleophile attacks, the product will usually be a racemic mixture
  • The incoming nucleophile can attack the carbocation from either side, resulting in varied stereochemistry
66
Q

Where would you find carboxylic acids on an NMR?

A

10.5 to 12 ppm

67
Q

What occurs in cyanohydrin formation?

A
  • HCN has both triple bonds and an electronegative atom, rendering it an extremely acidic compound
  • After the hydrogen disocciates, the nucleophilic cyanide anion can attack the carbonyl atom
  • Then, the oxygen gets reprotonated, creating a cyanohydrin
68
Q

If an aldehyde is attached to a ring, what suffix is used?

A
  • carbaldehyde

Example: cyclopentanecarbaldehyde

69
Q

What are lactones?

A
  • Esters that are cyclic
70
Q

Why do aldehydes and ketones act as electrophiles?

Which is more reactive: aldehydes or ketones? Why?

A
  • Becuase the double bonded oxygen pulls electrons from the carbon, creating a partial positive charge on the carbon
  • Aldehydes are more reactive because they have less steric hindrance than ketones
71
Q

If comparing an alcohol and a aldehyde/ketone with regard to boiling point, which one has a larger boiling point?

A
  • While the double bonded oxygen in an aldehyde or ketone makes for a larger dipole moment, alcohols have higher boiling points, because they can engage in hydrogen bonding, whereas aldehydes and ketones cannot
72
Q

Given that a ketone has two different alkyl groups, each of which may have α hydorgens, two forms of the enolate can form. What are these?

A
  • Kinteic enolate: formed rapidly but is less table; has a double bond to the less substituted α-carbon
  • Thermodynamic enolate: formed more slowly, but is more stable and features a double bond being formed with the more substituted α-carbon
73
Q

What are the chemical properties of a molecule?

A
  • Has to do with the reacitivity of a molecule and results in changes in chemical composition; the chemical properties of a compound are generally dicated by the functional groups in the molecule
74
Q

How would you name an amide?

A
  • Replace the -oic acid suffix with amide
  • Alkyl subsitutents on the nitorgen atom are listed as prefixes, and their location is specified with the letter N
75
Q

What is a Lewis acid?

A
  • An electron acceptor in the formation of a covalent bond
  • Have vacant p-orbitals into which they can accept a electron pair, or are positively polarized atoms
76
Q

What is a conformational isomer?

A
  • An isomer that is created by rotation around a single bond
77
Q

What compounds can “cleave” an anhydride? What is the result of this?

A
  • Addition of ammonia or amine results in an amide and carboxylic acid
  • Addition of an alcohol results in an ester and a carboxylic acid
  • Addition of water results in two carboxylic acids
78
Q

Where would you find alkyl groups on an NMR?

A

0 to 3 ppm

79
Q

When would we use vacuum distillation?

A
  • Whenever we want to distill a liquid with a boiling point over 150°C
  • By using a vacuum, we lower the pressure, thereby decreasing the temprature that liquid must reach in order to boil
  • This allows us to distill compounds with higher boiling points at lower temperatures so that we do not have to worry about degrading the product
80
Q

What is reverse-phase chromatography?

A
  • The same type of chromatography as thin-layered chromatography, except the phases are opposite, i.e. the stationary phase is nonpolar, so polar molecules move up the phase more quickly
81
Q

What can you use to turn aldehydes and ketones into alcohols?

A
  • Hydride reagents, such as LiAl4 and NaBH4
82
Q

Due to the acidity of the α-hydrogen, aldehydes and ketones exist in solution as a mixture of two isomers. What are these isomers?

A
  • Keto and enol (constitutional isomers)
  • Differ in the placement of a proton and double bond, are called tautomers
  • Equilibrium lies far to the keto side
83
Q

What is the process of recrystallization? What do we use it for?

A
  • A method for further purifying crystals in solution
  • We dissolve our product in a minimum amount of hot solvent and let it recrystallize as it cools
  • The solvent chosen for this process should be one in which the product is souble only at high temperatures; thus, when the solution colls, onlythe desired product will recrystallize out of solution, excluding the impurities
84
Q

Why are the α-hydrogens near a carbonyl more acidic than in a regular C-H bond?

A
  • Due to the resonance stabilization of the enol form
  • These can be easily deprotonated with a strong base, forming an enolate, which is a strong nucleophile
  • The alpha-protons of carbonyls are somewhat acidic: the pKa of acetone, for example, is approximately 19. In the formation of an enol, a base abstracts an a-proton from a carbonyl compound, and that same proton (or a proton on a nearby acid group) is transferred to the carbonyl oxygen. The result is a new functional group that combines both alkene and alcohol characteristics - hence the term enol. The deprotonated form of an enol is an enolate
85
Q

What is a nucleophile?

A
  • “nucleus-loving” species with either a lone pair or π bond that can be used to form new bonds to electrophiles
  • Good nucleophiles tend to be good bases
86
Q

How can we use alcohols as protecting groups for aldehydes and ketones?

A
  • Aldehydes and ketones can be reacted with two equivalents of alcohol or a diol forming acetals (primary carbons with two -OR groups and a hydrogen atom) or ketals (secondary carbons with two -OR groups)
  • Carbonyls can react with LiAlH4, for eample, but acetals and ketals do not
  • The acetal or ketal can be reverted back to a cabonyl with an aqueous acid in a step called deprotection
87
Q

What is a β-lactam? What is a δ-lactam?

A

β-lactam: contain a bond between the β-carbon and the nitrogen

δ-lactam: contain a bond between the δ-carbon and the nitrogen

88
Q

What occurs when you add alcohol to an aldehyde or ketone? What type of reaction is this?

A
  • When one equivalent of alchol is added to aldehydes or ketones, the product is a hemiacteal or hemiketal
  • When an additional equivalent of alcohol is added, the reaction forms acetals or ketals
89
Q

What is Jones oxidation?

A
  • An organic reaction for the oxidation of primary and secondary alcohols to carboxylic acids and ketones, respectively
  • Jones reagent consists of chromium trioxide and sulfuric acid dissolved in a mixture of acetone and water.
  • The oxidation is very rapid, quite exothermic, and the yields are typically high
90
Q

What is the relative acidity of the protons on a dicarboxylic acid?

A
  • The first proton is very acidic, given that the other -COOH group is electron-withdrawing
  • However, the second one is less acidic after the first one is removed, because removal of two on the same molecule would give rise to two negative charges and thus repulsion
  • Thus, comparing a dicarboxylic acid to a monocarboxylic acid, the first proton on the dicarboxylic acid is most acidic, then the proton on the monocarboxylic acid is next, and then the second proton on the dicarboxylic acid is least acidic
91
Q

Why, when in basic solution, will α-hydrogens readily deprotonate? Is this stable?

A
  • The carbonyl group pulls electron density away from the C-H bonds, weakening them
  • Once removed, the extra electrons that remain can resonate between the α-carbon, the carbonyl carbon and the carbonyl oxygen, increasing the stability of the enolate intermediate
  • The oxygen carbonyl stabilizes the newly formed carbanion
92
Q

What are structural isomers?

A
  • Also called constitutional isomers
  • Share their molecular formula and thus molecular weights
93
Q

What are the three types of ring strain that can affect the cyclic conformation of a molecule?

A

Angle strain: results when bond angles deviate from their ideal values by being stretched or compressed

Torsional strain: results when cyclic molecules must assume conformations that have eclipsed or gauche interactions

Non-bonded (van der Waals) repulsion: results when nonadjacent atoms or groups compete for the same space

94
Q

How do boiling points of alcohol relate to boiling points of their associated hydrocarbons?

What occurs with the addition of further hydroxyl groups?

A
  • Since alcohols are capable of intermolecular hydrogen bonding, they have signficiantly higher melting and boiling points than those of analogous hydrocarbons
  • When additional hydroxyl groups are added, boiling point increases, since more hydrogen bonding can occur
95
Q

What is size-exclusion chromatography?

A
  • A type of column chromatography
  • the beads in the column contain pores of varying sizes
  • these tiny pores allow small compounds to enter the beads, thus slowing them down; large compounds cannot fit into the beads, so they move around them and travel through the column faster
  • Can vary the size of the pores so that molecules with different molecular weights may be fractionated
  • Used in protein purification
96
Q

With regard to thin-layer chromatography, what is the retardation factor (Rf)?

A

Rf = distance spot moved/ distant solvent front moved

  • Rf values can be used to identify unknown compounds
97
Q

What is esterification?

A
  • A condensation reaction, with water as a side product
  • Esters aremade by reacting a carboxylic avid with alcohol under acidic conditions

Process:

  • In an acidic solution, the carbonyl can be protnated, which enhances the polarity of the bond, thereby placing additional positive charge on the carbonyl carbon and increasing its suceptibility to attack
  • Lone pair on an alcohol will attack the carbonyl carbon
  • The hydroxyl group on the carboxylic acid gets protonated and gets kicked off
  • This leaves a protonated (on the caronbyl) ester
  • The H+ leaves

-

98
Q

What is an enamine?

A

An unsaturated compound derived by the condensation of an aldehyde or ketone with a secondary amine

  • If one of the nitrogen substituents is a hydrogen atom, H, it is the tautomeric form of an imine
99
Q

Primary alcohols can be oxidized to aldehydes via what molecule?

A

Oxidation of a primary alcohol to an aldehyde is via PCC (pyridinium chlorochromate)

100
Q

What is Fischer esterification?

A

A special type of esterification by refluxing a carboxylic acid and an alcohol in the presence of an acid catalyst

Reaction Mechanism

  1. Proton transfer from acid catalyst to carbonyl oxygen increases electrophilicity of carbonyl carbon.
  2. The carbonyl carbon is then attacked by the nucleophilic oxygen atom of the alcohol
  3. Proton transfer from the oxonium ion to a second molecule of the alcohol gives an activated complex
  4. Protonation of one of the hydroxyl groups of the activated complex gives a new oxonium ion.
  5. Loss of water from this oxonium ion and subsequent deprotonation gives the ester.
101
Q

What does a pKa tell us about an acid or a base?

A

pKa= -log (Ka)

  • Acidic molecules will have a smaller (or even negative) pKa ; acids with a pKa below -2 are considered strong acids, which will almost always dissociate completely in aqueous solution
  • More basic molecules will have a larger pKa
102
Q

What is the reaction which converts carboxylic acids into amides?

A
  • The incoming nucleophile must be ammonia (NH3) or an amine
103
Q

What is ion-exchange chromatography?

A
  • A type of column chromatography
  • The beads in the column are coated with charged substances so that they attract or bind compounds that have an opposite charge
  • After all compounds have moved through the column, a salt gradient is used to elute the charged molecules that have stuck to the column

Example: a positively charged compound will attract and hold a negatively charged backbone of DNA or protein as it passes through the column, either increasing its retention time or retaining it completely

104
Q

What are electrophiles?

A
  • Electron loving species with a positive charge or positively polarizaed atoms that accepts an electron pair when forming new bonds
105
Q

What is nucleophilic acyl substition?

A
  • The nucleophilic molecule replaces the leaving group of an acyl derivative
  • Acyls encompass all moelcules with a carboxylic derived carbonyl, including carboxylic acids, amides, esters, anhydrides and otehrs
  • These reactions are favored by a good leaving group (weak bases are good leaving groups; weak bases are the conjugates of strong acids)
106
Q

What is an aldehyde?

A
  • Have a carbonyl group found at the en d of the carbon chain
  • Because this is a terminal functional group that takes prescedence, it is usually attached to carbon number 1
107
Q

Why would CH3OH have a more acidic proton than CH2H5OH?

A
  • The presence of more alkyl groups in a non-aromatic alcohols produces less acidic molecules
  • Because alkyl groups donate electron density, they destabilize the negative charge
108
Q

What is an ester?

A
  • The hydroxy group of a carboxylic acid is replaced with an alkoxy (-OR, where R is a hydrocarbon chain) group
  • A carboxylic acid derivative
109
Q

With the addition of one equivalent of alcohol, a hemiacetal or hemiketal gets made into a ketal or acetal. Describe this reaction.

A
  • Proceeds via SN1
  • Catalyzed by an anhydrouss acid
  • The hydroxyl group of the hemiacetal or hemiketal is protonated under acidic conditions and water is lost
  • A carbocation is thus formed and another equivalent of a,cohol attacks the carbocation, resulting in the formation of an acetal or ketal
110
Q

What is the purpose of making a hydroxyl group into a mesylate or tosylate?

A
  • Hydroxyl groups are faily poor leaving groups for nucleophilic substitution; however, they can be reacted to form much better leaving groups called mesylates and tosylates
  • Mesyl and tosyl groups can also serve as protecting groups when we do not want the -OH to react; these groups are protective in that they will not react with many of the other reagents that would attack alcohols, especially oxidizing agents
111
Q

What are they ways in which a straight chain conformation can appear in a Newman’s projection?

A
  • Anti-staggered: largest groups as 180° apart
  • most favorable
  • Gauche: largest groups are 60° apart
  • Eclipsed: largest groups are 120° apart
  • Totally eclipsed: largest groups are 0° apart
  • least favorable

MCAT (8 decks)

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