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MCAT: Biological Sciences > Organic Chemistry: General Principles > Flashcards

Organic Chemistry: General Principles Flashcards

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MCAT flashcards
0
Q

How do you name the chemicals?

A
  1. Find the longest chain containing the most important functional group
  2. Name the substituents
  3. Number the chain so that the lowest set of numbers are for the most important non-backbone groups (place the least important substituent away and number around to get R or S in enantiomers) (m, o, or p for aromatic rings) (cis, trans, Z, or E for alkenes)
  4. Alphabetized substituents
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1
Q

What shape does Carbon have and how does the shape change as the s character increases?

A

Carbon can accept four more electrons that could be sp3 (109.5°), sp2 (120°), or sp1 (180°) hybridized. The bond becomes shorter and more stable as the a character increases.

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2
Q

Alkane General Formula

A

CnH2n+2

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3
Q

Greek Prefixes

A 
Meth-
Eth-
Prop-
But-
Pent-
Hex-
Hept-
Oct-
Non-
Dec-
Undec-
Dodec-
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4
Q

Alkene (olefin) General Formula

A

CnH2n

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5
Q

What are vinyl- derivatives?

A

Mono-substituted ethylenes

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6
Q

What are allyl derivatives?

A

C-3 substituted propylenes

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7
Q

Isomers

A

Compounds withy the same formula, but different structures

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8
Q

What types of isomers have different connectivities?

A

Constitutional (Structural) Isomers

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9
Q

What types if isomers have the same connectivity but different spatial arrangement?

A

Stereoisomers

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10
Q

What are geometric isomers?

A

Diastereomers that involve different arrangements around a double bond. These could have different physical properties, but similar chemical reactivity.
Cis (Z) v. Trans (E)

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11
Q

Chirality

A

Handedness, describing how some mirror reflections are not superimposable. Carbon atoms must have for different substituents to be chiral.

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12
Q

Enantiomers

A

Stereoisomers with one chiral center that cannot be superimposed with its mirror image. These compounds have identical physical an chemical properties, except for optical activity.

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13
Q

Diastereomers

A

Stereoisomers with more than one chiral center and 2^n stereoisomers. These may have different physical properties.

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14
Q

Racemic Mixture

A

Equimolar mixture of enantiomers that displays no optical activity.

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15
Q

Meso Compound

A

Diasteromer with a plane of symmetry

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16
Q

Optical Activity

A

The ability to rotate plane-polarized light (+ or -)
The amount of rotation depends on the number of molecules that a light wave encounters ([optically active compound] and the length of the tube).
Specific Rotation = α = observed rotation/ (concentration (g/mL) X length (dm)

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17
Q

Conformational Isomers

A

Compounds that differ by rotation around single bonds.
Staggered —> gauche —> eclipsed
Lower energy —> higher energy
Low temperatures slow conformational interconversion.

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18
Q

What factors comprise ring strain?

A

Angle strain, torsional strain, and nonbonded strain

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19
Q

What are nucleophiles?

A

Electron-heavy molecules that attack positively polarized atoms. In protic solvents, larger atoms are the better nucleophiles. More basic atoms are better nucleophiles in aprotic solvents, because the nucleophiles are not solvated.

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20
Q

What make good leaving groups?

A

Weak bases make good leaving groups because they can accept an electron and dislocate to form a stable species.

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21
Q

What stabilizes carbocations?

A

Electron pair donating polar solvents, charge delocalization, and substitutions stabilize carbocations.

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22
Q

Describe the kinetics of SN1 reactions.

A

The rate limiting step is carbocations formation, therefore, the reaction is first order. Highly substituted allyl halides, polar solvents, and weak base leaving groups increase the rates of SM1 reactions.

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23
Q

When do SN2 reactions occur?

A

There has to be a strong nucleophile and a non-sterically hindered reactant. The nucleophile attacks the molecule from the back, forming a trigonal bipyramidal transition state. These reaction are more likely to occur in polar aprotic solvents.

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24
Q

Describe the kinetics of SN2 reactions.

A

SN2 reactions are second order.

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25
Q

How do SN1 reactions affect stereochemistry?

A

The reaction involves planar and achiral carbocation intermediates, meaning that the nucleophile may attack either side. Therefore, a Racemic mixture would be produced from optically active compounds.

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26
Q

When are SN1 reactions favored?

A

SN1 reactions are more likely to occur in polar protic solvents and with the use of bulky nucleophiles.

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27
Q

What reactions do alkenes undergo?

A 
Free Radical Halogenation
Combustion
Pyrolysis
SN1
SN2
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28
Q

Which reactions synthesize alkanes?

A 
Catalytic Hydrogenation (H2 and Pt or Ni)
Reaction of Lithium dialkyl cuprate and an alkyl halide
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29
Q

How do terminal alkenes differ from internal alkenes?

A

Terminal alkenes have a lower boiling point compare to internal alkenes. Terminal alkenes can be separated by fractional distillation.

30
Q

How do the properties of trans and is alkenes differ?

A

Trans alkenes have higher melting points and lower boiling points than cis alkenes because they have higher symmetry and are less polar.

31
Q

What reactions synthesize alkenes?

A

Elimination reactions using alcohols or alkyl halides
E1 —> difficult to direct b/w SN1 —> favored by highly polar solvents, highly branched carbon chains, good leaving groups, and low [weak nucleophiles]
E2 —> steric hindrance does not limit and strong bases favor E2

32
Q

What are the reactions that use alkenes as the substrates?

A 
Reduction - catalytic hydrogenation
Electrophilic Addition
• Addition of HX
• Addition of X2
• Addition of H2O
Free Radical Additions
Hydroboration
Oxidation
• Potassium Permanganate 
• Ozonolysis
• Peroxycarboxylic Acids
Polymerization
33
Q

Markovnikov’s Rule

A

The most substituted carbon in a double bond will usually receive the addition.

34
Q

Which reactions yield anti-Markovnikov products?

A

Free-radical additions

Hydroboration

35
Q

Which reactions synthesize alkynes?

A

Elimination through high heat and strong base of geminal or vicinal dihalides
Adding an existing triple bond to a carbon skeleton with n-BuLi and a strong base

36
Q

What reactions do alkynes undergo?

A 
Reduction (Lindlar's Catalyst for cis and Na, NH3 for trans)
Addition
• Electrophilic
• Free Radical
Hydroboroation
• Keto-enol tautomerism when vinylic borane intermediate cleaved with H2O2
Oxidation
• KMnO4, H+
• 1) O3 2) H2O
37
Q

What are aromatic compounds?

A

Unusually stable ring stems with delocalized electron density in Pi electron clouds.

38
Q

Alipathic

A

Non-aromatic compounds

39
Q

Hückel’s Rule

A

An indicator of aromaticity: 4n+2 pi electrons

40
Q

Antiaromatic

A

Cyclic, destabilized, conjugated polyene with 4n pi electrons

41
Q

What are the reactions that Benzene rings undergo?

A 
Electrophilic Aromatic Substitution
• Halogenation
• Sulfonation
• Nitration
• Friedel- Crafts Acylation Reactions
Catalytic Reduction
42
Q

How do the substituents affect reactions with the Benzene rings?

A

Activating ortho/para substituents are electron donating: NH2, NR2, NHCOR, OR, OCOR, and R
Deactivating ortho/para substituents that are weakly electron withdrawing: F, Cl, Br, and I
Deactivating, meta substituents that are electron withdrawing: NO2, SO3H, carbonyl compounds (COOH, COOR, COR, and CHO)

43
Q

What happens to the acidity of phenol as more alkyl groups are added?

A

The acidity decreases because electron-donating alkyl groups destabilize the all oxide anion.

44
Q

What are the key reaction mechanisms of alcohols and ethers?

A

SN1, SN2: Nucleophilic Substitution
Electrophilic Addition to the double bond
Nucleophilic Addition to a Carbonyl

45
Q

Which reactions could lead to alcohol synthesis?

A

Addition if water to double bonds
Addition if organometallic compounds to carbonyl groups
SN1 and SN2
Reduction of aldehydes, ketones, carboxylate acids, and esters using lithium aluminum hydride and sodium borohydrides (LiAlH4 will reduce carboxylic acids and esters, but NaBH4 will not)
Phenol synthesis from arylsulfonic acids with hot NaOH or from hydrolysis if diazinon salts

46
Q

How do you make -OH into a better leaving group?

A

Protonated it (good for SN1)
Convert it to a tosylate (good for SN2)
Form an inorganic ester (good for SN2)

47
Q

Which reactions do alcohols undergo?

A

Elimination Reactions
Substitution Reactions
Oxidation Reactions
• PCC converts 1° alcohols to aldehydes and 2° alcohols to ketones
• alkali (sodium or potassium) dichromate salt oxidizes 1° alcohols to carboxylic acids and 2° alcohols to ketones
• Jones Reagent (chromium trioxide dissolve in dilute sulfuric acid and acetone) oxidizes 1° alcohols to carboxylic acids and 2° alcohols to ketones
• Treating phenols with oxidizing reagents forms quinones
• KMnO4 will oxidize all the way to carboxylic acids

48
Q

What are the physical properties of ether?

A

Ethers are double substituted water molecules that boil at temperatures similar to that of alkanes. They are only slightly soluble in water and are inert to most organic reagents.

49
Q

How do you synthesize ethers?

A

Williamson Ether Synthesis: SN2 reaction that involves metal alkoxides with primary alkyl halides or tosylates. This could also be applied to phenols. Alkoxides only attack non hindered halides.
Cyclic ethers form from internal SN2 displacement and oxidation of an alkene by m-chloroperoxybenzoic acid.

50
Q

Which reactions do ethers undergo?

A

Peroxides are formed when the ethers react with the oxygen in the air.
Cleavage of straight chain ethers require vigorous conditions and either HBr or HI, proceeding with SN2 or SN1 conditions. (Acid catalyzed)
Peroxides undergo SN2 reactions, where the most substituted Carbon is attacked by the nucleophile. (Base or acid catalyzed [has a bit of SN1 and SN2 character], but base catalyzed cleavage has the most SN2 character so it attacks the last substitute nucleophile.)

51
Q

What are the physical properties of aldehyde and ketones?

A

Aldehydes and ketones have a dipole moment that could elevate boiling points, but not as high as alcohols.

52
Q

How do you synthesize ketones and aldehydes?

A

Oxidizing 1° alcohols to aldehydes (PCC)
Oxidizing 2° alcohols to ketones (sodium or potassium dichromate and Jones Reagent)
Alkene Ozonolysis
Friedel- Crafts Acylation

53
Q

Tautomers

A

Isomers that differ only in the placement of a proton

54
Q

Enolization

A

The interconversion between the keto an enol tautomers, where equilibrium lies on the keto side.

55
Q

What types of reactions do aldehydes and ketones undergo?

A

Michael Additions (SN2 to α,β-unsaturated carbonyl compounds)
Hydration to gem-diols (increase rate with a bit of acid or base)
Acetal and ketal formation when treated with alcohols catalyzed by anhydrous acid
Reactions with HCN
Condensation with ammonia derivatives (Nucleophilic substitution of carbonyl)
Aldol Condensation (aldehydes act as the nucleophile and substrate when mixed with a stronger base and higher temperatures, forming an α,β-unsaturated aldehyde that could lose an H2O to form a double bond when heated)
Wittig Reaction (converting C=O to C=C by using an ylide
Oxidation of aldehydes by KMnO4, CrO3, Ag2O, or H2O2 to form a carboxylic acid
Reducing aldehydes and ketones to alcohols with lithium aluminum hydride or sodium borohydride
Wolff-Kischner Reaction (complete reduction of aldehydes and ketones to alkanes by first converting the carbonyl to a hydrazine that releases N2 when heated with a base)
Clemmensen Reduction (Aldehyde and Ketone heated with amalgamated zinc in hydrochloric acid to form an alkane)

56
Q

What are the common names of the first six straight-chain terminal dicarboxylic acids?

A

Oxalic (ethanedioic) acid, malonic (propanedioic) acid, succinic (butanedioic) acid, glutaric (pentanedioic) acid, adipic (pentanedioic) acid, and pimelic (hexanedioic) acid

57
Q

What are the physical properties of carboxylic acids?

A

Carboxylic acids can form hydrogen bonds because they are polar, so they will have higher boiling points compared to similar alcohols. Deprotonated carboxylic acids have resonance structures that increase their stability, making them more acidic. Carboxylic acids with electron-withdrawing groups and resonance-stabililizing groups as substituents will be stronger acids. β-carboxylic acids are even more acidic due to the resonance structures that occur at the α-hydrogen. Dicarboxylic acis are more acidic than monocarboxylic acid, but the second proton is less acidic than that of a monocarboxylic acid.

58
Q

How do you synthesize carboxylic acids?

A

Oxidation of aldehydes, primary alcohols, and some alkylbenzenes by potassium permanganate
Grignard reagents (Mg and ether) that further react with carbon dioxide and water from tertiary alkyl halides, adding one carbon to the chain
Hydrolysis of Nitriles through SN2 reactions

59
Q

What reactions do carboxylic acids undergo?

A

Soap formation with NaOH
Nucleophilic Substitution
- Reduction with lithium aluminum hydride
- Ester formation through reactions with alcohols (where it occurs fastest for primary alcohols) that involves protonating the C=O bond, preparing the carbonyl carbon for nucleophilic attack, and causes the carbonyl OH to leave after being protonated
- Acyl Halide formation (usually with thionyl chloride or PBr3) [acid chlorides are super reactive because of the electron withdrawing chlorine]
Decarboxylation of 1,3-dicarboxylic acids and β-keto acids when heated, proceeding through a six-membered ring and forming carbon dioxide and an enol that tautomerizes to the keto form.

60
Q

What is the order of reactivity for carboxylic acid derivatives?

A

acyl halides > anhydrides > esters > amides

61
Q

What reaction synthesizes acyl halides?

A

Reacting carboxylic acids with thionyl chloride or PBr3

62
Q

What reactions do acyl halides undergo?

A

Nuclophilic acyl substitution
- Hydrolysis to carboxylic acids
- Ester conversion by reacting with alcohols
- Amide conversion
Friedel Crafts Acylation with benzene and AlCl3
Reduction to aldehydes with H2 and Pd/BaSo4 and Quinoline
Reduction to alcohols

63
Q

What reactions synthesize anhydrides?

A

Reacting an acid chloride with a carboxylate salt

Heating carboxylic acids to form five- and six-membered ring anhydrides

64
Q

What reactions do anhydrides undergo?

A

The leaving group tends to be a carboxylic acid
Hydrolysis to carboxylic acid
Amide conversion
Ester and carboxylic acid conversion by reacting with alcohols
Friedel-Crafts acylation

65
Q

What reactions synthesize amides?

A

Only primary and secondary amines can react with acid chlorides to form amides because a hydrogen must be lost. Acid anhydrides can react with ammonia to form amides, too.

66
Q

What reactions do amides undergo?

A

Hydrolysis under acidic conditions to form carboxylic acids
Hydrolysis in basic conditions to form carboxylates
Hofmann Rearrangement converts amides to primary amines by losing a carbonyl carbon, where the mechanism forms a nitrene that rearranges to form an isocyanate (using BrO-)
Reduction to amine with lithium aluminum hydride

67
Q

What reactions synthesize esters?

A

Ester = carboxylic acid + alcohol under acidic conditions

Acid chlorides/ anhydrides + alcohols

68
Q

What reactions do esters undergo?

A

Hydrolysis to carboxylic acids and alcohols under basic or acidic conditions
Saponification involves hydrolyzing fats (like triacylglycerol, which is an ester) under basic conditions to form soaps
Amide conversion
Transesterification that occurs when alcohols act as the nucleophiles that displace the alkoxy groups on esters
Grignard (RMgX) Addition to form ketones (which are more reactive than the esters unless the ketones have bulky alkyl groups) that could form tertiary alcohols with good yield when two equivalents used
Claisen Condensation (acetoacetic ester condensation) where the enolate ion of one ester attacks another ester, displacing the ethoxide ion and producing a β-keto ester

69
Q

What are phosphate esters?

A

Esters that have a phosphate in the backbone. These are important in biological processes.

70
Q

What physical properties do amines and nitrogen-containing compounds have?

A

Amines have boiling points between those of similar alkanes and alcohols. Since tertiary amines are unable to form hydrogen bonds, they have lower boiling points. Nitrogen inversion occurs (except at very low temperatures), so enantiomers of chiral nitrogens cannot be isolated. Amines are bases, where alkyl amines are more basic than ammonia, but less basic than hydroxide. Aromatic amines are less basic than alipathic amines

Reminder: electron-donating groups (-OH, -CH3, and -NH2) increases basicity and electron-withdrawing groups (NO2) reduce basicity

71
Q

What reactions synthesize amine compounds?

A

Alkylation of ammonia
- Direct alkylation of ammonia by reacting with alkyl halides
- Gabriel Synthesis converts a primary alkyl halide to a primary amine by using phtalimide (o-phthalic acid + ammonia reacting in KOH and ethanol), which is a good nucleophile, and NaOH/ water
Reduction
- From nitro compounds to primary amines using iron or zinc and dilute hydrochloric acid
- From nitriles to primary amines with Hydrogen and a catalyst or lithium aluminum hydride
- From amines through reductive amination (aldehyde or ketone reacts with ammonia, primary amine, or secondary amine to form a primary, secondary, or tertiary amine that will undergo hydride reduction (H2-Ni, Raney Nickel) in the presence of a catalyst
- From amides with lithium aluminum hydride

72
Q

What reaction do nitrogen containing compounds undergo?

A

Exhaustive Methylation (Hofmann Elimination) converts an amine to a quaternary ammonium iodide by treating with excess methyl iodide first, then silver oxide and water to ammonium hydroxide, which will be heated to undergo elimination to form an alkene and an amine. It will predominantly form the least-substituted alkene. Amine -> quaternary ammonium iodide -> ammonium hydroxide -> alkene + amine

MCAT: Biological Sciences (19 decks)

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