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MCAT > Organic Chemistry > Flashcards

Organic Chemistry Flashcards

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MCAT flashcards
1
Q

Highest-Priority Functional Group

A

the most oxidized carbon

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2
Q

Diols / Glycols

A

Alcohols with two hydroxyl groups

indicated by the suffix -diol

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3
Q

Diols with hydroxyl groups on the same carbon

A

Germinal Diols

aka hydrates

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4
Q

Diols with hydroxyl groups on adjacent carbons

A

Vicinal Diols

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5
Q

Aldehydes are named by replacing the -e of the parent alkane with …

A

-al

chain terminating carbonyl

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6
Q

What are the common names of the aldehydes methanal, ethanal, and propanal?

A

formaldehyde, acetaldehyde, and propionaldehyde

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7
Q

Ketones are named by replacing the -e of the parent alkane with …

A

-one

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8
Q

What is the most oxidized functional group that applies on the MCAT?

A

Carboxylic Acid

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9
Q

Carboxylic acids are named by replacing the -e of the parent alkane with …

A

-oic acid

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10
Q

Describe an ester.

A

Carboxylic acid derivative where the hydroxyl group is replaced with an alkoxy group (-OR; R= hydrocarbon chain)

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11
Q

Esters are named by replacing the -oic acid of the parent carboxylic acid with …

A

-oate

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12
Q

Describe an amide.

A

Carboxylic acid derivative where the hydroxyl group is replaced by an amino group (nitrogen-containing group).

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13
Q

Esters are named by replacing the -oic acid of the parent carboxylic acid with …

A

-amide

any substituents attached to the amino group are labeled with a capital N-

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14
Q

Describe an anhydride.

A

A dehydration reaction between two carboxylic acids

usually a cyclic molecule

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15
Q

The common names for the aldehydes and carboxylic acids that contain two carbons start with the prefix …

A

Acet-

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16
Q

What is the least similar of all the isomers?

A

Structural (Constitutional) Isomers

same formula but different connections

different chemical and physical properties

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17
Q

Stereoisomers

A

same atomic connectivity but different arrangement in space

conformational isomer: differ in rotation around a single sigma bond
configurational isomer: interconverted only by breaking a bond

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18
Q

Ring strain on cycloalkanes

A

Angle strain – bonded angles deviate from their ideal values

Torsional strain – cyclic molecules assume conformations that are eclipsed or gauche

Nonbonded strain (van der Waals repulsion) – nonadjacent atoms competing for the same space (steric hinderance in the flagpole interactions of the cyclohexane boat conformation)

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19
Q

Cyclohexane in a chair conformation

Hydrogen atoms perpendicular and parallel to the place of the ring called what, respectively?

A

perpendicular (up and down) = axial
parallel (sticking out) = equatorial

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20
Q

What are the two categories of configurational isomers?

A

Enantiomers and Diastereomers

both are optical isomers because the spatial arrangement of groups affects the rotation of plane-polarized light

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21
Q

Enantiomers

A

same connectivity but opposite configuration at EVERY chiral center in the molecule

nearly identical chemical and physical properties

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22
Q

Optical activity of enantiomers

A

rotates plane to the right (CW) = dextrorotary (+)
rotates plane to the left (CCW) = levorotary (-)

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23
Q

Optical activity in a racemic mixture of enantiomers?

A

(+) and (-) enantiomers present in equal concentrations

optical rotation cancels itself out so there is NO ROTATION OF PLANE-POLARIZED LIGHT

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24
Q

Diasteromers

A

occur when a molecule has two or some stereogenic centers and differs at some, but not all, of these centers

DIFFERENT CHEMICAL AND PHYSICAL PROPERTIES

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25
Q

A molecule has n chiral centers. How many possible stereoisomers are there?

A

2^n

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26
Q

Optical activity of enantiomers vs diastereomers

A

knowing the specific rotation of one diastereomer gives NO INDICATION on the specific rotation of another diastereomer

enantiomers ALWAYS have equal and opposite rotations

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27
Q

Meso Compound

A

a molecule with chiral centers BUT possesses an internal plane of symmetry

NO optical activity

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28
Q

(E) and (Z) forms of isomers

A

used for polyunsaturated double bonds

related from then highest priority substituent (highest atomic number) on each double bonded carbon

Z = SAME SIDE
E = OPPOSITE SIDE

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29
Q

Wedges vs dashes in Fischer projections

A

Wedges = project OUT from the plane of the page

Dashes = bonds going INTO the plane of the page

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30
Q

A molecular orbital is formed by a head-to-head or tail-to-tail overlap. What is the resulting bond?

A

sigma bond

all SINGLE BONDS are sigma bonds, accommodating two electrons

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31
Q

When two p-orbitals line up in a parallel fashion, their electron clouds overlap. What is the bonding molecular orbital called?

A

a pi bond

a pi bond on top an existing sigma bond is a DOUBLE BOND (two pi bonds for a triple bond)

NOTE: pi bonds cannot exist independently of a sigma bond; only when the sigma bond is formed do the p-orbitals of adjacent carbon become parallel and form the bond

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32
Q

Which is stronger, a sigma bond or a pi bond?

A

SIGMA BOND IS STRONGER

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33
Q

An element such as carbon has four equivalent sigma bonds. How is this possible since the valence electrons live in different subshells / orbitals?

A

Hybridization of the orbitals

Carbon actually has a stable 2sp^3 hybridized ground state

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34
Q

How do you predict H-NMR splitting patterns?

A

the n+1 rule

n = number of nonequivalent neighboring hydrogens

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35
Q

Oxidizing agents vs reducing agents.

A

Oxidizing agents: THEY THEMSELVES are reduced by oxidizing another agent

Reducing agents: THEY THEMSELVES are oxidized by reducing another agent

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36
Q

A Lewis acid is a what? What about a Lewis base?

A

Lewis Acid – electron acceptor in the formation of a covalent bond; vacant p-orbital; electrophiles
Lewis Base – electron donor in the formation of a covalent bond; lone pair of electrons; nucleophiles

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37
Q

Coordinate Covalent Bond

A

covalent bonds in which both electrons in the bond came from the same starting atom (the Lewis base)

comes from the interaction of Lewis acids and bases

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38
Q

Bronsted-Lowry acid? Bronsted-Lowry base?

A

acid – can donate a proton
base – can accept a proton

if the molecule can act as both a Bronsted-Lowry acid and base, it is AMPHOTERIC

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39
Q

The acid dissociation constant and pKa?

A

Ka = measures the strength of an acid in solution

Ka = [H+][A-] / [HA]

NOTE: pKa = -log(Ka)

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40
Q

What is special to note about alpha-hydrogens and acidity of functional groups?

A

the enol form of carbonyl-containing carbanions is stabilized by resonance

thus, these alpha-hydrogens are acidic and easily lost

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41
Q

Acidity increases with….

periodic table trend

A

decreasing bond strength and increasing electronegativity

when the trends oppose each other, BOND STRENGTH takes precedence

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42
Q

Nucleophiles

A

“nucleus-loving” species with wither lone pairs or pi bonds that can form new bonds

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43
Q

What is the technical definition between nucleophilicity and basicity?

A

Nucleophilicity – relative rate of reaction with an electrophile (KINETIC PROPERTY)
Basicity – related to equilibrium position of a reaction (THERMODYNAMIC PROPERTY)

44
Q

Effects of the following toward nucleophilicity:
Charge
Electronegativity
Steric Hindrance
Solvent

A

Charge – increases with increasing charge (negative charge)
Electronegativity – decreases with increasing electronegativity
Steric Hindrance – decreases with bulkier molecules
Solvent – protic solvents can decreases nucleophilicity by protonating the nucleophile or through hydrogen bonding

45
Q

Halogen nucleophilicity in polar protic solvent?

i.e. carboxylic acids, ammonia, water

A

nucleophilicity increases DOWN the periodic table
I- > Br- > Cl- > F-

weak acids, such as HF interact with the protons in solution and are less able to access the electrophile

46
Q

Leaving groups? When do they occur?

A

IF the electrophile DOESN’T have any empty orbitals, a good leaving group stability will increase the likelihood of a reaction

if empty orbitals are present, the nucleophile can bond without displacing the leaving group

47
Q

Leaving groups? What is the reaction functionally the opposite of?

A

molecular fragments that retain the electrons after heterolysis

OPPOSITE to coordinate covalent bond, since both electrons are given to one of the two products (heterolytic reaction)

48
Q

SN1 Reactions

A

Unimolar nucleophilic substitution reaction

1st Step (RATE LIMITING): The leaving group leaves, generating a positively-charged carbocation

2nd Step: Nucleophile attacks the carbocation

more substituted carbocation = more stable (alkyl groups stabilize the positive charge)

49
Q

SN1 Reaction Kinetics

A

rate of reaction depends ONLY on concentration of alkyl group containing the leaving group (substrate)

anything that accelerates the formation of the carbocation will increase the rate of the reaction

50
Q

SN1 Reaction KStereochemistry

A

reaction passes through a planar intermediate so it produces a RACEMIC MIXTURE

nucleophile can attack from either side

51
Q

SN1 Reaction Stereochemistry

A

reaction passes through a planar intermediate so it produces a RACEMIC MIXTURE

nucleophile can attack from either side

52
Q

SN2 Reactions

A

Bimolecular nucleophilic substitution reaction

ONLY STEP: nucleophile attacks the compound at the same time as the leaving group leaves (concerted reaction)

53
Q

SN2 Reaction Kinetics

A

nucleophile displaces the leaving group in a backside attack

nucleophile must be STRONG and the substrate cannot be sterically hindered

less substituted carbon is more reactive

concentration of the nucleophile and substrate BOTH determine the rate

54
Q

SN2 Reaction Stereochemistry

A

inversion of the relative configuration

if the nucleophile and leaving group have the same priority, this will result in a change in the absolute configuration (R) to (S) or vice-versa

55
Q

Oxidation state definition

A

indicator of the hypothetical charge an atom would have if all bonds were completely ionic

56
Q

How should you view oxidation and reduction in organic chemistry?

A

oxidation is increasing the number of bonds to oxygen or other heteroatoms (atoms other than carbon or hydrogen)

reduction is increasing the number of bonds to hydrogen

57
Q

Oxidizing agent

A

ACCEPTS an electron from another species so it is itself REDUCED

good oxidizing agents have a high affinity for electrons or unusually high oxidation states

58
Q

What do oxidizing agents often contain?

A

a metal bonded to a large number of oxygen atoms

59
Q

What do reducing agents often contain?

A

metals bonded to a large number of hydrides

60
Q

How are protecting groups typically removed?

A

an ACID WORKUP

61
Q

How are diols typically used in a reaction?

A

PROTECTING GROUP for a ketone

62
Q

Ortho, meta, para?

A

Ortho = groups on adjacent carbons
Meta = groups separated by one carbon
Para = groups are on opposite side of the ring

63
Q

What reactant produces aldehydes out of alcohols?

A

PCC

pyridinium chlorochromate

64
Q

What are aldehydes converted into with oxidizing agents?

A

germinal diols and then into carboxylic acids

65
Q

Jones oxidation

A

primary alcohol oxidized to a carboxylic acid by chromium trioxide

need acidic conditions in aqueous solution

CrO3

66
Q

What is a mesylate and tosylate?

A

react with hydroxyl group of alcohol to be a much better leaving group OR act as protecting groups for alcohols

mesylate is -SO3CH3 group

tosylate is -SO3C6H4CH3

67
Q

Alcohol role as protecting groups?

A

aldehydes or ketones can be reacted with two equivalents of an alcohol or diol, forming acetals (primary carbon with two -OR groups) or ketals (secondary carbon with two -OR groups)

68
Q

A phenol is oxidized to form a what? Then further oxidized to form?

A

phenol –> quinone –> hydroxyquinone

69
Q

In the presence of water, aldehydes and ketones react to form …

A

germinal diols (1,1-diols)

70
Q

An aldehyde or ketone is treated with one equivalent of an alcohol. The result is a …
What about two equivalents of an alcohol?

A

ONE = hemiacetal (basic conditions)
TWO = acetal (catalyzed under anhydrous acid conditions)

71
Q

Imine

A

compound with a nitrogen atom double-bonded to a carbon atom

simplest case – ammonia adds to the atom and water is lost (nucleophilic substitution)

72
Q

S hydrogen cyanide attacks a aldehyde or a ketone. The resulting product is called a …

A

cyanohydrin

HCN

73
Q

The two most common hydride reducing agents on the MCAT are

A

lithium aluminum hydride and sodium borohydride

LiAlH4 and NABH4

74
Q

Michael Addition reaction

A

carbanion attacks (made from alpha-hydrogen with strong base, LDA, KH, or OH) an alpha, beta-unsaturated carbonyl compound

75
Q

Kinematic vs thermodynamic products. Which is formed and when?
I.e. enolate formation

A

Kinetic product – formed rapidly but less stable (double bond to the less substituted alpha-carbon); formed in reactions that are rapid, irreversible, lower temperature, with a strong, sterically hindered base

Thermodynamic product – formed slowly due to steric hinderance but is more stable (double bond to the more substituted alpha-carbon); formed in reactions that are high temperature, slow, reversible, and weaker, smaller bases

76
Q

Amide formation from a carboxylic acid?

A

the nucleophile must be ammonia or another amine

77
Q

What reduction agent is strong enough to reduce carboxylic acids to a primary alcohol?

A

Lithium aluminum hydride

LiAlH4

78
Q

A chair conformation in which both substituents are both … will ALWAYS be more stable.

A

EQUATORIAL

NOT axial (more steric hinderance)

79
Q

cic-trans isomers of a subcategory of what isomer?

A

Diastereomer

non-mirror image stereoisomers

80
Q

Methylsulfonyl chloride?

A

a protecting group for ALCOHOLS; turns into mesylates

81
Q

What is the normal sp3 bond angle?

A

109.5 deg

82
Q

Transesterification

A

an alcohol acts as a nucleophile and displaces the esterifying group on an ester

83
Q

Strecker Synthesis

A

forms an amino acid from an ALDEHYDE

RACEMIC MIXTURE; BOTH L- AND D-AMINO ACIDS FORMED

aldehyde, ammonium chloride (NH4Cl), and potassium cyanide (KCN)

ammonia attacks after oxygen is protonated and forms an imine; CN- anion attacks forming a nitrile group; final product at end of step one is an aminonitrile (contains -NH4 and -CN)

in final step, two equivalents of water knock off the protonated nitrile carbon

84
Q

Characteristic wavenumber absorptions from IR spectrometry.

A

O-H: broad between 3300 and 3000 cm-1
N-H: sharp around 3300 cm-1
C=O: sharp 1700 cm-1

85
Q

What is the biggest piece of information we obtain from ultraviolet (UV) spectrometry?

A

wavelength of maximum absorbance – the extent of conjugation

conjugation up, lower energy of transition, greater the wavelength of maximum absorbance

86
Q

What does the magnitude of a H-NMR peak indicate?

A

the number of protons it contains

remember: equivalent hydrogens will resonate at the same frequency (same peak)

87
Q

Explain H-NMR deshielding?

A

the attached atom has other electronegative species that pull electron density away from the proton

this exposes the hydrogen (deshields) from the magnetic field leading to a LEFTWARD/DOWNFIELD shift (higher delta; higher ppm)

88
Q

How to determine spin-spin coupling (H-NMR)?

A

n+1 rule

if a proton has n protons that are on an adjacent atom (3 bonds away), it will be split into n+1 peaks

NOTE: DO NOT include protons attached to oxygen or nitrogen

89
Q

What is the chemical shift (ppm) downfield of an aromatic ring?

A

6.0-8.5

90
Q

How would we separate two products with similar boiling points?

A

fractional distillation

91
Q

Why would you use vacuum distillation over simple distillation?

A

if the product has a very high boiling point

using vacuum decreases the temperature required to reach the required vapor pressure (keeps product from being degraded)

92
Q

Retardation factor (Rf) equation from a TLC experiment

A

Rf = distance spot moved/distance solvent front moved

93
Q

Decarboxylation occurs with which molecules?

A

beta-keto acids and beta-dicarboxylic acids

94
Q

Sodium borohydride reduces carboxylic acids to …

A

TOO GENTILE to reduce carboxylic acids; NO CHANGE

95
Q

How do anhydrides, especially cyclic anhydrides, form?

A

SPONTANEOUSLY from dicarboxylic acids with HEAT

96
Q

IR spectroscopy is most useful for determining …

A

double and triple bonds

97
Q

What is the chemical shift associated with an aldehydic proton?

A

9 to 10 ppm

98
Q

Which isotopes are useless to use for NMR?

A

isotopes with no magnetic moment!

NOTE: nuclei with odd mass numbers or those with an even mass number but an odd atomic number will have a NONZERO magnetic moment

99
Q

Before absorbing an ultraviolet photon, electrons can be found in …

A

the highest occupied molecular orbit (HOMO)

it is excited to the lowest unoccupied molecular orbit (LUMO)

100
Q

IR spectrometry trend with higher order bonds?

A

higher-order bonds tend to have HIGHER absorption frequencies

note: conjugation and delocalization will shift the absorption frequency LOWER

101
Q

Wavenumber (v) is directly proportional to?
Inversely proportional to?

A

Directly: FREQUENCY
Inversely: WAVELENGTH

102
Q

Ina carboxylic acid, the absorption spectra for an -OH bond is shifted from 3300 cm-1 to about …

A

3000 cm-1

103
Q

What solvent should be used for a gravity filtration?

A

WARM or HOT

we want the desired product to remain soluble to be retained in the filtrate

if too cold, the product can precipitate and remain in the filter (residue)

104
Q

Hemiketal formation can be acid- or base-catalyzed. However, ketal formation MUST be …. catalyzed

A

has to be ACID catalyzed

acid protonates the hydroxyl oxygen to form a good leaving group (H2O)

the second alcohol then adds to the resonance stabilized carbocation

105
Q

How does the membrane of a neuron show select permeability?

A

the K+ channels are more “leaky” because there are more of them on the membrane

so, the membrane shows a select permeability of K+ over Na+

MCAT (6 decks)

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