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MCAT > Organic Chemistry > Flashcards

Organic Chemistry Flashcards

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MCAT flashcards
1
Q

T/F: Esters have higher boiling points than carboxylic acids of similar molecular weight

A

FALSE
Esters have LOWER boiling points because they cannot make ester-ester H bonds, unlike carboxylic acids which can make 2 H bonds with themselves

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2
Q

T/F: Tertiary amides have a higher boiling point than primary amides of similar MW

A

FALSE
Tertiary amides have LOWER boiling point because they are not bound to any H (ergo all 3 R groups) → cannot H bond
Primary amides have 2 H → can H bond → higher boiling point!

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3
Q

T/F: Carboxylic acids can only form 1 H bond with other carboxylic acids

A

FALSE

Can form 2 H bonds

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4
Q

T/F: Acyl halides, anhydrides, esters, aldehydes, and ketones are able to participate in H bonding

A

TRUE
Although they all CAN’T H bond with themselves, they can participate in H bonding as an H acceptor with other molecules (ie. water)

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5
Q

According to IUPAC shit, what is the order of functional groups from most → least importance?

A

carboxylic acid (-oic acid) > ester (-oate) > acyl halide (-oyl halide) > amide (-amide) > aldehyde (-al) > ketone (-one) > alcohol (-ol) > thiol (-thiol) > amine (-amine)

“CEHAM al-one-ol thiol-amine”

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6
Q

What are the functional groups that can make H bonds with themselves, as well as with other molecules like water?

A

carboxylic acid
alcohol
amine
thiol (weak H bonds though)

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7
Q

ester suffix

A

-oate

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8
Q

How do you go from ketone → acetal?

A

ketone + 1 eq. OH → hemiacetal + 1 eq. OH → acetal

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9
Q

What is PCC? What does it convert 1° OHs to? 2° OHs?

A

weak oxidizing agent
1° OH → aldehyde
2° OH → ketone

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10
Q

What DECREASES the susceptibility of a Nu attack?

A
  • increased steric hindrance (especially larger and bulkier groups located on the acyl side of carboxylic acid or carbonyl group in general) → blocks Nu attack
  • ketone has more steric hindrance than aldehyde
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11
Q

What is Na2Cr2O7? What does it convert 1° OHs to? 2° OHs?

A

strong oxidizing agent
1° OH → carboxylic acid (directly bypasses aldehyde)
2° OH → ketone

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12
Q

Among the acyl halides (F, Cl, Br, and I), which one would be the MOST reactive to nucleophilic substitution?

A

Iodine

Iodine has the biggest atomic radius → best at distributing negative charge over a greater area → more stable LG = better LG → MORE reactive acyl halide

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13
Q

What are 4 well-known carboxylic acid derivatives?

A

acyl halides
anhydrides
esters
amides

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14
Q

Anhydrides are more reactive to Nu attack than carboxylic acids because:

A

anhydride carbonyl carbons are near more electron-withdrawing groups (carbonyl carbons are close to 3 Os in anhydride > 2 Os in carboxylic acids)

Near more EWGs → stronger the e- will be pulled away from carbonyl C → ↑ partial positive charge on carbonyl C → ↑ reactivity to Nu attack

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15
Q

polar aprotic vs protic solvents

A

aprotic: CANNOT make H bonds because it has no molecules that are able to create protons in solution (ie. OH-)
protic: CAN make H bonds because it has molecules that are able to create protons in solution (ie. H2O)

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16
Q

Rank the reactivity of carboxylic acid derivatives to Nu attack from most → least reactive

A

acid halides > anhydrides > esters/carboxylic acids > amides (because amide has resonance due to N = more stable)

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17
Q

T/F: H on α-carbons are generally most acidic in a molecule

A

TRUE

Hs on Cα are relatively acidic due to stabilization of negative charge on Cα after H removal from tautomerization (molecule → enol)

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18
Q

In a keto-enol tautomerization, is the enol or the keto form more favored at equilibrium?

A

keto

the carbonyl bond on the keto form is stronger than the C=C bond

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19
Q

What is the more stable configuration of the enolate in a keto-enol tautomerization: kinetic or thermodynamic form?

A

thermodynamic form

double bonds with more substituted carbons = more stable

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20
Q

In a keto-enol tautomerization, what forms quicker: the kinetic or thermodynamic form of the enolate?

A

kinetic form

kinetic form = less stable but forms more quickly due to LESS steric hindrance at the less substituted carbon during double bond formation

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21
Q

List the overall reaction, reactants, and (by)products of keto-enol tautomerization

A

RXN: aldehyde and ketones ↔ alcohols

reactants: aldehydes and ketones
products: enol (alcohol) form

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22
Q

List the overall reaction, reactants, and (by)products of amide hydrolysis

A

RXN: amide →H2O→ carboxylic acid + amino group

reactants: amide + H2O (LP on O Nu attacks carbonyl carbon → nitrogen group leaves and is replaced with OH group)
products: R1-COOH + R2-NH2

this rxn uses base catalysis

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23
Q

List the overall reaction, reactants, and (by)products of transesterification

A

RXN: R-ester + R’-OH ↔acid/base↔ R’-ester + R-OH

reactants: ester + alcohol
product: another ester (rxnts and pdts exchange R groups basically)
Byproduct: Nucleophile/an alcohol molecule

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24
Q

List the overall reaction, reactants, and (by)products of esterification

A

RXN: carboxylic acid + alcohol → ester + H2O

reactants: carboxylic acid + alcohol
product: ester
byproduct: H2O

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25
Q

List the overall reaction, reactants, and (by)products of an aldol condensation. What happens if dehydration follows an aldol condensation?

A

SYNTHESIS RXN: combines aldehydes/ketones → 1 molecule w/ carbonyl group and OH

reactants: aldehydes and/or ketones
products: 1 ß-hydroxycarbonyl (C=O and -OH) molecule

dehydration removes hydroxyl group → double bond + H2O (bypdt)

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26
Q

List the overall reaction, reactants, and (by)products of a retro aldol reaction

A

DECOMP RXN: 1 ß-hydroxycarbonyl molecule →H2O, OH-→ aldehyde/ketone + molecule with a carbonyl group

Reverse of aldol condensation

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27
Q

In IR spectroscopy, what do sharp peaks around 1700-1750 cm^-1 indicate?

A

presence of C=O group

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28
Q

In IR spectroscopy, what do sharp peaks around 3200-3500 cm^-1 indicate?

A

presence of -OH group (or a -NH group)

29
Q

In IR spectroscopy, what do peaks around the leftmost part of the graph (4000-2500 cm^-1) indicate?

A

presence of hydrogen atoms

30
Q

At around 3300 cm^-1, what are the two groups that show up? What do their peak(s) look like?

A
  • OH group = broad peak

- NH group = narrow peak(s)

31
Q

In IR spectroscopy, what do peaks around the middle part of the graph (2500-1000 cm^-1) indicate?

A

bonds w/o H atoms

SPECIFICALLY DOUBLE/TRIPLE BONDS

32
Q

In IR spectroscopy, what do peaks around the rightmost part of the graph (1000 cm^-1 and less) indicate?

A

fingerprint region

If 2 spectra have different fingerprint regions, this means that they are spectra for two DIFFERENT molecules!!

33
Q

In NMR, what does the downfield shift b/w 10-12 ppm indicate?

A

presence of H on CARBOXYLIC ACID groups!!

34
Q

In NMR, what does the downfield shift b/w 8-10 ppm indicate?

A

presence of H on ALDEHYDE group

35
Q

In NMR, what does the downfield shift b/w 6-8 ppm indicate?

A

AROMATIC Hs!

36
Q

What makes a proton on the NMR designated as a singlet?

A

no Hs on carbon ADJACENT to proton in question!!

37
Q

T/F: In NMR, any protons on electronegative atoms such as O or N are automatically considered singlets, but the ppm of these protons differ based on which group it is located in.

A

TRUEEEEEEEEEEEE

For example, OH on carboxylic acid = singlet, but it is in the 10-12 ppm range

38
Q

T/F: The TMS peak is at 0 in the NMR because it is just a reference peak. But we do count this peak when counting for protons.

A

FALSE

The first statement is true. Because it is true, we DO NOT count this peak when accounting for presence of protons in the NMR

39
Q

What is the primary fxn of using paper chromatography vs thin layer chromatography (TLC)? List two similarities and differences between them

A

FXN: characterize + analyze compounds

Similarities

  • polar stationary phase (water absorbed in paper, silica (glass) in TLC)
  • nonpolar mobile phase

Differences

  • TLC has BETTER separation than paper
  • TLC has rigid support whereas paper is fragile
40
Q

paper/TLC vs reverse-phase chromatography (RPC) in terms of stationary phase, mobile phase, and what primary interactions they are based on b/w mobile and stationary phase

A

stationary phase

  • paper/TLC: polar
  • RPC: nonpolar

mobile phase

  • paper/TLC: nonpolar
  • RPC: polar

based on what interactions b/w mobile and stationary phase

  • paper/TLC: hydrophilic
  • RPC: hydrophobic
41
Q

Ion-exchange chromatography has two types: anion and cation exchange. anion exchange vs cation exchange in terms of net charge of molecule binding to column and the pH the buffer used in comparison to the pI

A

net charge molecule binding to column

  • anion: negative (ie. COO-)
  • cation: positive (ie. NH3+)

buffer used

  • anion: pH > pI
  • cation: pH < pI
42
Q

What is the equation for retention factor (Rf)? If a molecule shows a higher Rf, what does this indicate about its polarity?

A

Rf = distance traveled by molecule / distance traveled by solvent (usually almost the whole TLC plate)

↑ Rf = ↑ nonpolar

43
Q

What is the purpose of washing in extraction?

A

unwanted particles are washed away while desired compound remains in original solvent

44
Q

Equation of efficiency of a column? What are 4 ways you can increase the efficiency of the column chromatography?

A

efficiency = length / width

↑ length
↓ width
↓ particle size
↓ column void volume (dead volume)

45
Q

T/F: In reverse-phase chromatography, nonpolar molecules elute first

A

FALSE

Nonpolar molecules elute last because it binds more tightly on nonpolar stationary phase

46
Q

What measurements are the quantitative results of high performance liquid chromatography (HPLC) based on? What does this measure?

A

peak area

measures the concentration of the compound

47
Q

T/F: adding organic modifiers (ie. acetonitrile, methanol) maximizes hydrophobic interactions b/w protein + stationary phase in ion-exchange chromatography

A

FALSE

it MINIMIZES hydrophobic interactions by ↑ hydrophobicity of mobile phase → ↓ retentivity of peptides → proteins elute!

48
Q

What does liquid-liquid extraction involve? Are the solvents it is used on miscible or immiscible?

A

involves ISOLATING a component from a mixture based on its relative solubility in 2 IMMISCIBLE solvents (diff polarities)

49
Q

nonpolar or polar?

  • hexane
  • ethanol
  • methanol
  • acetone
  • water
  • diethyl ether
A
  • hexane: nonpolar
  • ethanol: polar
  • methanol: nonpolar
  • acetone: polar
  • water: polar
  • diethyl ether: nonpolar
50
Q

equation of partition coefficient (K)

A

molarity in organic phase / molarity in aqueous phase

51
Q

methanol vs water in terms of # H bonds it can make and bp

A

methanol vs water (in this order, respectively)

H bonds: 3 VS 2

bp: 65°C VS 100°C

52
Q

Does acid-base extraction require 2 miscible or immiscible solvents to separate?

A

IMMISCIBLE

53
Q

What is simple distillation used for? What compounds does it require?

A

used to separate liquids that boil < 150°C

requires compounds to have bps that differ by more than or equal to 25°C

54
Q

What compounds can fractional distillation be used and for what? How does it do this?

A

can be used to separate MISCIBLE solvents that have a difference of bp < 25°C

involves heating to temps about 600°C, which could cause thermal cracking!

55
Q

How and what is steam disillation used for and for what compounds?

A

uses steam to PURIFY tempearture-sensitive materials near 100°C

56
Q

What could vacuum distillation be used for? How does it do this?

A

could be used to separate hydrocarbons that boil >380°C at normal pressure

lowers ambient pressure to temp at which liquid must reach to have sufficient vapor pressure to boil

57
Q

what does a gas chromatography do and for what?

A

separates compounds via an unreactive carrier gas passing through an adsorbant

58
Q

What kind of compounds are compatible for gas chromatography in terms of MW, polarity, volatility (and hence bp), and thermal stability?

A

need compounds that readily vaporize w/o degradation

↓ MW and ↓ polarity → ↑ volatility = ↓ bp

thermally stable

59
Q

What compounds can high-performance liquid chromatography (HPLC) be used for and for what?

A

can be used to analyze NONVOLATILE, THERMALLY UNSTABLE, COMPLEX compounds w/ accurate results

suitable for COMPLEX BIOLOGICAL SAMPLES

60
Q

T/F: Paper chromatography can separate a complex mixture

A

FALSE

61
Q

T/F: TLC is based on visual comparison/spot intensity and its less quantitative

A

TRUE

62
Q

retardation factor equation

A

retention in mobile phase / retention in stationary phase

63
Q

T/F: affinity of a compound to stationary phase is directly proportional to its attraction to the stationary phase, which is all directly proportional to the time it takes to elute through

A

TRUE

↑ affinity = ↑ attraction = ↑ time to elute through (vise versa)

64
Q

mass spectometry and gas chromatography is often combined together to do what?

A

calculate MW of the sample components

65
Q

In liquid-liquid extraction, you can use carboxylic acids and amines. Exactly how?

A

carboxylic acids can be deprotonated using aqueous basic solutions (base wash)

amines can be protonated by using aqueous acidic solutions (acid wash)

66
Q

T/F: mass spectrometry separates non-purified compounds by their mass-to-charge ratio

A

FALSE

THEY SEPARATE ALREADY PURIFIED COMPOUNDS!! (they may have been purified by methods such as gas chromatography)

67
Q

anion vs cation exchange chromatography based on the net charge of molecule of interest and net charge of resin (stationary phase)

A

Net charge of molecule of interest
AEX: negative
CEX: positive

Net charge of resin
AEX: positive
CEX: negative

68
Q

what would happen if you ↑ pH of mobile phase for CEX chromatography?

A

↓[H+] → ↓ net + charge on peptides → weaker binding of peptide to stationary phase → SHORTER retention times

MCAT (6 decks)

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