Organic Chemistry Flashcards
T/F: Esters have higher boiling points than carboxylic acids of similar molecular weight
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
T/F: Tertiary amides have a higher boiling point than primary amides of similar MW
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!
T/F: Carboxylic acids can only form 1 H bond with other carboxylic acids
FALSE
Can form 2 H bonds
T/F: Acyl halides, anhydrides, esters, aldehydes, and ketones are able to participate in H bonding
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)
According to IUPAC shit, what is the order of functional groups from most → least importance?
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”
What are the functional groups that can make H bonds with themselves, as well as with other molecules like water?
carboxylic acid
alcohol
amine
thiol (weak H bonds though)
ester suffix
-oate
How do you go from ketone → acetal?
ketone + 1 eq. OH → hemiacetal + 1 eq. OH → acetal
What is PCC? What does it convert 1° OHs to? 2° OHs?
weak oxidizing agent
1° OH → aldehyde
2° OH → ketone
What DECREASES the susceptibility of a Nu attack?
- 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
What is Na2Cr2O7? What does it convert 1° OHs to? 2° OHs?
strong oxidizing agent
1° OH → carboxylic acid (directly bypasses aldehyde)
2° OH → ketone
Among the acyl halides (F, Cl, Br, and I), which one would be the MOST reactive to nucleophilic substitution?
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
What are 4 well-known carboxylic acid derivatives?
acyl halides
anhydrides
esters
amides
Anhydrides are more reactive to Nu attack than carboxylic acids because:
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
polar aprotic vs protic solvents
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)
Rank the reactivity of carboxylic acid derivatives to Nu attack from most → least reactive
acid halides > anhydrides > esters/carboxylic acids > amides (because amide has resonance due to N = more stable)
T/F: H on α-carbons are generally most acidic in a molecule
TRUE
Hs on Cα are relatively acidic due to stabilization of negative charge on Cα after H removal from tautomerization (molecule → enol)
In a keto-enol tautomerization, is the enol or the keto form more favored at equilibrium?
keto
the carbonyl bond on the keto form is stronger than the C=C bond
What is the more stable configuration of the enolate in a keto-enol tautomerization: kinetic or thermodynamic form?
thermodynamic form
double bonds with more substituted carbons = more stable
In a keto-enol tautomerization, what forms quicker: the kinetic or thermodynamic form of the enolate?
kinetic form
kinetic form = less stable but forms more quickly due to LESS steric hindrance at the less substituted carbon during double bond formation
List the overall reaction, reactants, and (by)products of keto-enol tautomerization
RXN: aldehyde and ketones ↔ alcohols
reactants: aldehydes and ketones
products: enol (alcohol) form
List the overall reaction, reactants, and (by)products of amide hydrolysis
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
List the overall reaction, reactants, and (by)products of transesterification
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
List the overall reaction, reactants, and (by)products of esterification
RXN: carboxylic acid + alcohol → ester + H2O
reactants: carboxylic acid + alcohol
product: ester
byproduct: H2O
List the overall reaction, reactants, and (by)products of an aldol condensation. What happens if dehydration follows an aldol condensation?
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)
List the overall reaction, reactants, and (by)products of a retro aldol reaction
DECOMP RXN: 1 ß-hydroxycarbonyl molecule →H2O, OH-→ aldehyde/ketone + molecule with a carbonyl group
Reverse of aldol condensation
In IR spectroscopy, what do sharp peaks around 1700-1750 cm^-1 indicate?
presence of C=O group
In IR spectroscopy, what do sharp peaks around 3200-3500 cm^-1 indicate?
presence of -OH group (or a -NH group)
In IR spectroscopy, what do peaks around the leftmost part of the graph (4000-2500 cm^-1) indicate?
presence of hydrogen atoms
At around 3300 cm^-1, what are the two groups that show up? What do their peak(s) look like?
- OH group = broad peak
- NH group = narrow peak(s)
In IR spectroscopy, what do peaks around the middle part of the graph (2500-1000 cm^-1) indicate?
bonds w/o H atoms
SPECIFICALLY DOUBLE/TRIPLE BONDS
In IR spectroscopy, what do peaks around the rightmost part of the graph (1000 cm^-1 and less) indicate?
fingerprint region
If 2 spectra have different fingerprint regions, this means that they are spectra for two DIFFERENT molecules!!
In NMR, what does the downfield shift b/w 10-12 ppm indicate?
presence of H on CARBOXYLIC ACID groups!!
In NMR, what does the downfield shift b/w 8-10 ppm indicate?
presence of H on ALDEHYDE group
In NMR, what does the downfield shift b/w 6-8 ppm indicate?
AROMATIC Hs!
What makes a proton on the NMR designated as a singlet?
no Hs on carbon ADJACENT to proton in question!!
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.
TRUEEEEEEEEEEEE
For example, OH on carboxylic acid = singlet, but it is in the 10-12 ppm range
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.
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
What is the primary fxn of using paper chromatography vs thin layer chromatography (TLC)? List two similarities and differences between them
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
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
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
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
net charge molecule binding to column
- anion: negative (ie. COO-)
- cation: positive (ie. NH3+)
buffer used
- anion: pH > pI
- cation: pH < pI
What is the equation for retention factor (Rf)? If a molecule shows a higher Rf, what does this indicate about its polarity?
Rf = distance traveled by molecule / distance traveled by solvent (usually almost the whole TLC plate)
↑ Rf = ↑ nonpolar
What is the purpose of washing in extraction?
unwanted particles are washed away while desired compound remains in original solvent
Equation of efficiency of a column? What are 4 ways you can increase the efficiency of the column chromatography?
efficiency = length / width
↑ length
↓ width
↓ particle size
↓ column void volume (dead volume)
T/F: In reverse-phase chromatography, nonpolar molecules elute first
FALSE
Nonpolar molecules elute last because it binds more tightly on nonpolar stationary phase
What measurements are the quantitative results of high performance liquid chromatography (HPLC) based on? What does this measure?
peak area
measures the concentration of the compound
T/F: adding organic modifiers (ie. acetonitrile, methanol) maximizes hydrophobic interactions b/w protein + stationary phase in ion-exchange chromatography
FALSE
it MINIMIZES hydrophobic interactions by ↑ hydrophobicity of mobile phase → ↓ retentivity of peptides → proteins elute!
What does liquid-liquid extraction involve? Are the solvents it is used on miscible or immiscible?
involves ISOLATING a component from a mixture based on its relative solubility in 2 IMMISCIBLE solvents (diff polarities)
nonpolar or polar?
- hexane
- ethanol
- methanol
- acetone
- water
- diethyl ether
- hexane: nonpolar
- ethanol: polar
- methanol: nonpolar
- acetone: polar
- water: polar
- diethyl ether: nonpolar
equation of partition coefficient (K)
molarity in organic phase / molarity in aqueous phase
methanol vs water in terms of # H bonds it can make and bp
methanol vs water (in this order, respectively)
H bonds: 3 VS 2
bp: 65°C VS 100°C
Does acid-base extraction require 2 miscible or immiscible solvents to separate?
IMMISCIBLE
What is simple distillation used for? What compounds does it require?
used to separate liquids that boil < 150°C
requires compounds to have bps that differ by more than or equal to 25°C
What compounds can fractional distillation be used and for what? How does it do this?
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!
How and what is steam disillation used for and for what compounds?
uses steam to PURIFY tempearture-sensitive materials near 100°C
What could vacuum distillation be used for? How does it do this?
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
what does a gas chromatography do and for what?
separates compounds via an unreactive carrier gas passing through an adsorbant
What kind of compounds are compatible for gas chromatography in terms of MW, polarity, volatility (and hence bp), and thermal stability?
need compounds that readily vaporize w/o degradation
↓ MW and ↓ polarity → ↑ volatility = ↓ bp
thermally stable
What compounds can high-performance liquid chromatography (HPLC) be used for and for what?
can be used to analyze NONVOLATILE, THERMALLY UNSTABLE, COMPLEX compounds w/ accurate results
suitable for COMPLEX BIOLOGICAL SAMPLES
T/F: Paper chromatography can separate a complex mixture
FALSE
T/F: TLC is based on visual comparison/spot intensity and its less quantitative
TRUE
retardation factor equation
retention in mobile phase / retention in stationary phase
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
TRUE
↑ affinity = ↑ attraction = ↑ time to elute through (vise versa)
mass spectometry and gas chromatography is often combined together to do what?
calculate MW of the sample components
In liquid-liquid extraction, you can use carboxylic acids and amines. Exactly how?
carboxylic acids can be deprotonated using aqueous basic solutions (base wash)
amines can be protonated by using aqueous acidic solutions (acid wash)
T/F: mass spectrometry separates non-purified compounds by their mass-to-charge ratio
FALSE
THEY SEPARATE ALREADY PURIFIED COMPOUNDS!! (they may have been purified by methods such as gas chromatography)
anion vs cation exchange chromatography based on the net charge of molecule of interest and net charge of resin (stationary phase)
Net charge of molecule of interest
AEX: negative
CEX: positive
Net charge of resin
AEX: positive
CEX: negative
what would happen if you ↑ pH of mobile phase for CEX chromatography?
↓[H+] → ↓ net + charge on peptides → weaker binding of peptide to stationary phase → SHORTER retention times
