CHM2211L Final Exam UF

Melting Point

temperature at which the solid phase is in equilibrium with the liquid phase

Pure Compound

sharp melting point, range is narrow (1-2 degrees)

Why does the presence of a soluble impurity in a sample has the effect of lowering and broadening the melting point range?

because the impurity disrupts the crystalline lattice of the sample so less energy is required to convert the solid phase into a liquid phase

What effects does insoluble impurity like sand and glass has on MP?

no effect

Errors of taking melting points:

1. improper amount of sample in capillary tube 2) mistaking sagging or shrinking sample as melting 3) presence of solvent cause crystals to "sweat"

Benzoic acid

122-123°C

Mandelic acid

120-122°C

An unknown compound was determined to be 74.97% C, 8.39% H, and no nitrogen. What is the empirical formula

100-74.97-8.39 = 16.64% O
# of C: 74.97/12 = 6.25/1.04 = 6
# of H: 8.39/1=8.39/1.04= 8
# of O: 16.64/16 = 1.04/1.04 = 1
EmF: C6H8O

Can IR spectroscopy be used to distinguish 2-pentanone from 2-hexanone? why or why not?

No because IR spectroscopy is used to distinguish functional groups presents on molecules. Both 2-p and 2-h contains the same functional group.

Acetophenetidin

analgesic and antipyretic (pain and fever relief)

p-acetamidophenol

Williamson ether synthesis

p-phenetidine

Amide synthesis

Recrystallization

solvent that will completely dissolve both desired compound and impurities when the solvent is hot; desire compound must be insoluble in the chosen solved at cold temperature and inorganic remains soluble when cooled

What do seed crystals do?

They serve as nucleation sites where more molecules of the desired compound deposit themselves in layers.

Explain the purpose of the hot gravity filtration. Why is it good to use the stemless funnel for this technique?

- Hot gravity filtration serves to remove any insoluble impurities that do not dissolve when the solution is brought to its boiling point.
- it is good to use the stemless funnel for this technique because this would minimize any contact between the hot solution and the funnel. If a funnel with stem is used the droplets of hot solution might get stuck on the stem inner surface and early crystallization of the solution might occur

ligroin

solvent derived from petroleum consisting of C7 and C8 hydrocarbon, non polar

Amide synthesis of acetophenetidin

p-phenetidine + acetic anhydride (solvent: Sodium acetate and hydrochloric acid)

Why is the sample of p-phenetidine reddish brown?

small amount of impurities caused by air oxidation of the amino functional group

how to remove reddish brown from p-phenetidine?

decolorizing carbon

Why should you not stir the crystals in the buchner funner?

this makes the filtration less efficient and does not adequately remove the solvent from the crystal

Williamson Ether Synthesis

1) p-acetamidophenol +sodium methoxide, methanol, and ethanol
2) 1st product (addition of sodium) + Bromoethane

Why does the williamson ether synthesis take two steps?

Because the hydrogen on the alcohol group of acetamidophenol would react with the bromoethane to create ethane and there would not be any reaction. The sodium acetate turns that alcohol group into a nucleophile that would attack the C of the bromoethane

Reflux condenser

Allows the reaction to be carried out at the boiling point of the solvent and yet it prevents loss of solvent or reagent due to evaporation. The vapors condense as they rise up the condenser and thus prevent them from escaping.

What was the best recrystallization solvent for the acetophenetidin?

Water because the solute is completely soluble at boiling point, but the crystals reappear when solution is placed in an ice bath.

Wooden applicator

helps with gentle boiling

Simple experiment that could be used to determine if the samples made through the two synthetic routes are identical:

If the sample made through two synthetic routes are identical, one can create a mixture from the same amount of two samples and the MP should be sharp and close to the recorded MP. If MP is lower than theoretical MP and has big range: samples are different from one another.

Why is HCl used instead of just DIW?

HCl is a much stronger acid which protonates the amine group of the p-phenetidin, which makes it more soluble in the solution

What is the purpose of the sodium acetate solution in the amide synthesis?

HCl protonates p-phenetidine and drives the reaction to the right but too much HCl would convert all of the compound to its conjugate acid and no reaction with acetic anhydride would occur. Sodium acetate creates a buffer within the reaction that would control HCl's acidity.

NMR of acetylphenetidin

N - 8ppm
CH3 (acetyl group) - 2ppm
H(2) (closer to N)- 7.4 ppm
H(2) (closer to O)- 6.8-7ppm
CH2 (closest to O)-4 ppm
CH3 (closet to O) - 1.4 ppm

Hexane vs water

immiscible (Hexane top)

Methylene chloride vs water

immiscible (Water top)

Ethanol vs. water

miscible

ether and water

immiscible (ether top)

Why is phenol much more acidic than cyclohexanol

There more stable or the weaker the conjugate base, the more acidic the compound is. When losing a proton, phenol's conjugate base has resonance stability from its double bond.

Could you separate 2,4-dinitrophenol (pH 3.96) from benzoic acid using extraction procedure IN THIS EXPERIMENT?

no since both are very close in acidity; cannot use reagents in this experiment to neutralize one and keep one (stronger acid) as a weak acid; both would be neutralized

What is extraction? What types are there?

Extraction is a technique that chemists use to remove selected components from a mixture. The different types are solid-liquid extraction and liquid-liquid extraction.

Why is carbon dioxide used as a solvent for solid-liquid extractions?

It offers a greener alternative to other solvents, it is readily available, nonflammable, nontoxic, and safe for the environment. Ease of removal of solvent at the end of procedure, and it is relatively quick.

What criteria must be met in order for a liquid-liquid extraction to be successful?

The two solvents that are chosen for the extraction must be immiscible. In addition, the compound to be extracted must have different affinities for the two solvents.

Treating NaOH vs NaHCO to the carboxylic-phenol mixture

NaOH is so strong that it would neutralized both strong acid such as carboxylic acid and weaker ones like phenol. On the other had NaHCO3 is weak enough that it can only react with strong carboxylic acid and remains unreacted with phenol

Carboxylate ions + HCl solution

this protonates carboxylate ions back into carboxylic acid compounds that forms solids when put in ice bath

If carboxylic compounds remain aqueous

use ETHER for back extraction

Phenol and Ether + BRINE

wash the organic layer - removing remaining water in solution

Anhydrous Magnesium Sulfate

The salt absorbs the water that is dissolved in the organic solvent.

What is present in the aqueous layer you drained? How do you neutralize it? How do you isolate it?

The carboxylate ion is present. In order to regenerate the carboxylic acid it must be added to HCl in an ice bath to induce crystallization. To isolate the crystals, vacuum filtration is performed.

What is present in the organic layer? What steps do you need to take to isolate the desired product?

The phenol is present. There may be some water present in the solution so it must be dried with brine and anhydrous magnesium sulfate until it no longer clumps together. The drying agent is then separated from the organic solution through gravity filtration. Once this is done, the ether must be evaporated under reduced pressure so that the pure phenol solid is left in the flask.

What is the difference between "extracting" and "washing"?

Extraction and washing can share very similar procedure but ultimately have different purposes. Extraction removes desire compounds/solutions from a mixture whereas washing filters out the impurities from the desired solution. Keep extraction and discard washed impurities.

Describe the practical reasons behind the direction of the flow of water through condenser:

Since the heated vapor from the distillation flask will travel from high to low, the water flows in the opposite direction in order to effectively cool the vapor which would liquify and flow down into the collection tube

Why is it important to soak the clover in water?

Since cloves are dried up, soaking them would allow water to penetrate into the cloves and more eugenol would be isolated.

Why is dichloromethane (CH2Cl2) added to the solution in the collection vessel? What process is this called?

To extract the eugenol from the water. This process is liquid-liquid extraction and the lower layer will be the dichloromethane along with the desired essential oil.

To dry the CH2Cl2:

brine and anhydrous magnesium sulfate

Major functional groups for eugenol

-OH group : 3517.6 (3600-3300)--10ppm
-OCH3 group: 2934 (3100-2700)--

Advantages and disadvantages of distillation vs. CO2 extraction:

with distillation, cloves are allowed to sit in water for full penetration which would be more advantageous because it would yield higher % of product. Extraction using CO2 reduces the chance of water remnant and impurities. CO2 extraction would produce better quality result; during the heating process of distillation, a lot of quality from the oil is evaporated

Is chlorophyll b more or less polar than chlorophyll a?

Chlorophyll b should be more polar than chlorophyll a because the former has a CHO group where the latter only has a CH3 group.

Which one is more polar? B-carotene vs. xanthophyll

xanthophyll would be more polar than B-carotene because of the -OH group at the ends of the molecules. B-carotene contains no oxygen and is quite non polar.

Ethyl acetate

polar solvent (-CO interaction)

Pencil for TLC plates?

the ink in the pen can tamper with the process; the ink would travel up the TLC plate with the solvent

Chromatography

techniques for separating, analyzing, and identifying compounds (column, thin layer, gas, high performance liquid)

Mobile phase

the eluent, the has or liquid phase in which the sample mixture is placed in

Stationary phase

a solid support that contains an adsorbent

If a component has a greater affinity for the stationary phase

travels more slowly

If a component has a greater affinity for the mobile phase

travels thought the stationary phase more quickly

Silica gel

has many sites for hydrogen bonding; polar compounds would interact with the silva and adsorb readily to the stationary phase

Rf value

distance from the origin to the center of the spot DIVIDED BY the distance form the origin to the solvent front; Polar compounds interacts more strongly with stationary phase and travel a shorter distance --> the more polar the compound, the smaller the Rf values

UV Light for TLC

UV lights activates a fluorescent indicator on the plates

Why is acetone used in chlorophyll extraction?

Acetone breaks down chlorophyll's lipid bonds to a plant's thylakoid structure and suspends the pigment in solution.

Why do we have to cover the test tube of acetone and spinach mixture with parafilm?

Acetone evaporates extremely quickly when interacting with air and all the solution would evaporate

What is the perfect composition of the eluent for the spinach lab?

50:50 hexane/ethyacetate

Why is a 50:50 ratio the best for this case?

Ethyl acetate is a polar compound while hexane is non polar; one compound interacts with the polar compounds of spinach while the other with the non polar compounds. The 50:50 ratio was enough to separate the polar and non polar compounds of the spinach, at the same time, the polar compounds also get to move up from the origin due to its interaction with the ethyl acetate. If only hexane was use, the chlorophyll a and b would remains at the origin and would not be separated form one another.

Why do we need to take pictures of TLC plates during lab?

because the compounds being separated will oxidize rapidly on exposure to air so it would fade away

Which pigment is the least polar which is the most?

B-carotene is the least polar and chlorophyll b is the most polar

What is the purpose of salicylamide?

an analgesic and antipyretic drug

Considering the directing effects of the substituents on salicylamide and predict the possible structures of the iodination products. Which do you think will be the major product?

-OH is an ELECTRON DONATING GROUP, the substituent would be directed to its para and ortho position. -NH2 is an ELECTRON WITHDRAWING GROUP and would direct the substituent to its meta position. The major projects has iodine at the ortho position to -OH and meta position to -NH2. (compare to the iodine group being para to the -OH)I think this would produce a higher % yield because the iodine group is being paced farther away from both functional groups which reduce the strain.

Electrophilic aromatic substitution

common reaction of benzene and its derivatives; two steps: 1) aromatic ring acts as a nucleophile and attack electrophile 2) aromatic ring is regenerated through the loss of proton

Charged intermediate species

stabilized by resonance

Why is iodine used instead of chlorine and bromine?

EAS with Cl2 and Br2 can occur in the presence of Lewis acid such as AlCl3, BUT iodine is the least reactive of the halogens

Green method for EAS:

iodination reactions using sodium iodine as the source of iodine and household bleach as an oxidizer (instead of nitric acid and I2)

What does absolute ethanol do to the salicylamide?

Dissolve the solid - use warmth of your hand to speed up dissolution

6% sodium hypochlorite solution (household bleach)

is an oxidizing agent that reacts with sodium iodine and turns it from a stable compound to a strong electrophile that would now react with the salicylamide in the electrophilic aromatic substitution

sodium thiosulfate

removes any residual iodine from the solution

1M hydrochloric acid

acidify the aqueous solution which drives the products to precipitates

IR Spectrum of Iodine at the ortho position to -OH

815.3cm-1

IR: -CO

1095.3

IR: -C=C

1621.6

IR: -NH2

3200-3300 (double peaks)

IR: -OH

3450.1

What is the directing effects of the substituents on salicylamide?

Major product gives the less strained position of Iodine that followings the directing effect of both substituent: meta to NH2 and ortho to OH

Interpret NMR:

H between I -NH2: 8.15 ppm (singlet)
H closer to I (between I and O): 7.7 ppm (doublet)
H closer to O (between I and O): 6.75ppm (doublet)

How would the Rf values change if a more polar solvent (like ethyl acetate) were used?

When a more polar solvent is used instead of non polar one like ligroin, it will interact more with the polar molecules and less with the non polar molecules causing a less dramatic separation. Rf values would be higher.

Why is it important not to dilute the initial sample before it has been loaded onto the chromatography column?

The more concentrated sample would produce a more significant or finer separation between polar and non polar compounds. Diluting the sample would cause a blurry separation between complex compounds instead of a fine separation

Which compound would elute first from the column: unreacted ferrocene, acetylferrocene, or diacetylferrocene? Why?

Non-polar or least polar compound elute first and therefore unreacted ferrocene elute first because it has no polar group. Acetylferrocene elute seconds because it only has 1 polar C=O group compared to diacetylferrocene which would elute last with 2 polar C=O groups.

Reaction of acetic an hydride

acetic anhydride reacts with phosphoric acid to form asylum ion which is an electrophile that can be used to add into an aromatic ring

Why is ferrocene called the super aromatic molecule?

it is about 10^5 times more reactive than benzene in electrophilic aromatic substitution because it consists of an iron atom sandwiched between two cyclopentadienyl anion

3M sodium hydroxide

neutralize the solution

TLC of acetylferrocene: eluent

methylene chloride

Why can you not introduce water into the chromatography column?

Water is very polar and should not be in the mix of the chromatography column. If water is present, it would interact with the acetylferrocene and diacetylferrocene and the whole solution would travel down together with no separation

Why cant you allow the volume of solvent to go below the top of the adsorbent?

because the drop would dry out and channels can form in the packing material which leads to inappropriate, poor separation.

What is the goal of pipets full of ligroin after addition of crude sample of acetylferrocene?

To load the sample onto the top of the column

How to elute ferrocene?

use ligroin

More polar solvent that is used to elute acetylferrocene

70:30 ligroin:ethyl acetate

Solvent for diacetyl ferrocene:

pure ethyl acetate