Ochem Final Exam

TLC visualization for Limonene

-the plate is treated with the strong oxidizing agent KMnO4 because non-aromatic alkenes are reactive with KMnO4 -a color change from the purple of KMnO4 to the tan of MnO2 will show where on the plate an oxidation reaction happened -the elute is 100% hexanes (very nonpolar, what the TLC plate is submerged in) -after the plate is ran in the elute, dip it into the KMnO4 -then hold the plate over a hot plate and heat the plate until it dries (it will be a paler purple)

separating the two layers after steam distillation

after the distillate is created, transfer the distillate to a separatory funnel in order to separate the two layers -the lower aqueous layer should be carefully drained and discarded -the organic layer should be drained or pipetted into a conical vial or snap-cap vial and a small amount of sodium sulfate should be added

Rf value

how far the spot traveled from the start line (Dx) How far the spot could've traveled, start line to end line (Do) Rf value = Dx/Do unitless number watch sig figs nonpolar compounds tend to have higher Rf values than polar compounds always measure from the spot line to the center of the dot solvent front distance= the measurement from the top to the bottom pencil lines (the space you're working on the plate) must be between 0 and 1 it is crucial to list the eluent used when reporting an Rf value because the Rf value will change with the polarity of the eluent Rf values are not intrinsic physical properties

% of transmittance (IR spectrum)

how much radiation was not absorbed is usually shown on the vertical axis strong absorptions are deep valleys in this format

chromatography of plant leaves

how the pigments are separated from each other order of elution from top of TLC plate to bottom: -beta-carotene: yellow -pheophytins: grey -chlorophylls: greens -xanthophylls: yellow exempting the xanthophylls, on the final plate you can assign up to two spots in a single lane as the same pigments, based on similar color and Rf values

Bonds between the same elements are usually nonpolar though exceptions exist

if one carbon is electron deficient because of nearby electron withdrawing groups, a dipole may exist even between two carbon atoms Also, the hydrocarbon portion of an aromatic ring is nonpolar, but the ring may be slightly more polar than a linear hydrocarbon due to effects from circulating pi electrons

enantiomers (and how to draw them)

isomers that are mirror images of each other (S) (S) --> (R) (R) when drawing the enantiomer of a compound you can draw the mirror image or just flip the stereochemistry (wedge to dash or dash to wedge)

What are some potential hazards to keep in mind when working with benzil?

it is a skin, eye, and respiratory irritant

sodium borohydride is stereoselective

it prefers a less hindered (crowded) approach to a carbonyl, where a choice exists -use experimental data to assess the isomer outcome

wave numbers

the number of waves that fit into a term-30centimeter the more waves that you can fit into one cm the shorter the wavelength and the higher the energy higher wave energy = higher energy infrared

Using the data you obtained in lab, calculate the percent yield of your benzil reduction experiment. Show all work! Hint: Each unit of NaBH4 has 4 hydride ions and it takes 2 moles of hydride ions to make one mole of product.

*work shown in image saved on desktop

sodium borohydride (NaBH4)

-a mild and selective reducing agent -in alcohol solution it reduces aldehydes and ketones to primary and secondary alcohols respectively -can reduce imines to amines but it does not react with esters, amides, acids or other carboxylic acid derivatives -a strong hydride reducing agent such as LiAlH4 must be used for carboxylic acid derivatives

UV visualization on TLC plate

-the TLC plates have a small amount of fluorescent material, allows then to glow under short wave UV light -if the solute on the plate also absorbs UV light, the plate will be dark where the solute is -molecules that absorb short wave UV light have an aromatic structure

Infrared spectroscopy

-bonds in organic molecules vibrate (in stretching and bending modes) at frequencies in the infrared region of the electromagnetic spectrum

chlorophyll

-characteristic green of plant leaves -the molecule responsible for turning light into energy for the plant -have an aromatic ring (aromatic rings can sometimes look different than simply a plain benzene ring) around a magnesium ion -key drivers of photosynthesis

IR radiation causes bonds to vibrate and not individual atoms

-different bonds absorb/vibrate at different frequencies and this is used for identification -a bond can do more than one type of vibration ex: C-H stretch is different than C-H bends

we may not see the same pigments before and after our extract is purified in column chromatography

-exposure to air and silica can cause reactions that would not occur within the cellular membrane -air can cause oxidation of the pigments -silica, which is slightly acidic, can also strip the magnesium ion out of the chlorophyll, generating pheophytin instead

cell membranes

-have a hydrophobic core (hydrocarbon core) - membranes enclose organelles such as chloroplasts which harvest light energy in plants -therefore, most pigments are non polar, because they are housed in the cell membrane

meso compounds

-have chiral centers -overall molecule is achiral -have internal plane of symmetry -not optically active

In response to the "nudge" of the infrared radiation, the organic molecules vibrate

-molecules can absorb this infrared causing them to vibrate and move around more than they already are -bonds can stretch in response to IR and bend (these show up as two different peaks on the IR) ex: C-H stretch and C-H bend -stretching or bending/ how the molecules vibrate depends on the type of energy (this is why bonds show up differently on the IR spectrum) and what the molecule is

KMnO4 visualization on a TLC plate

-non aromatic molecules don't show up under UV light -many functional groups will react with KMnO4 and undergo oxidation -KMnO4 (which is purple) will be reduced to MnO2 (which is brown) -our plate is bright purple except where a reactive solute is located, where we will see a yellow or tan spot functional groups that can react with KMnO4: -alcohols (not phenols) -aldehydes -alkynes -alkenes -benzylic carbons

benzil reduction reaction

-organic synthesis reaction where one function group is converted into another -benzil (containing two ketones) is reacted with NaBH4 (in ethanol solution) to form hydrobenzoin (containing two alcohol groups) -hydrobenzoin product could be 1 meso form or the racemic mixture of enantiomers (pg. 13) the two carbonyl reductions are sequential: first one carbonyl reacts, then the other does -both reductions make a new chirality center

Thin layer chromatography (TLC)

-runs upwards letting solvents wick up a plate that has a layer of particles stuck to it the materials are given the chance to stick on a stationary phase or travel with a mobile phase -stationary phase is polar (silica- more polar than organic molecules) -organic liquids (non polar) are used for the mobile phase the solutes choose between sticking to the polar stationary phase or traveling with a relatively nonpolar solvent a molecule with relatively few/ small dipoles will stick less than a solute with greater overall molecular polarity comparing solutes, the less polar solute will travel farther (spot to spot comparison or lane to lane comparison on a single plate) comparing solvents, the less polar solvent will move all spots less- because there would be less interaction of the plate with the mobile phase (plate to plate comparison)

Steam distillation

-the type of distillation we use is steam distillation -we will leverage the vapor pressure of limonene to purify it by distillation -steam distillation is a good method to isolate mid-sized molecules with very high boiling points that could decompose before reaching their boiling point -steam created by co-distilling water raises the total vapor pressure so that the system boils at a moderate temperature -small amounts of the organic material come over with the steam -limonene is nonpolar so it separates from water after the vapor is condensed and collected as distillate -water is added to the sample -essential oil and water come out/go through the apparatus together: it co-distills -we will eventually remove the H2O, you can separate layers after because limonene is non polar and water is polar (so oil is on the top of water) -the stream has vapor pressure and helps drive the desired vapors (limonene) which uses less heat which allows our sample to not burn and decompose

round bottom flask

-used in distillation -provides relatively even heating and mixing for solutions -placed into a heating mantle which is plugged into a voltage regulator such as a PowerMite so that the level of heating can be adjusted carefully

liquid-liquid extraction

-used when the mixture being separated is already dissolved in a solvent -based on the fact that some solutes are somewhat soluble in both water and organic liquids -most organic solvents have a low solubility in water so a liquid bilayer forms when a dissolved solute has only moderate solubility in its initial solvent we can add a second, more compatible solvent that will not mix with the first solvent. the solute will partition (distribute itself) between both solvents. the extent to which a solute migrates into the new solvent is an equilibrium that depends on the solute's relative solubilities in the solvents. most solutes will continue to be present in both layers after one round of extraction. To extract a solute fully, we extract multiple times with fresh batches of extracting solvent -we can accelerate the partitioning process by agitating the bilayer system. can be shaken in a capped centrifuge tube (open cap to vent vapors every once and a while- pressure will build up)

filtration to recover a solid

-we use vacuum filtration where an Erlenmeyer flask with a side arm for a vacuum hose is clamped onto a ring stand and a Hirsch funnel is used to separate the solid from the liquid filtrate: the liquid that passes through the filter

How many isoprene units are present in a monoterpene?

2

What is the maximum volume we can safely distill from a 500-mL round-bottom flask?

250mL

How many different stereoisomers of hydrobenzoin exist?

3

After the nucleophilic addition takes place, how many intermediate structures are involved before the final product?

3 intermediate structures are involved before the final product after nucleophilic addition takes place

IR spectrum graph

A print out of absorbance (y) or transmittance (y) based on wave number, cm-1 (x)the spectrum shows relative strengths of absorption on the vertical axis vs energy of radiation on the horizontal axis

In the article about rosemary, what do the authors propose rosemary essential oil might be useful for?

According to the article, rosemary is a useful antifungal remedy.

Would an acid-base extraction have been a good technique for obtaining limonene from the blended orange material? Briefly explain why or why not.

An acid-base extraction would not have been a good technique for obtaining limonene from the blended orange material. Limonene does not have acidic or basic functional groups (a carboxylic acid or an amine) so it doesn't act as a base or an acid and therefore a Bronsted-Lowry proton transfer reaction does not occur, so the extraction would not take place.

Provide a reasonable explanation for why a substance such as limonene is less dense than a substance such as water. Be specific.

Because water has stronger intermolecular forces. This causes the molecules to pack more tightly

Briefly and in your own words, describe how the process of distillation works.

Distillation is a technique used to purify liquids based on the liquids' different boiling points. Liquids with lower boiling points will distill at higher rates, while liquids with higher boiling points will distill at lower rates. In order to perform a distillation, a distillation apparatus needs to be set up where you have a sample with water added to it and as this mixture gets heated up, co-distillation will occur where the oil and water will move through the apparatus together. The steam of the water will help drive the desired vapors (the limonene in our lab) by vapor pressure. This allows the sample to not burn or decompose. The condenser then cools the vapor with an outer sleeve of cold water and the distillate is then collected into the receiver flask. After distillation, a separatory funnel can be used to separate the oil from the water. *did make a note about putting the answer more in my own words

Concerning the aspirin mechanism, indicate which compound is the nucleophile and which compound is the electrophile

Electrophiles are electron acceptors while nucleophiles are electron donors. Electrophiles accept electrons because they are either positively charged or they have empty valence shells.

Of all the experiments we've done so far (in person or virtually), which one does the benzil reduction seem most similar to?

Experiment 1

What are some of the hazards associated with limonene?

Flammable. It can cause skin irritation or an allergic reaction, and is irritating on contact with eyes. Serious damage to lungs may occur if limonene is aspirated or inhaled.

Match each of the compounds you mentioned for caraway in question 2 to the corresponding spots on the TLC plate. You will need to consider polarity as well as which visualization methods work to visualize which types of compounds. You may also wish to reconsider your choices for question 2 after trying to do the matching.

For the TLC plate of caraway, there is only one aromatic molecule and that is dillapiole, therefore it will have to be the spot that traveled 2.6 cm because it is the only spot that was able to be visualized using UV light visualization. It's also an alkene making it KMnO4 reactive. The spot that traveled a distance of 3.6 cm would have to be limonene as it is more non-polar than dillapiole, not an aromatic so it is not visualized by UV light and is an alkene, so it is KMnO4 reactive. The spot that traveled a distance of 1.7 cm would be carvone because it has a polar carbonyl functional group, making it more polar than dillapiole that contains ether functional groups. Carvone is not an aromatic compound so it cannot be visualized by UV light, but it is an alkene, so it is reactive with KMnO4. Even though there is another compound, linalool, that has a polar alcohol group, linalool is only 3.7% of caraway while carvone is 55.2% making the appearance of carvone on the plate more likely than linalool.

For the anise TLC data, one of the compounds present should be visible using both UV and KMnO4 techniques (based on the structure of the compound and the functional groups present). However, this compound was observed only under the UV lamp (no visible yellow spot). After reading through the 3.Chemical Constituents section in the article above for anise, propose a reasonable explanation why no yellow spot is seen

For the anise TLC data, it is possible that a compound that should be visualized using both UV light and KMnO4 techniques, is only visible using UV light. Even though the proper functional groups are present within the compound, the percentages of that compound may be too low to be visualized on the TLC plate. As shown in the article, the studies done had different percentages of the compounds that made up the essential oil and used different extraction methods, which makes the TLC plate results vary. A yellow spot will not be visible on the TLC plate if the percentage of that compound is too low.

benzoin

intermediate product -has one chiral center

melting point analysis

Helps you to identify the solid a pure sample: matches the literature data and has a narrow melting point range impure sample: melting point range will be wide and lower literature data should always be a range: -record the first temperature when you see the first drop of liquid (T1) -record the second temperature when all of the solid has turned into liquid (T2) melting point range= T1 - T2 make sure to label it with degrees Celsius

The melting point of meso hydrobenzoin is 139-140 oC. The melting point of racemic hydrobenzoin is 122-123 oC. Indicate which isomer(s) of the product you made based on examination of your melting point data.

I made the meso hydrobenzoin because my melting point range was 124.1 degrees Celsius - 135.2 degrees Celsius. My melting point range was a lot wider and lower than the literature data of meso hydrobenzoin because my product wasn't as pure.

Describe how our experimental procedure would have been different if limonene were more dense than water.

If limonene was more dense than water, when the distillate of water and limonene was added to the separatory funnel, the limonene would be at the bottom of the funnel and the aqueous layer would be on the top. The limonene would then have to be carefully drained instead of pipetted out of the top of the separatory funnel.

In addition to naked eye, UV lamp, and KMnO4 stain, there are many other ways to visualize organic compounds on a TLC plate. Pick two of these visualization methods (aside from ones we've used) and briefly explain how each method could have provided useful additional information relevant to the TLC analysis of spices above.

In addition to the naked eye, UV lamp, and KMnO4, some other ways to visualize the organic compounds within the spices are phosphomolybdic acid stain and iodine. Phosphomolybdic acid stain would be a useful stain for extra identification as it is able to visualize a wide variety of compounds such as alcohols, alkenes, and many carbonyl compounds which are functional groups of multiple compounds within this lab. In addition, an iodine visualization method may be useful to narrow down which molecules showed up on the TLC plate as this method only visualizes aromatics.

Briefly explain the purpose of MgSO4 is in this procedure (spinach pigment lab)

MgSO4 is a drying agent so it is ground up with sand and the spinach leaves to form a homogenous powder. The drying agent is important because it removes trace amounts of water from the spinach leaf solution so the resulting spinach extract, after being spun down in the centrifuge, is more concentrated.

when the product is formed from a reaction with a carbonyl and NaBH4 or NaBD4 in D2O or H2O where do the H or D go?

NaBD4 or NaBH4 will be the extra H or D off of the chiral carbon D2O or H2O will create the -OH groups or the -OD groups off of the chiral carbon

Concerning the NaBH4 mechanism, indicate which compound is the nucleophile and which compound is the electrophile.

NaBH4 is the nucleophile and benzil is the electrophile in the NaBH4 mechanism

TLC plate of spinach pigments

On the initial TLC plate (where the one pigment extract is spotted), you should see no more than one spot each for beta-carotene, chlorophyll a and chlorophyll b -you can see up to three spots for xanthophylls After purification, you may see two slower0 running spots the color of beta-carotene and pairs of matching green spots for each chlorophyll -excepting the xanthophylls, on the final plate you can assign up to two spots in a single lane as the same pigment, based on the similar colors and Rf values

In the article about anise, the authors reviewed a substantial amount of information (this is called a "review" article) pertaining to various pharmacological properties of the Pimpinella anisum plant. Based on this information, list any four potential uses of this plant and/or its essential oil.

Potential uses for the Pimpinella anisum plant and/or its essential oil include use as an antibacterial and antifungal. It has anticonvulsant effects which delay the onset of seizures. Another use of Pimpinella anisum is as an antiulcer remedy to decrease gastric ulcers. Studies also showed that this essential oil has anti-inflammatory effects.

Briefly explain what makes silica gel such a polar material. Refer to specific structural features in your answer.

Silica gel is used to coat the TLC plates in order to form a stationary phase that is more polar than organic molecules and also used within column chromatography. Silica gel's chemical structure is SiO2 making it a polar molecule due to the electronegativity difference between silicon and oxygen being 1.7. At the surface of the silica gel the oxygen molecules have the potential to bind to protons to form hydroxyl groups which increases the polarity of the silica gel further, since silicon is double bonded to oxygen alone.

With respect to column chromatography, indicate why the silica gel was originally wetted with 100% hexanes, rather than 90% hexanes/10 % acetone or 70% hexanes/30% acetone.

Silica gel was originally wetted with 100% hexanes in order to create a homogenous environment for the pigments to travel through. When running column chromatography we want to change the liquid running through the column to form a gradient elution. Therefore we would use 100% hexanes first because it is the most non-polar (compared to the mixtures with acetone) so the mobile solutes, the most non-polar pigments in this case, will be recovered first while the polar pigments will stick to the polar silica gel. We would then add the 90% hexanes/10% acetone and 70% hexanes/30% respectively because acetone is a polar molecule, which will allow the polar molecules to then be separated out and all fractions can then be collected that very in polarity.

What is a specific advantage of steam distillation?

Steam distillation is able to isolate mid-sized molecules with very high boiling points that would otherwise decompose before reaching their boiling point. The steam is created by co-distilling water which raises the total vapor pressure so the system is able to boil at moderate temperatures and not overheat.

In the article about caraway seed, what do the authors propose dill essential oil might be useful for?

The authors concluded that dill essential oil is useful as an antibacterial and antifungal remedy (natural antimicrobial remedy).

Indicate which compound is the catalyst in the aspirin mechanism.

The catalyst is H3PO4 within the aspirin mechanism the catalyst is written over the arrow within the reaction and is not used up within the reaction (written on the left and right side of the reaction)

Indicate what lab technique/method was used to obtain the essential oils from cumin and rosemary.

The lab technique used to obtain the essential oils from cumin and rosemary was hydrodistillation.

When considering TLC analysis as described in the video, how does the polarity of a compound relate to the distance it travels on a TLC plate?

The more non-polar the compound the father it travels on the TLC plate. This is because the solvent is relatively non-polar so the non-polar compounds will want to travel with the non polar solvent, up the TLC plate.

Using your IR data, indicate the best and most obvious way to determine that the reactant (benzil) has been converted into the product (hydrobenzoin).

The most obvious way to determine that benzil has been converted to hydrobenzoin is by looking for the unique structural elements within the two very similar molecules. Benzil and hydrobenzoin differ by their carbonyl groups and alcohol groups. Hydrobenzoin does not have any carbonyl groups, so no carbonyl peaks within the IR should show up, only OH peaks should be present. For benzil, no OH peaks should be present on the IR, only carbonyl groups should be present. Therefore, if carbonyl peaks are present on the IR it is benzil and if OH peaks are present on the IR it is hydrobenzoin. *make sure to specify where the peaks show up on the IR spectrum

How many distinct mechanistic steps are involved in the aspirin mechanism?

There are five mechanistic steps within the aspirin mechanism: activation, nucleophilic addition, proton transfer, elimination, deprotonation -every set of arrows = a mechanistic step

Match each of the compounds you mentioned for cumin in question 1 to the corresponding spots on the TLC plate. You will need to consider polarity as well as which visualization methods work to visualize which types of compounds. You may also wish to reconsider your choices for question 1 after trying to do the matching.

Using the TLC data, the spot that traveled a distance of 3.0 cm and is activated by UV and KMnO4 would be cuminic alcohol because its alcohol group makes it the most polar molecule and therefore it traveled the shortest distance on the TLC plate. The molecule does contain an aromatic ring, so it is visualized by UV light and it contains an alcohol functional group, so it does react with KMnO4.The spot that traveled a distance of 3.7 cm, is visualized by UV light and reacts with KMnO4 would be cuminal because it is a more nonpolar molecule than cuminic alcohol. It also has an aromatic ring making the molecule visualizable with UV light and the aldehyde functional group is reactive to KMnO4. Lastly, the spot that traveled 4.3 cm would be gamma-terpinene because it is the most nonpolar molecule of the three and so it should travel the farthest up the TLC plate. It is a non-aromatic molecule, so it is not visualized by UV light. However, it is an alkene so it will react with KMnO4.

Briefly explain how you can use your TLC data to determine if your reaction was complete or incomplete.

You can use the TLC data to determine if your reaction was complete by seeing if the three different spots in the three lanes all traveled different distances. the three lanes are benzil (reactant), benzoin (intermediate), and hydrobenzoin (product). The benzil should be the spot that traveled that farthest distance because it is the most nonpolar since it doesn't have an alcohol groups. Benzoin should be the second farthest spot because it isn't as nonpolar as benzil since it has an alcohol group, but it still has a carbonyl group so it is less polar than hydrobenzoin. Hydrobenzoin should travel the shortest distance because it is the most polar due to it's two alcohol groups. The reaction would be incomplete if the spots on the TLC plate all traveled the same distance or if the last two spots where the same distance (this would indicate that the reaction stopped at the intermediate).

experimental specific rotation equation

[alpa]^20 = alpha observed / c * I -c = the concentration of solute in g/mL, grams of limonene/mL of solution -I= pathlength of the cell in decimeters (1 dm) -pure sample is 125.6 degrees (literature value) observed optical rotation is what is recorded from the polarimeter

the organic compounds within the spices (cumin, caraway, anise seed and rosemary) are not colorful so other visualization methods are needed...

a UV lamp can be used to visualize aromatic compounds -ex: benzene, toluene, caffeine, aspirin KMnO4 stain can be used to visualize compounds with certain functional groups -ex: alcohols, aldehydes, alkynes, alkenes, benzylic carbons (carbons off of benzylic ring, benzylic ring carbons don't show up)

polarity affects...

a wide range of properties such as... solubility melting point (more polar molecules typically have a higher melting point range) chromatography extractions

control

a test we run ourselves using a known material to validate our interpretation of results from test samples -sometimes our control can be a mixture, such as a starting mixture we are trying to separate

drying agents

a trace amount of water can interfere with isolation of an organic solute, the water acts as an impurity -when preparing to isolate an organic solute we may "dry" the liquid layer first if the organic solute was in contact with water beforehand -"drying" an organic solution means getting rid of trace water drying agents are certain salts that can absorb water while remaining solid by incorporating water molecules into cavities in their crystal lattices -the solid will clump up if it has absorbed water and the "dry" solution can then be decanted (poured away from the solid) to separate the solution from the solid don't add too much drying agent otherwise it will absorb the desired solute in spaces between the crystal grains

functional group region is easier to interpret

above 1400cm-1 the fingerprint region (below 1400 cm-1) can be complicated

beta-carotene

absorb light energy, but they pass that energy to a chlorophyll molecule in order for it to be used in photosynthesis

what molecules are visible under short-wave UV light on our TLC plates

aromatics -limonene is not aromatic so it will not be visible under UV light

What will the color of this reaction be at the beginning and at the end?

beginning=yellow because of benzil, end=colorless because hydrobenzoin is formed

TLC plate analysis for benzil, benzoin and product

benzil should've traveled the farthest on the plate: most non-polar benzoin: should be in the middle because it has one alcohol group and one carbonyl product should've traveled the least because it is the most polar due to alcohol groups

What is the name of the intermediate organic compound formed if this benzil reduction reaction does not go to completion?

benzoin

List the names of any 2 pigments in spinach leaves, other than chlorophylls.

beta-carotene and pheophytins are two of the pigments in spinach leaves

Indicate which chlorophyll pigment is more polar.

chlorophyll B cause it contains CH3-C=O (chlorophyll A contains a CH3 at that R group)

IR is a great tool to identify chemicals

depending on what type of bonds a molecule has it is going to react or absorb different places in the IR spectrum bonds vibrate in unique, characteristic ways

RF values (TLC plate analysis)

distance of the dot (cm)/ distance of the plate (cm) -shouldn't have a unit

it is important to note that an impurity may not be detectable by every test we can run

each test leverages a different aspect of molecular properties -it is routine to run multiple analytical tests for complete characterization because some impurities will show up by one method while other impurities will show up by different methods

Suppose the observed optical rotation of an organic compound was measured to be -27.6 o. Suppose 0.274 g of that compound was dissolved to make a 10 mL solution, and this solution was then placed into a polarimeter cell with I = 1. Calculate the experimental specific rotation of this compound.

experimental specific rotation = -27.6 degrees / (0.0274 g/mL)(1 dm) = -1007.3 degrees C = 0.274 g/ 10mL = 0.0274 g/mL

the intensity of bonds can be extremely variable

for example, a O-H bond has a weak, medium, and strong wave number portion depending on what the atoms are attached to (carboxylic acids, H-bonded, free)

why we use excess of NaBH4

full reduction of Benzil requires 2 molar equivalents of hydride -each NaBH4 can can theoretically provide 4 equivalents of hydride ion, but we can't utilize all 4 equivalents so we simply use an excess of NaBH4 to ensure complete reaction

pheophytins

have the same structure as chlorophylls but without the magnesium ions -two types a and b (just like chlorophyll) -typically appear grey on silica, but may be a very pale green in solution

hexanes and hexane mixtures used to perform column chromatography

hexanes is used to dissolve the spinach pigment residue on the sides of the beaker and to wet the column 90:10 mixture of hexanes and acetone will elute the beta carotene 70:30 hexanes and acetone mixture will be the most polar mobile phase (called an eluent) and will elute the most polar chlorophyll pigments

briefly explain what infrared spectroscopy is and how it works.

infrared spectroscopy is a way to find/observe the different types of bonds in a molecule. By using IR radiation, the molecule is able to absorb the radiation without breaking the bonds. The IR radiation makes the bonds vibrate in a unique way (even for stretching and bending of the same bond) and the different vibrations are recorded on an IR spectrum. The different vibrations are shown on the graph as different peaks

thylakoid membranes

inside chloroplasts, contain the pigments that harvest light energy

Limonene

is a monoterpene, having two isoprene skeletons in its structure -many flavors and fragrances from plants are terpenes -the fact that we can smell terpenes (like limonene) indicates they have vapor pressure

chromatography

is used to separate mixtures and characterize materials. It can tell us whether a material is pure or not and can purify the material

solid-liquid extraction

leaf material is ground up to free the pigments (from the cell membrane) for removal by solid-liquid extraction when we are trying to remove a soluble material from a blend of solids, not all of which are soluble the solids are crushed up to increase its surface area for better blending and enables the solutes to be extracted faster extract: liquid + solutes

nonpolar organic liquids tend to have...

low boiling points and high vapor pressures (need to cover our organic liquids to keep them from evaporating)

IR radiation

lower in energy than visible light, but higher in energy than microwaves and radio waves this is enough energy to cause bonds in organic molecules to vibrate but not enough energy to break bonds

percent recovery of limonene

mass of limonene obtained/ mass of orange peel X 100%

terpenes

naturally occurring organic molecules containing 5-carbon pieces called isoprene units -the parent structure isoprene appears repeatedly in terpenes, although the double bonds will be absent or in different locations terpenes are classified by the number of isoprene units they contain -monoterpenes have two isoprene units, sesquiterpenes have three, diterpenes have four

What lab technique is used to measure the optical rotation of an organic compound?

polarimetry

reactions with NaBH4 (what do the reactants contain and what does the product contain?) what functional groups cannot react with NaBH4?

reactant contains a carbonyl that is reduced to an alcohol NaBH4 doesn't react with esters or amides

Xanthophylls

similar core structures and color as carotenes -carotenes are hydrocarbons, but xanthophylls also possess polar bonds to oxygen atoms

most organic molecules are nonpolar

since C-H bonds have no significant dipole because of this many organic molecules have low solubility in water (very polar)

Select all potential hazards of working with hexanes.

skin and eye irritant flammable toxic if swallowed or released in the water supply causes dizziness, respiratory irritation, headache if vapors inhaled

Indicate the name of the overall method/process/technique for removing pigments from spinach leaves.

solid-liquid extraction spinach leaves were ground up with a mortar and pestle with sand and MnSO4, acetone was added to the centrifuge tube, shaken up (allowing for ventilation) and then placed in the centrifuge so that the liquid portion of the mixture would be at the top of the tube and the solid portion would be at the bottom. The liquid was then pipetted out, this is what contains the spinach pigments

My answer for "what is steam distillation/ what is distillation?"

steam distillation is a type of distillation that co-distills water and an organic material (such as limonene) and raises the vapor pressure of the system so that the system boils at a moderate temperature because on it's own, some organic liquids (like limonene) have very high boiling points and could decompose before reaching their boiling point. the steam has vapor pressure which helps move limonene and allows the use of less heat so limonene wont burn. So the vapor pressures of the system will then run through the distillation apparatus and will then be cooled within the condenser where cold water is running on the outside of the tube and then the liquid will be collected that contains water and the organic material. distillation on its own explains the process of vaporizing the liquid, cooling the vapor and then condensing the vapor into a liquid. it is a technique used to purify liquids.

diastereomers

stereoisomers that are not mirror images of each other (S) (R) --> (S) (S)

Distillation

technique used to purify liquids -big in alcohol industry: the more you distill, the more pure it is -within oil refining -within the cosmetic industry: perfumes, essential oils based on differences in boiling points (BP) -liquids will distill t different rates depending on BP -liquids with lower boiling points distills more quickly -liquids with higher boiling points distill slower involves vaporizing the liquid (such as by boiling), then cooling and condensing the vapor into a liquid that can be collected

intrinsic physical properties of materials

tested and validated properties inherent to a pure material such as density, molecular weight and physical state at standard conditions -when these are known you may not need a control in your experiment

optical activity

the ability of chiral molecules to rotate plane-polarized light measured by passing a single plane of light through a sample to test whether and how far the light was rotated by the sample the polarimeter passes a beam of light through a sample and encounters a second polarizing filter. the detector rotates until it observes a maximum throughput of light the sign and magnitude of rotation is the only output from a polarimeter extent of rotation depends on the number of chiral molecules in the beam, so the result must be standardized the number of molecules is dependent on the length of the sample tube and the concentration o the sample used, which is why these terms appear in the calculation of specific rotation "D"= the wavelength of light used in polarimetry measurements, which is the D line in the sodium atomic emission spectrum (589nm).

A bond is polar if..

the connected atoms differ in electronegativity a slight difference leads to a small bond dipole, while a large electronegativity difference yields a very polar bond

other pigments present in plant leaves

these other pigments absorb other wavelengths of light that chlorophylls cannot and provide other functions to the plant ex: xanthophylls, pheophytins, beta-carotene

A low polarity of many organic liquids means that

they do not mix (or not much) with water, not soluble if combined these liquids will form a bilayer with water

steps in performing column chromatography

to a pipette added wool, sand, silica gel (majority), and then another small layer of sand add hexanes to the spinach pigment residue that dried in the beaker the silica gel needs to be wetted, so add hexanes to the column, wetting with hexanes helps ensure a homogenous environment for the spinach pigments to travel through don't let the column ever go dry (refill needed) pipette spinach pigment solution into the column can flash the top of the column with small amount of air to speed up the progress rinse with hexanes add 90:10 hexanes: acetone (more polar than hexanes) -you'll see a yellow band form which is beta carotene, a very non polar pigment -collect the yellow pigment in separate vial add 70:30 mixture of hexane: acetone which is used to elute pigments more polar than beta carotene -blue-green band forms, collect these pigments in a vial -color will change slightly from blue-green to forest or olive green well collecting this pigment -collect the olive/forest green pigment in a separate vial

how many stereoisomers are possible when two chiral centers are present in the same molecule

up to four but if a stereoisomer has an internal plane of symmetry, its enantiomer does not exist (the mirror image is identical). this stereoisomer is a meso compound hydrobenzoin only has 3 stereoisomers: meso form and racemic mixture

column chromatography

vital to the characterization of molecules and can be used to purify molecules purification by chromatography requires preparation of a column of powdered silica (larger scale of chromatography than TLC) organic solvents (eluents) are run down through the column (a process called elution), usually by gravity a mixture of solutes can often be separated by passing it through a silica column, so that the solutes leave the column one at a time or in blends of just a few components to achieve effective separation, we must collect the liquid that exits the column in small aliquots called fractions one aspect of running a column that differs from thin layer chromatography is that we can change the liquid running through the column while the other solutes are traveling through it. this is called gradient elution -it enables us to recover the most mobile solutes early while other solutes stick to the column -changing the solvent composition then lets us push the stuck solutes through to be collected in later fractions the fractions collected from a column can be characterized by using TLC

the mobile phase

we almost never use a single solvent to elute solutes (move them along in chromatography) by blending solvents we can get an eluent (mobile phase) in all solvent blends there will be a nonpolar solvent (relatively) and a polar solvent When we change eluent polarity by using a different solvent blend, we change the balance of forces that cause a solute to stick or travel over the siica While the relative distance traveled by molecules (the order in which solutes appear on the plate) will not change with the polarity of the eluent, the overall all distance will be affected. In general, the more polar the eluent, the larger the distance each compound will travel

*know how to find R/S, look at note packet and problem set

when finding R/S make sure that the H is always dashed if the H isn't dashed but a wedge the stereochemistry switches from R to S or S to R (find R/S like normal by numbering priorities and then if it comes out to be R switch to S) If the H is a line look at packet for more detail... at the chiral go to each element directly bonded to that chiral carbon. at that element count all of the bonds off of that element and compare to the other elements of the chiral center to determine the priority -great atomic number= greater priority ex: C(C,C,H,O) is a greater priority than C(C,H,H,O)

racemic mixture

when we create a first chirality center (the intermediate, benzoin), both possible configurations (R and S) may be formed in equal amounts -we refer to this 50:50 mixture of enantiomers as a racemic mixture