Ochem Lab Final
The order of stability of alkyl carbocations is: _______ . In their reactions with ethanolic silver nitrate, different classes of alkyl halides follow an order of reactivity that reflects this factor. (SN1 experiment)
3° > 2° > 1° > methyl
This is an example of a heterogeneous distillation, specifically, a steam distillation. Under standard atmospheric pressure, a heterogeneous mixture of two volatile compounds will boil at the temperature at which the sum of the vapor pressures of the two pure compounds is _______. (DEHYDRATION OF CYCLOHEXANOL)
760 torr.
However, to insure that the temperature of the thermometer and of the sample are in equilibrium (i.e., efficient heat transfer) when the crucial measurement is being made, the rate of temperature rise when melting is actually occurring must not exceed _______ per min. (Determination of Melting Points)
2-3 °C
Better leaving group trend (SN1 experiment)
A better leaving group gets better as you go down the periodic table. Iodide is best LG > Br LG > Cl is worst LG (relatively speaking) Iodide ion is Weaker base > Bromide ion base > Cl is "stronger" base (relatively speaking)
erythro vs threo (both have chirality though) (Experiment 10: BROMINE ADDITION TO trans-CINNAMIC ACID)
Erythro has a much higher MP
These two non- superimposible stereoisomers are referred to as ____ (Experiment 6: Resolution of 1-Phenylethylamine)
enantiomers
Very precise melting points have been measured for a few compounds by determining the temperature at which the pure liquid and pure solid are in ______; a familiar example of this is the melting point of water, 0 °C. (Determination of Melting Points)
equilibrium
What if you can't read TLC? (TLC experiment)
expose the developed and dried plate to iodine vapor in a sealed vessel (e.g., a jar containing a few crystals of iodine). For many organic compounds, iodine will be reversibly and selectively adsorbed on the plate at points where the spots of organic material are located, producing readily visible brown spots Sometimes a fluorescent substance is incorporated in the stationary phase layer, and the positions of spots can be seen by examining the plate under ultraviolet light.
Sometimes mixtures of components whose solubility properties are too similar for separation by simple liquid-liquid extraction may still be separated: one component of the mixture must contain either an acidic or a basic functional group. In that case it may be possible to convert that component into a water-soluble salt by treatment with an aqueous solution of an inorganic base or inorganic acid as appropriate. The salt may then be separated from the other components of the mixture by ______ into the aqueous solution (Acid-base Extraction)
extraction
How does impurities affect MP? (Determination of Melting Points)
First, the melting point of the impure sample is usually depressed relative to that of the pure substance, and secondly, the melting point range is often off by a substantial amount. (depressed and broadening)
_________ is never used in a suction funnel, because creases in the paper would prevent it from seating properly in the Hirsch funnel or Buchner funnel. Instead, a circle of filter paper just large enough to completely cover the perforated or slotted disk in the bottom of the funnel is placed flat on top of the disk. (recrystallization)
Folded filter paper
Important note
For a fairly wide range of organic compounds, the detector response is relatively independent of the identities of the compounds, and is only dependent on the weights of the compounds present.
What type of distillation is used for this experiment (temp is high enough to distill of H2O and cyclohexene but not too high so cyclohexanol can't perform the E1 rxn) (DEHYDRATION OF CYCLOHEXANOL)
Fractional
____, also called alkyl halides, are very versatile organic compounds which are convenient starting materials for the synthesis of many other organic substances (SN1 experiment)
Haloalkanes
Error when heating too quickly? (Determination of Melting Points)
Heating too rapidly, the range will be much broader. Crystals melt quickly before the thermometer reaches the appropriate temperature level. So when doing rapid, the observed temperature would be lower than what is to be expected.
Important note (Acid-base Extraction)
When a carboxylic acid is present in a mixture with another organic compound, and if both compounds are relatively soluble in ether and insoluble in water, it will not be practical to separate them by extraction of their ether solution with water. However, if the other compound does not contain an acidic functional group (let's say it is "neutral" with regard to acid-base properties), it may be possible to separate the two compounds by extraction of their ether solution with dilute, aqueous NaOH. This converts the carboxylic acid into its sodium salt, which tends to be concentrated in the aqueous layer, while the neutral compound, whose properties are unchanged by treatment with aqueous NaOH, remains in the ether layer.
An even more effective method for promoting crystal formation is by "______" the cooling solution with a few crystals of the compound of interest, providing that some of the solid is available. (recrystallization)
seeding
In TLC the stationary phase is a finely divided _____ (typically silica gel or alumina AKA SLURRY), and the mobile phase is a _____. (TLC experiment)
solid; liquid
In TLC the ______ material is coated as a thin layer on an inert support such as a glass plate or sheet of plastic or aluminum. A sheet or strip of the support material which is coated in this way is called the "thin-layer chromatographic plate" or, simply, the TLC plate. (TLC experiment)
stationary phase
The column is a tube packed with the _____ material in finely divided form. Sometimes the ______ material in the column is simply a finely divided solid.
stationary phase
Permanganate ion reacts with an alkene at the carbon-carbon double bond. This process involves a _____ addition to the double bond to produce an unstable cyclic permanganate ester (PREPARATION OF SUBERIC ACID FROM CYCLOOCTENE)
syn
As the temperature of a liquid is increased, a point will be reached where the vapor pressure of the liquid will be equal to the external pressure over the liquid (in a routine distillation this is the pressure of the atmosphere). This temperature is the _______ of the liquid.
"boiling point"
______ material emerging at the end of the pathway,
"eluate"
What type of solvent do i choose? (recrystallization)
- must be chemically inert - large temperature dependence (high solubility in hot solvent) - impurities should either be insoluble in the hot solvent and removed during the hot filtration, or else sufficiently soluble in the cold solvent that they remain in the final filtrate after the purified crystals of the desired compound have been separated by suction filtration - solvent should be sufficiently volatile that residual traces will evaporate from the crystals that have been isolated within a reasonable amount of time. This is important since residual solvent will depress and broaden the melting point of incompletely dried crystals just as any other impurity would. 1 Chemically inert 2 Temperature dependent 3 Impurities should be insoluble at all temperatures 4 Volatile The pathway of assessing a good solvent: Dissolve at room temp (NO) Dissolves with heat (YES) Ice-water bath/crystals (YES)
The ee is usually reported as a percent and the ee of a racemic mixture is ___ while the ee of a single enantiomer is ___. (Experiment 6: Resolution of 1-Phenylethylamine)
0%; 100%
Bromine Test (DEHYDRATION OF CYCLOHEXANOL)
A positive test for an alkene or alkyne is the continued rapid disappearance of the red color with no significant evolution of HBr while several drops of the reagent are added. If there is reason to suspect that the unknown is a phenol or an amine the results should be interpreted with care. UNSATURATION colorless=double bonds.
Before vs After Shaking of extraction of carboxylic acid from ether using aqueous NaOH (Acid-base Extraction)
Before Shaking: - Ether (top): Neutral compound+ RCO2H - Water: NaOH After Shaking: - Ether (top): Neutral compound - Water: RCO2- Na+
______ such as plaster of Paris are sometimes incorporated with the silica gel or alumina to enhance the durability of the layer. (TLC experiment)
Binders
is defined as a method for the separation of a mixture into its components by distribution between a mobile phase and a stationary phase (TLC experiment)
Chromatography
Important note (Acid-base Extraction)
Congo red indicator is dark red above pH 4, changing color to very dark blue at lower pH.
In the case of a binary solution of two volatile compounds, both compounds contribute to the total vapor pressure of the solution, and the total vapor pressure may be expressed by ____ as the sum of the partial pressures of the two compounds:
Dalton's Law
Baeyer Test (DEHYDRATION OF CYCLOHEXANOL)
Dilute KMnO4 Alkenes and alkynes Purple solution turns to brown precipitate Positive test shows double bond
The mixture to be separated is applied to the ______ at the bottom end of the TLC plate (TLC experiment)
stationary phase
An important example of heterogeneous distillation called "_____" involves water as one of the two phases. Steam distillation is a very useful technique for purifying some organic compounds. It will be applied in some later experiments and discussed at that time. In this experiment, discussion is limited to homogeneous solutions.
steam distillation
_____ that is the two hydroxyl groups become attached to the same face of the double bond. (Experiment 10: BROMINE ADDITION TO trans-CINNAMIC ACID)
syn
For example, sometimes two or more compounds with different boiling points may form a solution that boils at a constant boiling point with constant composition. Such a solution is called an
azeotrope (ethanol and h2o)
Another way of defining the boiling point of a pure substance is that the boiling point is the temperature at which the pure liquid and its pure vapor are in ______
equilibrium
The upper layer is then carefully decanted out of the ______ of the separatory funnel, taking care to avoid contamination by droplets of the more dense layer that may have remained behind when the lower layer was removed. (Acid-base Extraction)
TOP
The relationship between vapor pressure and composition of a species in solution can be expressed in general by ________
Raoult's Law
Important note (TLC experiment)
The atmosphere inside the developing tank must be kept saturated with the vapor of the mobile phase in order to get reproducible results. Typically a "wick" of porous paper such as filter paper is used to partially line the inside of the tank and keep the atmosphere in the tank saturated with the mobile phase vapor. Only the very bottom edge of the plate, below the level of the spots is immersed in the liquid. The mobile phase rises up the plate through capillary action until the solvent front has moved an appropriate distance
Important note (recrystallization)
The hot solution after adjustment to the saturation point should not be cooled too rapidly.
Important note (Acid-base Extraction)
To isolate carboxylic acid, first heat the beaker containing the aqueous basic extracts with a steam bath for several minutes to drive off residual traces of dissolved ether. Cool the beaker in an ice bath and make the solution distinctly acidic to Congo red indicator paper (Note 5) by rapid drop-wise addition of 6M hydrochloric acid to the stirred solution. Cool the resulting mixture thoroughly in an ice bath for 10-15 min to insure that precipitation is complete. Collect the solid by suction filtration, wash it under suction with a few mL of ice cold water, press the solid dry under suction, then dry on a watch glass.
The mobile phase solvent is allowed to move up TLC plate by _____, carrying the components of the mixture with it. (TLC experiment)
capillarity
(two liquids are _____ if they are completely soluble in each other, giving a homogeneous solution) (recrystallization)
miscible
Neutralization of the aqueous solution is then performed to convert the salt back to the original non-ionic form. This variation of liquid-liquid extraction is referred to as ______ extraction. (Acid-base Extraction)
"acid-base"
A ____________ provides a much more efficient means of separating solutions containing two or more volatile components with different boiling points.
"fractional distillation"
Mixtures of volatile components can often be analyzed conveniently by an instrumental technique known as ______
"gas chromatography."
Typical drying agents are various anhydrous salts that have the ability to combine with water to form solid ________ Some common salts used as drying agents are calcium chloride, sodium sulfate, magnesium sulfate, barium oxide, and potassium carbonate. Drying agent must be inert. (Acid-base Extraction)
"hydrate complexes."
What apparatus do I use for liquid-liquid extraction? (Acid-base Extraction)
"separatory funnel", which is designed to permit the convenient and efficient mixing and subsequent separation of two immiscible liquid layers
The ________ of a liquid is a measure of the number of molecules that are escaping into the gas phase.
"vapor pressure"
A narrow or "sharp" melting point range ______ is generally considered as circumstantial evidence that the compound is pure. (Determination of Melting Points)
(0.5 to 2.0 °C)
Important note (Experiment 6: Resolution of 1-Phenylethylamine)
(R)-1-Phenylethylamine (depicted above) cannot be superimposed with its mirror image. When a racemic mixture (a 1:1 ratio of enantiomers) of 1-phenylethylamine is reacted with a single enantiomer of tartaric acid, two diastereomeric salts form (in a 1:1 ratio). These complexes are not mirror images of one another since only a single enantiomer of tartaric acid is used in the reaction. Thus, (R)-amine, (R, R)-tartaric acid salt and (S)- amine, (R, R)-tartaric acid salt are formed.
The _______:(R, R)-tartaric acid salt is more soluble in methanol than the (S)-amine:(R, R)-tartaric acid salt (Experiment 6: Resolution of 1-Phenylethylamine)
(R)-amine
Why do you want a chamber in TLC? (TLC experiment)
. More surface area means more and faster evaporation. More evaporation means more solvent vapor in the chamber's air, which is desirable. You want your chamber air thoroughly impregnated with solvent vapor in TLC because this keeps the stationary phase from drying out before the process is finished. The solvent evaporating from the paper saturates the chamber's air so it doesn't wick solvent off the stationary phase as quickly. If the stationary phase dries out prematurely, the components in the sample won't separate properly and your results will be incorrect. The stationary medium should remain dampened with solvent until you remove it from the chamber and dry it on purpose.
The efficiency of separation achieved in a fractional distillation depends on a number of factors:
1) Surface area of the packing material in the column: the heat transfer between the liquid and vapor phases in the column is more efficient when there is a large surface area. 2) Length of the distilling column: the longer the column, the greater the number of condensation-vaporization cycles there will be as material moves up the column. 3) Difference in the boiling points of the components being separated: the greater the difference, the more easily the components may be separated. 4) The rate of heating: if heating is too rapid, the quantity of vapor produced may exceed the capacity of the column to effect equilibration, and separation efficiency will suffer. On the other hand, if too little heat is supplied, the rate of distillation will be too slow to be practical.
Recrystallization steps (recrystallization)
1) The sample is dissolved with heating in a solvent which is suitable for effecting the desired purification. 2) The hot solution is filtered under gravity to remove any insoluble impurities. 3) The hot solution is concentrated or is treated with a co-solvent to give a hot solution which is near the saturation point for the compound being purified. 4) The hot solution is allowed to cool to room temperature, and then it is cooled in an ice bath until crystallization of the desired compound is as complete as possible. 5) The solid is collected by suction filtration, washed with a small amount of cold solvent, and dried.
What tests do you use to determine if alkenes or alkynes are present? (DEHYDRATION OF CYCLOHEXANOL)
Bromine and Baeyer test
A distillation must NEVER be attempted in a ____system, since the pressure which would develop upon heating would eventually lead to an explosion. The same may be said for any other laboratory operation; never heat a closed system!!!
CLOSED
______ are normally resistant to further oxidation under the conditions of permanganate cleavage of an alkene. (PREPARATION OF SUBERIC ACID FROM CYCLOOCTENE)
Ketones
How do i separate the ether component of an acid-base extraction? (Assume both components are insoluble in water but soluble in ether) (Acid-base Extraction)
One component of the mixture will contain a functional group that is acidic, which will allow it to be converted into a water soluble salt when the mixture is treated with aqueous sodium hydroxide. Extraction of an ether solution of the mixture with dilute, aqueous sodium hydroxide, then, effects the separation of the two components, with one remaining in the ether layer and the other going into the aqueous layer in the form of a salt. Evaporation of the ether solution allows you to recover one of the compounds
What if you have 2 sample spots on TLC plate? (TLC experiment)
One records the data from the chromatogram in terms of the ratios of the distances traveled by each component compared to the distance traveled by the solvent... likely a mixture.
How can efficiency of separation be measured? (Acid-base Extraction)
Partition/distribution coefficient K=(Concentration of Y in solvent 1)/(Concentration of Y in Solvent 2). or K = (grams of Y/mL of Solvent 1)/(grams of Y/mL of Solvent 2) Best answer for K is either 0 or infinity.
After shaking, you can acidify with a strong solution which converts the sodium carboxylate salt back to the free carboxylic acid (Acid-base Extraction)
RCO2-Na+ + HCl -> RCO2H + NaCl
In step b, a molecule of water is lost, producing a carbocation, in which there is a carbon atom which has an incomplete octet of valence electrons and a positive charge. This step occurs very slowly. This step is the _____ in the reaction (Sn1 experiment)
RDS
Polarimeter schematic (Experiment 6: Resolution of 1-Phenylethylamine)
Regular light -> Polarizer -> Plane-polarized light->Sample cell with optically active material-> rotated plane-polarized light->detector
Important note (recrystallization)
Single solvent system - saturation point achieved via boiling off some of the solvent Mixed solvent system - saturation point adjusted via addition of a solvent in which the compound is less soluble
What is the acid's function (DEHYDRATION OF CYCLOHEXANOL)
The acid is a catalyst, and it catalyzes the dehydration by lowering the energy required to cleave the carbon-oxygen bond
What is so special about fractional distillation?
The principal difference between this apparatus and the simple distillation apparatus of Figure 1 is the distilling column, sometimes referred to as a "fractionating column" located between the pot and the distillation head in the apparatus. Distilling columns vary greatly in design and efficiency, but their basic function is to serve as a rather inefficient condenser. The distilling column in Fig. 4 is constructed with a jacket that makes it less susceptible to drafts, but although it looks similar in design to the condenser, it is not cooled with water. The inside of the distilling column is packed with some sort of inert material such as glass beads or rings, steel wool, or other material which provides a large surface area within the column
eluant (TLC experiment)
The solution used to wash material through a chromatographic column.
What are boiling chips
These porous, inert chips help maintain smooth boiling as their rough surfaces and tiny trapped pockets of air promote bubble formation and prevent superheating and the resulting bumping.
Organic salts (Acid-base Extraction)
These salts tend to be much more soluble in aqueous solution and much less soluble in solvents of low polarity such as ether than the free organic substance from which they were formed
specific rotation (Experiment 6: Resolution of 1-Phenylethylamine)
a = observed rotation / concentration * length
Common strategies for maximizing the yield of a particular product in an equilibrium reaction are either to use ______________ (DEHYDRATION OF CYCLOHEXANOL)
a large excess of one of the reactants, or to remove one of the products as rapidly as it is formed (latter is used in this experiment because BP of alkene is lower than BP of alcohol).
supersaturation (recrystallization)
a state of a solution that contains more of the dissolved material than could be dissolved by the solvent under normal circumstances
Dibromination (Experiment 10: BROMINE ADDITION TO trans-CINNAMIC ACID)
electrophilic addition across an alkene (stereospecific)
Some organic solvents are unsuitable for use in the extraction of aqueous solutions because they are miscible with water. Some solvents of this type are _____________If one of these solvents is added to water, no separation of layers occurs, the solvent and water form a homogeneous solution. (Acid-base Extraction)
acetone, ethanol, methanol, acetic acid, or pyridine.
The function of the ____ is to facilitate the dissociation of the carbon-oxygen bond. If the _____ were not present, then formation of the carbocation would require an ionic dissociation to produce a carbocation and a hydroxide ion (DEHYDRATION OF CYCLOHEXANOL)
acid
Some types of impurities may be removed during recrystallization by adding a small amount of ________ to the hot solution before filtering off the insoluble impurities. Activated carbon is also sometimes called activated charcoal, decolorizing carbon, or Norite. It does not dissolve in the solution, but the surface of the carbon is highly adsorbent, and some types of polar, tarry contaminants strongly adhere to the carbon particles (recrystallization)
activated carbon
TLC is most commonly used as a very sensitive _____ technique, capable of analyzing samples at the microgram level. However, if plates of larger size are used, and if the coating of stationary phase material is thicker, it may be possible to separate quantities on a small preparative scale, up to 100 mg or more (TLC experiment)
analytical
Whenever bromine is being used it is a wise precaution to have a "safety solution" of ________ standing by. In case of spills the affected area should be flooded with this safety solution and then washed with water. In case of skin contact, after washing with safety solution and water, rubbing ______on the affected area helps to minimize damage. Dichloromethane is moderately toxic and has been shown to be carcinogenic upon prolonged exposure in high concentrations. (Experiment 10: BROMINE ADDITION TO trans-CINNAMIC ACID)
aqueous sodium thiosulfate; glycerin Note: you can cry because of this lab
Unlike the electrons in SIGMA-bonding orbitals, which spend most of the time located in the region that is _____ the atoms involved, the electrons in the PI-orbital of an alkene occupy a pair of lobes above and below the plane of the atoms of the system, where they are exposed to attacking reagents. Furthermore, the -bond component of the double bond is relatively weak and more polarizable compared to the carbon-carbon -bonds of alkanes. As a result, the carbon-carbon double bond undergoes reactions with a variety of reagents. (PREPARATION OF SUBERIC ACID FROM CYCLOOCTENE)
between
When an alkene reacts with permanganate without cooling and under basic conditions, cleavage of the ______ occurs (PREPARATION OF SUBERIC ACID FROM CYCLOOCTENE)
carbon-carbon double bond
The principal site of reactivity in alkenes is the ______ (PREPARATION OF SUBERIC ACID FROM CYCLOOCTENE)
carbon-carbon double bond.
organic compounds containing the _____functional group are converted by aqueous NaOH into sodium carboxylate salts, regardless of the nature of the specific "R" group that is present. (Acid-base Extraction)
carboxyl
If an aldehyde is produced as a product of permanganate cleavage of the alkene, the aldehyde is oxidized further by permanganate under basic conditions to give a ______. (PREPARATION OF SUBERIC ACID FROM CYCLOOCTENE)
carboxylate salt
An object that has a non-superimposable mirror image is referred to as being ______ (Experiment 6: Resolution of 1-Phenylethylamine)
chiral
For a given enantiomer the degree of rotation α is dependent on the ______________. Typically, the yellow light of a sodium lamp (the "D" line of Na, wavelength = 589 nm) is used as a light source (Experiment 6: Resolution of 1-Phenylethylamine)
concentration of the compound (c), the path length of the sample cell (l), and the wavelength of light that is used.
The enantiomeric excess (ee) of a compound can be calculated using the equation below: (Experiment 6: Resolution of 1-Phenylethylamine)
ee = % of the major enantiomer - % of the minor enantiomer.
Once the sample has been introduced onto the plate, the chromatogram is _____ by placing it upright in a developing chamber that contains some of the mobile phase liquid a few millimeters in depth. (TLC experiment)
developed
The ______ of the red color of bromine as it is consumed by reaction with the carbon-carbon double bond is considered circumstantial evidence for the presence of the alkene functional group. (Experiment 10: BROMINE ADDITION TO trans-CINNAMIC ACID)
dissapearance
If the distillation has been successful, the "______", that is, the liquid that is collected as the vapor condenses, will be in a higher state of purity than the original sample before distillation.
distillate
The separation and purification of volatile liquids is frequently accomplished by applying a technique known as ______. an impure liquid vaporized by heating, and the vapor is separated from less volatile material, collected, and cooled.
distillation
If a compound of interest is much more volatile then the contaminants present, separation is easy, and a very straightforward "simple distillation" may suffice. In the case of mixtures containing more than one volatile component the separation provides a greater challenge and may require the application of a more sophisticated apparatus in a technique known as "___________."
fractional distillation
A __________ is a particular arrangement of atoms within a molecule that can be expected to exhibit a characteristic pattern of reactivity, regardless of the structure of the rest of the molecule ( Experiment 10: BROMINE ADDITION TO trans-CINNAMIC ACID)
functional group
It was noted above that the vapor pressure of a liquid is a measure of the number of molecules that are escaping into the ____ phase
gas
When choosing a mixed solvent combination, the two solvents chosen for the combination should be a pair of solvents with a ________ in each other and with reasonably different polarity properties. (recrystallization)
high mutual solubility
The melting point of a pure crystalline solid is usually sharp and _______ (recrystallization)
highly reproducible
Never add ________ solutions to the separatory funnel. This is especially important when very volatile solvents are being used, since dangerously high vapor pressures may develop in the closed funnel during mixing (Acid-base Extraction)
hot
vapor pressures and the relative strengths of their attraction to the stationary phase material. When a component reaches the end of the column it is carried through a detector chamber where its presence causes an electrical response that is conveyed to a recorder, which produces the gas chromatogram (GC trace).
important note
the composition of the vapor is always richer in the more volatile compound than the liquid with which it is in equilibrium.
important note whatever this means
"lipophilic," because its solubility behavior resembles that of biological substances of low polarity known as "_____." _____ are biological substances that are soluble in solvents of low polarity, and include such biomolecules as fats, steroids, terpenes, etc. (PREPARATION OF SUBERIC ACID FROM CYCLOOCTENE)
lipids
filtrate (recrystallization)
liquid phase from which the solid has been removed by filtration
When plane-polarized light is passed through a single enantiomer of a chiral molecule (more commonly a solution of a single enantiomer of a chiral molecule), the plane of polarization is ______. (Experiment 6: Resolution of 1-Phenylethylamine)
rotated
Two liquids are said to be "miscible" if they are completely soluble in each other, while two "immiscible" liquids have only limited solubility in each other and exist as separate phases when the quantities used exceed those solubility limits. The general term used to describe the partitioning process is "_______" extraction. (Acid-base Extraction)
liquid-liquid
The _____ point of a solid compound is the temperature at which a phase transition from solid to liquid occurs.For pure crystalline compounds the melting point is commonly sharply defined and highly reproducible, and it represents the temperature at which thermal energy is sufficient to break down the crystal lattice of the solid. (Determination of Melting Points)
melting
Some common mixed solvents are such _____ pairs as acetone-water, ethanol-water, ether-petroleum ether, benzene-hexane, chloroform-hexane, or ethanol-ether (recrystallization)
miscible
In gas chromatography the _____ phase is a stream of gas (in this case helium), which moves through the "GC column"
mobile
During the development, the end of the plate below the initial spotting points will be immersed in a shallow pool of the _____ material, and it is important to position the spots high enough on the TLC plate so that they will not be below the surface of the mobile phase (TLC experiment)
mobile phase
Chromatography is a term that encompasses a number of separation techniques that involve the partitioning of the components of a mixture between a ______________-
mobile phase and a stationary phase.
The acid catalyst, is phosphoric acid, which has an even higher boiling point, and it remains behind in the reaction vessel as the product distills off. Therefore, the distillate contains no acid which might catalyze the reverse reaction. The choice of phosphoric acid, rather than other common acids is based on the fact that the phosphate counter ion is ___________ (DEHYDRATION OF CYCLOHEXANOL)
nonnucleophilic, which minimizes substitution pathways.
DEFINE : when the compound of interest separates from the solution too rapidly upon cooling to permit the molecules to arrange themselves in an orderly crystalline array. As a result the material may begin to separate as a viscous liquid or oil, which can trap significant amounts of impurities. Usually this oil does eventually solidify on further cooling, but it is apt to appear as large clumps with a broad melting point range, rather than the sharp-melting crystals that are desired. _______ is most frequently a problem for fairly low-melting solids, especially those whose melting points are lower than the boiling point of the solvent being used. In those cases the usual procedure is to warm the solution again until the oil redissolves, add a bit more solvent, and cool again, even more gradually than before. (recrystallization)
oiling out.
By comparing the specific rotation of a sample prepared in the laboratory with the published specific rotation of an enantiomerically pure sample, one can calculate the _____ of the sample. If the relationship between concentration and rotation is linear, then optical purity = ee(%). (Experiment 6: Resolution of 1-Phenylethylamine)
optical purity
. Samples that rotate polarized light are said to be ______. The magnitude of this rotation, α, is reported in degrees by a device called a polarimeter (Experiment 6: Resolution of 1-Phenylethylamine)
optically active.
A racemic mixture will not rotate polarized light and is said to be ______ (Experiment 6: Resolution of 1-Phenylethylamine)
optically inactive
Concentration is continued until clouding or the onset of crystal formation indicates that you have passed the _______, then a small additional amount of solvent is added until the hot solution is once again homogeneous (recrystallization)
saturation point
One of these methods involves _____ of the alkene, which, after reductive work up of an intermediate ozonide, gives aldehydes and ketones as the usual products. The other method that is widely used is the reaction of the alkene with potassium permanganate. Under appropriate conditions, the double bond is cleaved by permanganate to give ketones and/or carboxylic acids. (PREPARATION OF SUBERIC ACID FROM CYCLOOCTENE)
ozonolysis
Mixtures containing components with very different solubility properties may often be separated by the distribution, or "______" of the components between two "immiscible" liquid phases. (Acid-base Extraction)
partitioning
______ and ligroin are solvents consisting of mixtures of saturated hydrocarbons isolated as distillate fractions from petroleum. Different distillate fractions are typically designated by their boiling point ranges, such as 30-60, 60-90, or 90-120 °C. The solvent properties of ____ or ligroin are similar to those of pure saturated hydrocarbons such as hexane, heptane, cyclohexane, etc., but they are less expensive (petroleum ether is volatile) (recrystallization)
petroleum ether
Achiral molecules also do not rotate ___________ (Experiment 6: Resolution of 1-Phenylethylamine)
plane-polarized light
A _____ will be used to determine the optical rotation of the product, from which we can determine enantiomeric excess and evaluate the efficiency of our resolution. (Experiment 6: Resolution of 1-Phenylethylamine)
polarimeter
Any excess of one enantiomer over the other will result in the rotation of _______, with the maximum rotation occurring when the sample consists of a single enantiomer (Experiment 6: Resolution of 1-Phenylethylamine)
polarized light
In the case of methanol or a ______, carbocation formation is energetically less favorable. Therefore, methanol or primary alcohols commonly undergo reaction by the SN2 mechanism (SN1 experiment)
primary alcohol
An equimolar mixture of two enantiomers is known as a _____ (Experiment 6: Resolution of 1-Phenylethylamine)
racemic mixture (or racemate).
The boiling point of a liquid may be lowered by ____ the pressure over the system
reducing
The _________ of a component is defined as the time required for the compound to travel through the column from the injection port to the detector and is measured at the midpoint of the peak.
retention time
In order for the permanganate ion to react with cyclooctene it is first necessary to bring them together in the same phase. In order to achieve this you will use a substance known as Aliquat 336, which functions as a phase-transfer catalyst. Aliquat 336 is a trade name for __________. quaternary ammonium salts spectator (PREPARATION OF SUBERIC ACID FROM CYCLOOCTENE)
trioctylmethylammonium chloride.
Distillation carried out in a system under reduced pressure is called "____." Of course, the precise boiling point of a substance will vary with altitude and changes in barometric pressure; however, within normal pressure ranges, the effect is small enough that it need not be considered in routine situations
vacuum distillation
In dissociation processes leading to carbocation intermediates, the best "leaving groups" are _______; in this case we say that protonation of the alcohol converts a poor leaving group (the hydroxide ion) into a much better leaving group (a water molecule). (DEHYDRATION OF CYCLOHEXANOL)
very weak bases
In the cold, using dilute aqueous solutions of potassium permanganate at neutral pH, the ester undergoes hydrolysis to give a ____ diol (a diol is an alcohol having two hydroxyl groups; two groups are "vicinal" if they are located on adjacent carbons) (PREPARATION OF SUBERIC ACID FROM CYCLOOCTENE)
vicinal
Two groups are said to have a _____ relationship when they are located on adjacent carbon atoms in an organic molecule. (Experiment 10: BROMINE ADDITION TO trans-CINNAMIC ACID)
vicinal
Spotting the sample is done by preparing a solution of the sample in a convenient _____ solvent (acetone, dichloromethane are common) and then transferring a few microliters of this solution to the plate. (TLC experiment)
volatile
The washing process should be recognized as simply an extraction, except that in those cases you are usually only interested in saving one of the layers, while the "_____" layer contains only impurities, and is discarded (Acid-base Extraction)
wash
In the following experiment the alcohol, cyclohexanol, will be converted into an alkene by elimination of ______. The change in functionality from the alcohol to the alkene can be detected by performing examining its reactivity with _________. (DEHYDRATION OF CYCLOHEXANOL)
water; molecular bromine
How do i separate the acid component of an acid-base reaction? (Acid-base Extraction)
will be isolated from the aqueous solution after extraction by acidification to convert the salt back into the free organic acid, which is insoluble in water, and which can be isolated by suction filtration.