orgo 2 Flashcards
What is the IR absorbance for carbonyl?
1700cm^-1
sharp deep
What is the IR absorbance for alcohol ?
3300cm^-1
broad separate from CH
What is the IR absorbance for saturated alkane CH?
2800 cm^-1
sharp deep
What is the IR absorbance of carboxylic acid OH?
3000 cm^-1
broad overlap CH
What is the IR absorbance for amine NH?
3300cm^-1
broad shallow
What is the IR absorbance for amide NH
3300cm^-1
broad deep
what is the IR absorbance for nitriles, C=N ?
2250 cm^-1
sharp deep
What does IR absorbance represent?
only represent a single polar bond within a molecule.
If there’s no dipole = no absorbance
Who does UV light spectroscopy work?
When a molecule is exposed to UV radiation, electrons within that molecule will often absorb that energy and excite to the next highest energy level. ABSORBANCE is recorded on UV spectrum.
Which molecules show no or low UV absorbance?
molecules that contain ONLY single bonds.
Which bonds absorb molecules strongly?
double and triple bonds
What molecules absorb even more UV than do isolated double or triple bonds?
conjugated systems.
The greater the degree of conjugation, the farther to the right the species will absorb.
What is mass spectroscopy ?
the molecules of the sample are bombarded with electrons causing them to both break apart into smaller pieces and ionize, so you get fragments with different masses and charges. Only particles with a certain mass to charge ration (m/z) will follow the exact curved path necessary to NOT hit he walls and exit onto the detector at the end of the flight tube.
On a mass spectroscopy, what does the parent peak represent? what does the base peak represent?
parent peak: represents the original molecule minus one electron (aka molecule ion peak)
base peak: most common fragment and is usually the most stable fragment generated = highest fragment generated
Q5. If the velocity of particles in the flight tube of a mass spectrometer is held constant while the strength of the magnetic field is increased linearly, how will the mass of particles striking the detector vary with time?
A linear increase in the magnetic field will create a linear increase in the force exerted on the particles according to: F = qvBsin. For a curved flight tube with a detector at the far end, in order for any particle to strike the detector it must experience exactly the right centripetal acceleration to trace the precise curvature that results in striking the detector. As the centripetal force increases this will occur for increasingly massive particles. The graph below shows the linear relationship between magnitude of the B field and mass of particles at the detector.
What is NMR?
Differentiate molecules based on hydrogen
What must an atom have in order to register on an NMR?
odd atomic number or odd mass number.
How does the MCAT think of MRI’s?
HNMR for the human body
Nuclear spin causes small changes in the electric field and—as you should remember from physics—a changing electric field creates a ____?
magnetic field
How do IR help us identify molecule?
based on function groups
What do the peaks represent in a H-NMR?
peaks represent all the hydrogens in a molecule that share an indistinguishable chemical environment.
What does the area under the H-NMR peak represent?
the number of hydrogens accounted for by the peak
What is the absorbance range? what does it represent?
0 -12 ppm.
12ppm= downfield= deshielded
0 ppm= upfield = shielded
What is the absorbance range of a C13-NMR spectrum?
0 -220ppm
220 ppm: downfield= desuhielded
0 ppm= upfield = shielded
What is the C13 NMR absorbance for C-C ?
0-50
What is the C13 NMR absorbance for C-O ?
50-100
What is the C13 NMR absorbance for C=C ?
100- 150
What is the C13 NMR absorbance for C=O ?
150- 200
1) The synthesis of the drug Prostratin from naturally occurring Phorbol is shown. The product is a mixture of Prostratin and unreacted Phorbol. Spectroscopic analysis is used to determine percent yield. An H-NMR spectrum for Prostratin would differ from an H-NMR spectrum for Phorbol in that the H- NMR for Prostratin would include:
A) one additional proton signal
B) two additional proton signals
C) one additional proton signal, one additional ester signal and two fewer alcohol signals
D) one less proton signal
D
what is the purpose of extraction?
to separate wo compounds based on solubility (polar and non polar layer)
In an extraction, is the polar solvent in the bottom or top layer?
non polar layer is less dense and often on top; polar layer is most often on bottom.
What are three things to avoid while separating?
1- mixing too vigorously
2- reactive solvents
3- high boiling point
what is fractional extraction?
extracting small amount multiple times rater than one big amount to reduce impurity.
What is gravity filtration?
physical separation of a solid from a liquid by passing it through filtration paper. Fluted filter paper is recommended.
what is vacuum filtatrion?
Vacuum filtration is performed with a Hirsch or Buchner funnel. A vacuum is created inside of the flask which creates suction to pull the filtrate through the filter paper. The filter usually has holes in it which are covered by the filter paper. The primary advantage is that it is faster than gravity filtration.
What is distillation used for?
separate two substances by simple distillation they must have boiling
2) A lab procedure instructs students to obtain an amine product by first acidifying the ether solution and then extracting multiple times with an aqueous solvent. If a student uses 1.5 M hydrochloric acid instead of the 2.5 M hydrochloric acid he is instructed to use by the lab manual, which of the following will result?
A) More ether molecules will be protonated and move into the aqueous layer, thus producing a better yield.
B) Fewer amine molecules will be protonated and move into the non-polar layer, thus producing a lower yield.
C) Fewer aqueous water molecules will form hydronium ions, decreasing the pH of the solution and thus producing a better yield.
D) Fewer amine molecules will be protonated and move into the aqueous layer, thus producing a lower yield.
Using a lower molarity acid will decrease the ability of the acid to protonate the amine and bring it into the aqueous layer (the desired effect). This will decrease yield. Answers A and C are eliminated because they predict an increased yield. Answer B is incorrect because charged amine molecules will be more soluble in the aqueous layer than in the non-polar layer. Answer D is thus correct.
What is chromatography?
What is the first substance to elute?
separating one or more compounds by dissolving them in a mobile phase and then passing that phase through or across a stationary phase based on their polarity.
the more polar substance will stick to the stationary phase longer and the LEAST polar substance with be the first substance out of the tube.
what is paper or thin layer chromatography TLC ?
uses paper as stationary phase. TLC uses glass or plastic sheets coated with silica alumina, etc
what is rf?
Rf = distance traveled by component /distance traveled by solvent
If Rf = 0.9, is the substance in question polar or non-polar?
Given that Rf is a ratio of the distance traveled by the component over the distance traveled by the solvent. So a number close to one means that the polarity of the component is similar to that of the solvent. Because non-polar solvents are normally used, the component is therefore relatively non-polar.
During TLC, or paper chromatography, components will sometimes form an upward “smear” instead of forming a cohesive dot. Provide some possible causes of smearing.
Smears are usually caused when the solvent is unable to dissolve and carry the components as it moves up the paper via capillary action. This can be because too much of the sample was spotted onto the paper and the solvent could not dissolve the entire sample. It can also occur if there is too big of a difference in polarity between the sample and the solvent. If the polarities are too distant the solvent cannot dissolve the sample well enough to carry it. By a similar token, if they are too similar, the components may never come out of solution to form a spot and be carried all the way to the top of the paper.
What is column chromatography?
The mixture to be separated is passed through a column packed with charged glass beads, or some other polar matrix. The solution is collected in fractions at the bottom of the column (i.e., the collecting tubes are changed at regular intervals).
Which compounds will be eluted at the bottom of the column first?
In column chromatography, assuming a polar matrix, the most non-polar substances will elute first, followed by increasingly more polar substances.
What is ion exchange chromatography ?
The column or stationary phase is coated with cations or anions. The mixture is passed through and oppositely-charged ions adhere to the column. The target molecules can then be eluted by washing with a salt solution.
What is affinity chromatography?
Used to isolate a specific molecule or product based on a very specific affinity or binding interaction. For example, it may be that molecules in the mixture react via acid-base neutralization with molecules on the column. To elute the bound target molecules one must disrupt the binding interaction. This could be accomplished via a salt solution, but often requires a chemical reversal of the reaction that bound the target to the column.
What is gas chromatography?
A liquid is used as the stationary phase. The mixture is dissolved into a heated gas and then passed through the liquid. Various components reach the exit port at different rates based on 1) boiling point and 2) polarity. Only consider polarity if the two substances have almost identical boiling points.
–> there will be one peak for each unique compound in the mixture.
What causes one peak to be higher than another on a gas chromatograph?
The HEIGHT of the peak in a gas chromatograph is relative to the abundance of that component.
A student tests the melting point of his crystals to determine purity. Does a higher melting point indicate more purity or less?
Higher and sharper melting points indicate better purity. Impurities lower melting point. They also broaden the range across which the crystals melt.
Who does the double bond of a carbonyl (C=0) differ from the alkene double bond?
shorter and stronger because oxygen has greater electronegativity + Compared to two carbons, a carbon and an oxygen can get closer to one another because oxygen has a smaller atomic radius. This allows for more pi overlap and therefore a stronger bond.
