Chapter 11: Spectroscopy and Chapter 12: Separations and Purifications Flashcards
What does spectroscopy measure?
The energy differences between the possible states of a molecular system
How does spectroscopy work?
Determining the frequencies of EM radiation absorbed by the molecules
What does infrared (IR) spectroscopy measure?
Molecular vibrations
How is an IR spectrum recorded?
IR light is passed through a sample, and the absorbance is measured
By determining what bonds exist within a molecule, we hope to infer what?
The functional groups in the molecule
The useful absorptions for spectroscopy occur at wavelengths of what?
2500 to 25,000 nm
On an IR spectrum, we use an analog of frequency called ____________.
wavenumber
When light of these wavenumbers is absorbed, what happens to the molecules?
They enter excited vibrational states.
What are 4 types of vibration that can occur?
- symmetric bend
- asymmetric bend
- symmetric stretch
- asymmetric stretch
More complex vibration patterns, caused by the motion of the molecule as a whole, can be seen in what wavenumber range? This is called the ________________ ________ because the specific absorbance pattern is characteristic of each individual molecule.
1500 to 400 cm-1 range; the fingerprint region
For an absorption to be recorded, the vibration must result in a change in the ____________ ____________ ____________.
bond dipole moment
Which molecules do not have recordable absorptions?
Molecules that do not experience a change in dipole moment, such as those composed of atoms with the same electronegativity or molecules that are symmetrical
The hydroxyl group absorbs with a ________ peak at around one of two frequencies: ________ cm-1 for alcohols, and ________ cm-1 for carboxylic acids.
broad; 3300, 3000
The carbonyl of a carboxylic acid pulls some of the electron density out of the OH bond, shifting the absorption to a ____________ wavenumber.
lower
The carbonyl absorbs around ________ cm-1 with a ________ peak.
1700; sharp
The bond between any atom and hydrogen always has a relatively ________ absorption frequency. As we add more bonds between carbon atoms, the absorption frequency ____________.
high; increases
N-H bonds are in the same region as O-H bonds at ________ cm-1 but have a ________ peak instead of a ________ one.
3300; sharp instead of broad
IR spectra are plotted as percent ________________, the amount of light that passes through the sample and reaches the detector, vs. wavenumber.
transmittance
UV spectra are obtained by passing ________ light through a sample that is usually dissolved in an inert, nonabsorbing solvent, and recording the ____________.
absorbance
UV spectra plot what?
absorbance against wavelength
The most significant piece of info we get from UV spectroscopy is the ____________ of ____________ ____________, which tells us what?
wavelength of maximum absorbance; the extent of conjugation within conjugated systems
The more conjugated a compound is, the ________ the energy of the transition and the ________ the wavelength of maximum absorbance.
lower; greater
Molecules with a lower energy gap between ________ occupied molecular orbital and ________ unoccupied molecular orbital are more easily ________ and can absorb ________ wavelengths (lower frequencies) with lower energy.
highest; lowest; excited; longer
high yield
UV spectroscopy is most useful for studying compounds containing ________ bonds or heteroatoms with ________ ________ that create conjugated systems.
double; lone pairs
____________ molecules, or molecules with ____________ p-orbitals, can also be excited by UV light.
conjugated; unhybridized
Conjugation shifts the absorption spectrum, resulting in ________ maximum wavelengths.
higher
Nuclear magnetic resonance (NMR) spectroscopy is based on the fact that certain atomic nuclei have ____________ ____________ that are oriented at random.
magnetic moments
When certain atomic nuclei are placed in a magnetic field, their magnetic moments tend to align either with or against the direction of this applied field.
Nuclei with magnetic moments that are aligned with the field are said to be in the ____-state (lower energy).
alpha
Nuclei in the alpha state can be irradiated with radiofrequency pulses that match the energy gap between the two states, which will excite some lower-energy nuclei into the ____-state (high energy).
beta
What does NMR plot?
frequency vs. absorption of energy
NMR uses an arbitrary variable called ____________ ________ with units of parts per million of spectrometer frequency.
chemical shift
The chemical shift is plotted on the x-axis, and it ________ toward the left (referred to as ________.
increases; downfield
To make sure that we know just how far downfield compounds are, we use ________ as the calibration standard to mark 0 ppm; when counting peaks, make sure to skip its peak.
TMS
NMR is most commonly used to study what?
1H nuclei (protons)
Any atom with a ________ ________ (an odd atomic number, odd mass number, or both) can be studied with NMR.
nuclear spin
MCAT only tests 1H NMR
Most hydrogen (1H) nuclei come into resonance ____ to ____ ppm downfield from TMS.
0 to 10
Each distinct set of nuclei gives rise to a ____________ peak.
separate
This means that if multiple protons are ____________ ____________, having the same magnetic environment, they will lead to the same peak.
chemically equivalent
The height of each NMR peak is proportional to what?
The number of protons it contains
The ratio of the protons correponds to the ratio of protons produced at each peak
Each peak or group of peaks that are part of a multiplet represents what?
A single group of equivalent protons
The relative area of each peak reflects what?
The ratio of protons producing each peak
The position of an NMR peak is due to what?
Shielding and deshielding effects
If near electronegative atoms, electron density will be pulled away from protons, and the less it can shield itself from the applied magnetic field. What does this result in?
A reading further downfield
If we had an EDG, it would shield the nuclei and give it a position further ________.
upfield
Everything in proton NMR will be more ____________ than TMS, thus it will be ____________.
deshieleded; downfield
When we have 2 protons in close proximity that are not magnetically identical, ____-____ ____________ (____________) occurs.
spin-spin coupling (splitting
(hydrogens on two adjacent atoms – within 3 bonds of each other)
If there are 2 protons in close proximity, one proton will be in either one of two energy states (alpha or beta). Thus the resulting absorption is a ____________: 2 peaks of identical intensity, equally spaced around the true chemical shift of the other proton.
doublet
TO determine the number of peaks present, we use the ________ rule.
n + 1
What does the n+1 rule state?
If a proton has n protons that are 3 bonds away, it will be split into n+1 peaks.
What is a caveat to the n+1 rule?
Do not include protons attached to oxygen or nitrogen
The magnitude of splitting is measured in ________, and is called what?
hertz; coupling constant, j
The splitting of the peak represents the number of ____________ hydrogens. A peak will be split into n+1 subpeaks, where n is the number of ____________ hydrogens.
adjacent; adjacent
The deshielded aldehyde has a chemical shift at ____ to ____ ppm.
9 to 10
The even more deshielded carboxylic acid is between ____ to ____ ppm downstream from TMS.
6.0 and 8.5
sp3 hybridized carbons are ____ to ____ ppm and ________ if EWG are present.
0.0 to 3.0
sp2 hybridized carbons are ____ to ____ ppm.
4.6 to 6.0
sp-hybridized carbons are ____ to ____ ppm.
2.0 to 3.0
The more electron density that is pulled away from the proton, the more deshielded it will be and the further ________ the proton will apear.
downfield
____________ is the transfer of a dissolved compound (desired product) from a starting solvent into a solvent in which the product is more stable.
extraction
Extraction is based on what fundamental concept?
like dissolves like
When performing extractions, it is important to make sure that the 2 solvents are ________________, meaning that they form 2 layers that do not mix.
immiscible
When 2 solvents are mixed together, the polar solute will transfer to the water layer, called the ____________ phase. The nonpolar solute becomes the ____________ phase.
aqueous; organic
The aqueous and organic phases separate on their own, and you use a ____________ ________ to isolate them.
separatory funnel
Once the desired product has been isolated in the solvent, you can evaporate the solvent using a ____________ ____________.
rotary evaporator
you can then remove unwanted impurities by using a small amount of solvent to extract and remove. this is a ____.
wash
____________ isolates a solid from a liquid.
filtration
At the end of filtration, one is left with the solid, called the ____________, and the flask full of liquid that passed through the filter, known as the ____________.
residue; filtrate
________ filtration, in which the solvent’s own weight pulls it through the filter, is commonly used when the product of interest is in the filtrate.
gravity
________ filtration, in which the solvent is forced through the filter by a vacuum connected to the flask, is more often used when the solid is the desired product.
vacuum
____________ is a method for further purifying crystals in solution. The product is dissolved in a minimum amount of hot solvent and cooled to ____________, which excludes the impurities once it cools.
recrystallization; recrystallize
____________ takes advantage of differences in the boiling point to separate 2 liquids by evap and condensation.
distillation
________ distillation is only used for separating liquids that boil below 150 degrees C, and have at least a 25 degree difference in boiling points.
simple
The appartus for simple distillation is a distilling ________ containing the combined liquid solution, a distillation ____________ consisting of a thermometer and a ____________, and a ____________ flask to collect the distillate.
flask, column, condenser, receiving
____________ occurs when a liquid is heated to a temperature above its boiling point without vaporization.
superheating
____________ distillation can be used to distill a liquid with a boiling point over 150 C. How does it work?
vacuum; decreasing ambient pressure decreases temperature that liquid needs to reach to have sufficient vapor pressure to boil
To separate liquids with similar boiling points (less than 25 C), we use ____________ distillation.
fractional
A fractionation column connects the distillation flask to the condenser. A fractinoation column is a column in which ________ ________ is increased by the inclusion of inert objects like glass beads or steel wool.
surface area
As vapor rises up the column, it condenses on these surfaces and ____________ back down until rising heat causes it to evaporate again, only to condense again higher in the column.
refluxes
Each time the condensate evaporates, the vapor consists of a ____________ proportion of the compound with the lower boiling point. By the time the top of the column is reached, only the ____________ product drips down to the receiving flask.
higher; desired
The process of chromatography begins by placing the sample onto a solid medium called the ________________ phase, or ____________. We then run the ________ phase, usually a liquid (or a gas in gas chromatography) through the stationary phase.
stationary, adsorbent; mobile
Depending on the characteristics of substances in the sample and the polarity of the mobile phase, it will adhere to the stationary phase with differeing strengths, causing different migration speeds. This is called ____________.
partioning
What are two common materials for stationary phases?
silica gel and cellulose
Chromatography is based on the ________ at which compounds move through media. We typically measure what?
speed; 1. how long it takes to elute or 2. how far it goes
For TLC and paper chromatography, the sample we want to separate is placed directly onto the adsorbent itself. This is ____________. The plate is the ndeveloped, which involves placing the adsorbent upright in a developing chamber. There is a pool of solvent called ____________. The stationary phase is typically silica gel, which is ________.
spotting; eluent; polar
________-________ chromatography uses a nonpolar stationary phase. This means polar solvents move quickly up.
reverse phase
Reverse-phase chromatography uses ____________ light.
ultraviolet
WHen TLC is performed, compounds are generally identified using the ____________ factor, which is relatively constant for a particular compound in a given solvent.
retardation
Retardation factor is calculated using what equation?
Rf = distance spot moved / distance solvent front moved
____________ chromatography uses an entire column filled with silica or aluminum beads as an adsorbent, allowing for much greater separation.
column
TLC uses ____________ ________ to move the solvent up the plate, whereas column chromatography uses ____________.
capillary action; gravity
In column chromatography, the different fractions that leave the column can be collected over time. They contain what?
different compounds
In ________-____________ chromatography, the beads in the column are coated with charged substances so that they attract/bind compounds that have an opposite charge.
ion-exchange
In ________-____________ chromatography, the beads used in the column contain tiny pores of varying sizes. These tiny pores allow small compounds to enter the beads, thus slowing them down.
size-exclusion
In ____________ chromatography, a protein of interest is bound by creating a column with high affinity for that protein. It is accomplished by coating beads with a ____________ that binds the protein or a specific ________ to the protein.
affinity; receptor; antibody
________ chromatography uses gas as an eluent. The adsorbent is a crushed ________ or ________ inside a 30 ft column. The injected compounds must be ____________.
gas; metal or polymer; voltaile
It is common to separate molecules using gas chromatography then inject pure molecules into a ________ ________________ for molecular weight determination.
mass spectrometer
________-____________ ________ chromatography was uses liquid as an eluent and it travels through a column of a defined composition. The compounds pass through a detector and are collected as the solvent flows out of the end of the apparatus.
high-performance liquid
