Chapter 11: Spectroscopy and Chapter 12: Separations and Purifications

Question 1

What does spectroscopy measure?

Answer 1

The energy differences between the possible states of a molecular system

Question 2

How does spectroscopy work?

Answer 2

Determining the frequencies of EM radiation absorbed by the molecules

Question 3

What does infrared (IR) spectroscopy measure?

Answer 3

Molecular vibrations

Question 4

How is an IR spectrum recorded?

Answer 4

IR light is passed through a sample, and the absorbance is measured

Question 5

By determining what bonds exist within a molecule, we hope to infer what?

Answer 5

The functional groups in the molecule

Question 6

The useful absorptions for spectroscopy occur at wavelengths of what?

Answer 6

2500 to 25,000 nm

Question 7

On an IR spectrum, we use an analog of frequency called ____________.

Answer 7

wavenumber

Question 8

When light of these wavenumbers is absorbed, what happens to the molecules?

Answer 8

They enter excited vibrational states.

Question 9

What are 4 types of vibration that can occur?

Answer 9

1. symmetric bend
2. asymmetric bend
3. symmetric stretch
4. asymmetric stretch

Question 10

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.

Answer 10

1500 to 400 cm-1 range; the fingerprint region

Question 11

For an absorption to be recorded, the vibration must result in a change in the ____________ ____________ ____________.

Answer 11

bond dipole moment

Question 12

Which molecules do not have recordable absorptions?

Answer 12

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

Question 13

The hydroxyl group absorbs with a ________ peak at around one of two frequencies: ________ cm^{-1 for alcohols, and ________ cm-1 for carboxylic acids.}

Answer 13

broad; 3300, 3000

Question 14

The carbonyl of a carboxylic acid pulls some of the electron density out of the OH bond, shifting the absorption to a ____________ wavenumber.

Answer 14

lower

Question 15

The carbonyl absorbs around ________ cm^{-1 with a ________ peak.}

Answer 15

1700; sharp

Question 16

The bond between any atom and hydrogen always has a relatively ________ absorption frequency. As we add more bonds between carbon atoms, the absorption frequency ____________.

Answer 16

high; increases

Question 17

N-H bonds are in the same region as O-H bonds at ________ cm^{-1 but have a ________ peak instead of a ________ one.}

Answer 17

3300; sharp instead of broad

Question 18

IR spectra are plotted as percent ________________, the amount of light that passes through the sample and reaches the detector, vs. wavenumber.

Answer 18

transmittance

Question 19

UV spectra are obtained by passing ________ light through a sample that is usually dissolved in an inert, nonabsorbing solvent, and recording the ____________.

Answer 19

absorbance

Question 20

UV spectra plot what?

Answer 20

absorbance against wavelength

Question 21

The most significant piece of info we get from UV spectroscopy is the ____________ of ____________ ____________, which tells us what?

Answer 21

wavelength of maximum absorbance; the extent of conjugation within conjugated systems

Question 22

The more conjugated a compound is, the ________ the energy of the transition and the ________ the wavelength of maximum absorbance.

Answer 22

lower; greater

Question 23

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.

Answer 23

highest; lowest; excited; longer

Question 24

high yield

UV spectroscopy is most useful for studying compounds containing ________ bonds or heteroatoms with ________ ________ that create conjugated systems.

Answer 24

double; lone pairs

Question 25

____________ molecules, or molecules with ____________ p-orbitals, can also be excited by UV light.

Answer 25

conjugated; unhybridized

Question 26

Conjugation shifts the absorption spectrum, resulting in ________ maximum wavelengths.

Answer 26

higher

Question 27

Nuclear magnetic resonance (NMR) spectroscopy is based on the fact that certain atomic nuclei have ____________ ____________ that are oriented at random.

Answer 27

magnetic moments

Question 28

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).

Answer 28

alpha

Question 29

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).

Answer 29

beta

Question 30

What does NMR plot?

Answer 30

frequency vs. absorption of energy

Question 31

NMR uses an arbitrary variable called ____________ ________ with units of parts per million of spectrometer frequency.

Answer 31

chemical shift

Question 32

The chemical shift is plotted on the x-axis, and it ________ toward the left (referred to as ________.

Answer 32

increases; downfield

Question 33

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.

Answer 33

TMS

Question 34

NMR is most commonly used to study what?

Answer 34

^{1H nuclei (protons)}

Question 35

Any atom with a ________ ________ (an odd atomic number, odd mass number, or both) can be studied with NMR.

Answer 35

nuclear spin | MCAT only tests 1H NMR

Question 36

Most hydrogen (^{1H) nuclei come into resonance ____ to ____ ppm downfield from TMS.}

Answer 36

0 to 10

Question 37

Each distinct set of nuclei gives rise to a ____________ peak.

Answer 37

separate

Question 38

This means that if multiple protons are ____________ ____________, having the same magnetic environment, they will lead to the same peak.

Answer 38

chemically equivalent

Question 39

The height of each NMR peak is proportional to what?

Answer 39

The number of protons it contains ## Footnote The ratio of the protons correponds to the ratio of protons produced at each peak

Question 40

Each peak or group of peaks that are part of a multiplet represents what?

Answer 40

A single group of equivalent protons

Question 41

The relative area of each peak reflects what?

Answer 41

The ratio of protons producing each peak

Question 42

The position of an NMR peak is due to what?

Answer 42

Shielding and deshielding effects

Question 43

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?

Answer 43

A reading further downfield

Question 44

If we had an EDG, it would shield the nuclei and give it a position further ________.

Answer 44

upfield

Question 45

Everything in proton NMR will be more ____________ than TMS, thus it will be ____________.

Answer 45

deshieleded; downfield

Question 46

When we have 2 protons in close proximity that are not magnetically identical, ____-____ ____________ (____________) occurs.

Answer 46

spin-spin coupling (splitting | (hydrogens on two adjacent atoms -- within 3 bonds of each other)

Question 47

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.

Answer 47

doublet

Question 48

TO determine the number of peaks present, we use the ________ rule.

Answer 48

n + 1

Question 49

What does the n+1 rule state?

Answer 49

If a proton has n protons that are 3 bonds away, it will be split into n+1 peaks.

Question 50

What is a caveat to the n+1 rule?

Answer 50

Do not include protons attached to oxygen or nitrogen

Question 51

The magnitude of splitting is measured in ________, and is called what?

Answer 51

hertz; coupling constant, j

Question 52

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.

Answer 52

adjacent; adjacent

Question 53

The deshielded aldehyde has a chemical shift at ____ to ____ ppm.

Answer 53

9 to 10

Question 54

The even more deshielded carboxylic acid is between ____ to ____ ppm downstream from TMS.

Answer 54

6.0 and 8.5

Question 55

sp3 hybridized carbons are ____ to ____ ppm and ________ if EWG are present.

Answer 55

0.0 to 3.0

Question 56

sp2 hybridized carbons are ____ to ____ ppm.

Answer 56

4.6 to 6.0

Question 57

sp-hybridized carbons are ____ to ____ ppm.

Answer 57

2.0 to 3.0

Question 58

The more electron density that is pulled away from the proton, the more deshielded it will be and the further ________ the proton will apear.

Answer 58

downfield

Question 59

____________ is the transfer of a dissolved compound (desired product) from a starting solvent into a solvent in which the product is more stable.

Answer 59

extraction

Question 60

Extraction is based on what fundamental concept?

Answer 60

like dissolves like

Question 61

When performing extractions, it is important to make sure that the 2 solvents are ________________, meaning that they form 2 layers that do not mix.

Answer 61

immiscible

Question 62

When 2 solvents are mixed together, the polar solute will transfer to the water layer, called the ____________ phase. The nonpolar solute becomes the ____________ phase.

Answer 62

aqueous; organic

Question 63

The aqueous and organic phases separate on their own, and you use a ____________ ________ to isolate them.

Answer 63

separatory funnel

Question 64

Once the desired product has been isolated in the solvent, you can evaporate the solvent using a ____________ ____________.

Answer 64

rotary evaporator

Question 65

you can then remove unwanted impurities by using a small amount of solvent to extract and remove. this is a ____.

Answer 65

wash

Question 66

____________ isolates a solid from a liquid.

Answer 66

filtration

Question 67

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 ____________.

Answer 67

residue; filtrate

Question 68

________ 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.

Answer 68

gravity

Question 69

________ 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.

Answer 69

vacuum

Question 70

____________ 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.

Answer 70

recrystallization; recrystallize

Question 71

____________ takes advantage of differences in the boiling point to separate 2 liquids by evap and condensation.

Answer 71

distillation

Question 72

________ distillation is only used for separating liquids that boil below 150 degrees C, and have at least a 25 degree difference in boiling points.

Answer 72

simple

Question 73

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.

Answer 73

flask, column, condenser, receiving

Question 74

____________ occurs when a liquid is heated to a temperature above its boiling point without vaporization.

Answer 74

superheating

Question 75

____________ distillation can be used to distill a liquid with a boiling point over 150 C. How does it work?

Answer 75

vacuum; decreasing ambient pressure decreases temperature that liquid needs to reach to have sufficient vapor pressure to boil

Question 76

To separate liquids with similar boiling points (less than 25 C), we use ____________ distillation.

Answer 76

fractional

Question 77

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.

Answer 77

surface area

Question 78

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.

Answer 78

refluxes

Question 79

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.

Answer 79

higher; desired

Question 80

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.

Answer 80

stationary, adsorbent; mobile

Question 81

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 ____________.

Answer 81

partioning

Question 82

What are two common materials for stationary phases?

Answer 82

silica gel and cellulose

Question 83

Chromatography is based on the ________ at which compounds move through media. We typically measure what?

Answer 83

speed; 1. how long it takes to elute or 2. how far it goes

Question 84

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 ________.

Answer 84

spotting; eluent; polar

Question 85

________-________ chromatography uses a nonpolar stationary phase. This means polar solvents move quickly up.

Answer 85

reverse phase

Question 86

Reverse-phase chromatography uses ____________ light.

Answer 86

ultraviolet

Question 87

WHen TLC is performed, compounds are generally identified using the ____________ factor, which is relatively constant for a particular compound in a given solvent.

Answer 87

retardation

Question 88

Retardation factor is calculated using what equation?

Answer 88

Rf = distance spot moved / distance solvent front moved

Question 89

____________ chromatography uses an entire column filled with silica or aluminum beads as an adsorbent, allowing for much greater separation.

Answer 89

column

Question 90

TLC uses ____________ ________ to move the solvent up the plate, whereas column chromatography uses ____________.

Answer 90

capillary action; gravity

Question 91

In column chromatography, the different fractions that leave the column can be collected over time. They contain what?

Answer 91

different compounds

Question 92

In ________-____________ chromatography, the beads in the column are coated with charged substances so that they attract/bind compounds that have an opposite charge.

Answer 92

ion-exchange

Question 93

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.

Answer 93

size-exclusion

Question 94

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.

Answer 94

affinity; receptor; antibody

Question 95

________ chromatography uses gas as an eluent. The adsorbent is a crushed ________ or ________ inside a 30 ft column. The injected compounds must be ____________.

Answer 95

gas; metal or polymer; voltaile

Question 96

It is common to separate molecules using gas chromatography then inject pure molecules into a ________ ________________ for molecular weight determination.

Answer 96

mass spectrometer

Question 97

________-____________ ________ 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.

Answer 97

high-performance liquid