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Instrumental Chemistry > Exam 2 > Flashcards

Exam 2 Flashcards

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1
Q

Molecules

A

Have covalent bonds

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2
Q

Hybrid Molecules

A

Have both covalent and non-covalent bonding, the part of these hybrids that have the covalent bonds are molecules.

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3
Q

Covalent Bonds

A

Sharing of electrons, changes the energy diagrams by creating hybridized orbitals; ex) sp, sp2, sp3, etc.)

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4
Q

To cause an emission….

A

An electron must be excited to a higher energy state.

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5
Q

The stokes shift can be observed when…..

A

Fluorescence and adsorption are graphed on the same plot.

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6
Q

Beers Law

A

Demonstrates relationship between absorbance and concentration

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7
Q

Beers Law Formula

A

A = Ebc

A = absorbance
E = absorptivity constant 
b = path length (length of cuvette, ~1 cm)
c = concentration
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8
Q

Transmittance Formula

A

A = -logT

A = absorbance
T = transmittance
To find T, use 10^-A

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9
Q

Percent Transmittance

A

%T = P/P0 x100

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10
Q

Absorbance System

A

Source —P0–> Sample —P—> Detector

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11
Q

Graph of Absorbance/Transmittance

A

Linear graph
Y=my+b , A=Ebc

Y = A
m = Eb
x = c
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12
Q

IR Spectroscopy:

Infrared radiation interraction with a molecule is………

A

NOT enough to excite an electron to a new energy state; however vibrational bands can be accessed.

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13
Q

IR Spectroscopy:

Infrared energy is absorbed so…….

A

It does NOT make it to the detector.

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14
Q

IR Spectroscopy:

In order for IR energy to be absorbed……

A

The dipole moment must be changed.

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15
Q

IR Spectroscopy:

The greater the dipole moment…..

A

The greater the peak.

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16
Q

IR Spectroscopy:

2 Factors of Peak Intensity:

A
  1. Vibrations from stretching/bending (stretching generally gives larger peaks)
  2. Electronegativity differences between atoms involved in the bond (the larger the electronegativity difference, the larger the peak)
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17
Q

IR Spectroscopy:

Strong Peak

A

Tall peak, low transmittence

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18
Q

IR Spectroscopy:

Weak Peak

A

Short peak, high transmittance

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19
Q

IR Spectroscopy:

Medium Peak

A

Peak is at mid-height

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20
Q

IR Spectroscopy:

Broad Peak

A

Very large peak base exists across many wavelengths; involves several energies and several bonds that are related.

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21
Q

Functional Groups:

Alcohol

A

R—OH

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22
Q

Functional Groups:

Ether

A

R—O—R

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23
Q

Functional Groups:

Aldehyde

A

R—C—H
II
O

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24
Q

Functional Groups:

Amine

A

R—NH2

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25
Q

Functional Groups:

Carboxylic Acid

A

R—C—OH
II
OH

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26
Q

Functional Groups:

Ester

A

R—C—O—R
II
O

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27
Q

Functional Groups:

Ketone

A

R—C—R
II
O

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28
Q

Functional Groups:

Amides

A

R—C—NH2
II
O

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29
Q

Larger bases indicate…..

A

ACIDS

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30
Q

IR Spectroscopy:

Location of Carbonyl Peak

A

~1700

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31
Q

IR Spectroscopy:

Location of Alcohols

A

~3300

- rounded peak

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32
Q

IR Spectroscopy:

Location of Alkanes

A

Slightly under 3000 cm-1

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33
Q

IR Spectroscopy:

Location of Carboxylic Acids

A

~3000 ish

- wide peak base with sharp peak point

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34
Q

IR Spectroscopy:

Location of Alkenes

A

Slightly above 3000 cm-1

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35
Q

IR Spectroscopy:

Location of Alkynes

A

~3300 cm-1

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36
Q

IR Spectroscopy:

Location of Aldehyde

A

Contains a carbonyl (C=O) at ~1700 cm-1

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37
Q

IR Spectroscopy:

Location of Ether

A

~1050 - 1300 cm-1

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38
Q

IR Spectroscopy:

Location of Ester

A

Contains carbonyl group (C=O) at ~1700 cm-1

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39
Q

IR Spectroscopy:

Location of Amine

A

Large, wide based, curved peak around 3000 and greater,

Contains many curved peaks

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40
Q

IR Spectroscopy:

Location of Amide

A

Multiple peaks with large base peaks (one larger than 3000, one ~1700)

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41
Q

IR Spectroscopy:

Location of Benzene Ring

A

Narrow, thin peaks

Three located at ~3000, ~1400, ~900

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42
Q

IR Spectroscopy:
Location of Ring
(Single bonds only)

A

Narrow, thin peaks
VERY LARGE peak at ~2900
Other peaks at ~1400, small peaks at ~900

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43
Q

Steps in NMR:

A
  1. Align all of the nuclei
  2. Blast them all with energy
  3. See what happens
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44
Q

FID

A

Free Induction Decay
Generated when nuclei return to their ground state
(Different nuclei will return to their ground states at different rates depending on its surroundings)

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45
Q

How to generate NMR spectra (frequency vs. intensity) from FID:

A

Use Fourier transform to pull wave functions apart into frequency vs. intensity.

FOURIER TRANSFORM

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46
Q

What does information does FTIR give you?

A

FUNCTIONAL GROUPS

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47
Q

What information does H-NMR give you?

A

Types and number of equivalent protons and nearby protons

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48
Q

What information does C-NMR give you?

A

Types and number of equivalent carbons

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49
Q

What information does Mass Spec give you?

A

Molecular mass and groups that can fall from the larger structure

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50
Q

Peak splitting is dependent on…..

A

Nearby protons; only for H-NMR (proton) spectra

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51
Q

Duderated

A

All hydrogen’s are one mass unit greater

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52
Q

What does mass spectrometry measure?

A

Mass to charge ratio

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53
Q

Infrared Radiation (IR) causes…….

A

VIBRATIONAL STATE CHANGES

IR is not strong enough to cause band gap jumps

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54
Q

IR Active = ?

Raman Active = ?

A

IR Active = dipole moment change

Raman Active = NO dipole meant change

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55
Q

KNOW THE VIBRATIONAL VARIATIONS

Bond Stretching and Bending

A

Stretching = symmetric vs. asymmetric

Bending = in-plane rocking vs. in-plane scissoring
= out-of-plane wagging vs. out-of-plane twisting

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56
Q

Harmonic Oscillator

A

How the energy of the vibrational mode can be seen

E = (v + 1/2) h Vm

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57
Q

Degrees of Freedom =

A

= 3N

58
Q

Degrees of Freedom

A

How you can deduce the number and kind of vibrations in simple systems

59
Q

How to Calculate Degrees of Freedom:

A

A molecule containing N atoms is said to have 3N degrees of freedom (3*N)

60
Q

3 Different Types of Degrees of Freedom:

A

A. Translational - motion of the entire molecule thru space
B. Rotational - motion of entire molecule around its center of gravity
C. Vibrational - motion of each of its atoms to the other atoms

61
Q

How to Calculate Vibrational Degrees of Freedom:

A

3N - 6

3N - 5 for LINEAR molecules

62
Q

4 Things that give less Degrees of Freedom than expected:

A
  1. No change in dipole moment (due to symmetry of molecules)
  2. The energies of 2 or more vibrations are identical (or nearly identical)
  3. The absorption intensity is so low that it is undetectable
  4. The vibrational energy is in a wavelength region beyond the instrument’s range
63
Q

Vibrations are not completely separate……

A

They interact with each other.

64
Q

Rules of Vibrational Coupling:

A

A. Strong coupling between stretch vibrations occurs only when there is an atom common to the 2 vibrations.

B. Interaction between bending vibrations requires a common bond between the vibrating groups.

C. Coupling between a stretching and bending vibration can occur if the stretching bond forms one side of the angle that varies in the bending vibration.

D. Interaction is greatest when the coupled groups have individual energies that are nearly equal.

E. Little or no interaction is observed between groups separated by 2 or more bonds.

F. Coupling requires that the vibrations be of the same symm. species.

65
Q

Layout of FTIR:

A
  • the laser is NOT the source; it is only a guide.

- interferometer is a critical piece.

66
Q

Interferometer

A

Device that separates a beam of light by reflection, then recombines them causing interference; used to measure wavelength and index of refraction

67
Q

NMR Spectroscopy

A

Nuclear Magnetic Resonance Spectroscopy

68
Q

What frequency region does NMR use?

A

Radio frequency region

69
Q

Example of NMR in practical use

A

MRI

70
Q

4 Important Nuclei in NMR Spectroscopy:

A

H1
C13
F19
P31

71
Q

Why does spinning matter in NMR Spectroscopy?

A
  • nuclei are charged and spin
  • charged stuff that spins generates a magnetic field
  • gives magnetic quantum number
72
Q

Bolzmann’s Distribution of States

A

Statistical probability for the population of each of the states

Nj/No = exp (-deltaE / KT)

(Delta E is the energy levels generated by the magnetic moment; magnet dependent)

73
Q

Application of Radio Waves during NMR Spectroscopy:

A

Hitting system with radio waves of a particular frequency can cause the energy level to jump

74
Q

Spin-Lattice Relaxation has to do with…..

A

PEAK LOCATION

75
Q

Spin-Spin Relaxation has to do with…..

A

PEAK SPLITTING

76
Q

Lattice

A

The entire collection of atoms that constitute a sample; atoms are constantly in motion which creates a magnetic field around the atoms

77
Q

Spin-Lattice Relaxation:

A

All magnetic field interact and will convert almost anything into minuscule temperature adjustments

(1st order exponential decay characterized by a relaxation time, T1)

78
Q

Spin-Spin Relaxation

A

When 2 neighboring nuclei of the same kind have identical relaxation rates but are in different magnetic quantum states, the magnetic fields of each can interact to cause an interchange of states

79
Q

Resolution in NMR:

A
  • spin-lattice can be impacted to spread peaks further apart; peaks shifter further apart at a better resolution
  • spin-spin is NOT affected.
80
Q

Chemical shift is due to…..

A

Spin-lattice coupling

81
Q

Chemical Shift

A

The frequency of the resonance expressed with reference to a standard compound which is defined to be at 0 ppm

82
Q

Screening

A

Detection of fragments from NMR, which can be used to determine the overall structure

83
Q

Shielding

A

When a nucleus’s chemical shift has been decreased due to addition of electron density or change in magnetic field

84
Q

Splitting

A

Occurs as the magnetic field of 2 adjacent nuclei interact, which pushes electrons around the structure. The movement of electrons produces changes in the magnetic field.

85
Q

Necessary Parts of NMR instrument:

A
  • magnets (need to be very cold)
  • shimming coils (shims)
  • homogeneity of the order of 10^-9
86
Q

How the magnets in an NMR instrument cooled?

A

Liquid nitrogen and liquid helium

87
Q

Phasing

A

The modification of a peak to increase resolution in NMR

88
Q

Phasing can cause…..

A

Upside down peak in NMR spectra; can also get rid of inverted peaks as well

89
Q

Goal of shimming coils (shims) in NMR instrument:

A

To create a homogenous magnetic field

90
Q

Results of Shimming:

A
  • impacts resolution (poorly shimmed = loss of resolution)
91
Q

Mass Spectrometry is able to…..

A
  1. Give elemental composition
  2. Give structural info about the inorganic, organic, and biological molecules
  3. Gives qualitative and quantitative info about complex mixtures
  4. Gives structure and composition of solid surfaces
  5. Gives isotope ratios of atoms in a sample
92
Q

Mass Spec data output:

A
  • x-axis is mass/charge

- y-axis is relative intensity; values depend on instrument parameters

93
Q

Ions…..

A

Can be detected as either positive or negative

94
Q

Important parts of Mass Spec:

A
  1. Sample Inlet
  2. Ion sources
  3. Ion transfers
  4. Mass Analyzers
  5. Detector
  6. Recorder
95
Q

Mass Spec:

Generic function of Sample Inlet

A

Introduces the sample

96
Q

Mass Spec:

Generic function of ion sources

A

Ionizes

97
Q

Mass Spec:

Generic function of ion transfers

A

Transfers ions

98
Q

Mass Spec:

Generic function of mass analyzers

A

Separates ion stream into something useful

99
Q

Mass Spec:

Generic function of detector

A

Converts info to electrical domain

100
Q

Mass Spec:

Generic function of recorder

A

Records infromation

101
Q

Mass Spec:

Type of sample inlet is dependent on….

A
  1. Sample phase (s/l/g)
  2. Sample composition (pure/mixture)
  3. Sample stability
102
Q

Mass Spec:

Which type of sample is most convenient?

A

GAS SAMPLES

103
Q

Mass Spec:

Which type is used to analyze gas samples?

A

GCMS

Gas Chromatography Mass Spec

104
Q

Mass Spec:

How are liquids analyzed?

A

Nebulization is used as an ion source since the molecules in a liquid are closer together, therefore there are more of them

105
Q

Mass Spec:

What type is used to run liquid samples?

A

HPLC-MS

High Pressure Liquid Concentration Mass Spec

106
Q

Mass Spec:

What type is used to analyze solid samples?

A

MALDI - most common
(Matrix Assisted Laser Desorption/Ionization)

ASAP (Atmospheric Solids Analysis Probe)

107
Q

Hard Ion Source

A

Something that applies a lot of energy to a system fast; leaves a large amount of energy in the molecules
INCREASES FRAGMENTATION

108
Q

Soft Ion Source

A

Something that gently applies energy to a system; puts just enough energy into a molecules to attach a charge
INCREASES STABILITY OF IONIZED SPECIES

109
Q

The larger the molecule….. the _______ the ionization technique required.

A

SOFTER

110
Q

MALDI

A

Matrix Assisted Laser Desorption/Ionization

  • soft technique
  • mass spec used to analyze solid samples
111
Q

Ion Source:

EI

A

Electron Impact (mass spec)

  • hard ionization
  • good for small molecules
112
Q

Ion Source:

ESI

A

Electro spray Ionization (Mass Spec)

  • soft ionization
  • good for proteins
113
Q

FAB

A

Fast Atom Bombard (mass spec)

  • semi hard ionization
  • good for proteins and sugars
114
Q

Skimmers

A
  • important part of mass spec.

- interface between vacuum chambers used to thin out solvent

115
Q

3 Categories of Mass Analyzers

A
  1. Quadripole
  2. Time of Flight
  3. Double Focusing/Magnetic Sector
116
Q

Quadripole

A
  • type of mass analyzer in mass spec
  • design: linear, allows only ions you want to pass thru
  • combination of DC current and RF frequency to alter trajectories of ions
  • advantages: fast, small, able to use multiple sources
117
Q

Traps

A

Mass analyzer in mass spec.

  • traps desired ions in center of electromagnetic field
  • advantage: can do multiple MS/MS
  • disadvantage: lose a lot of sample
118
Q

Time of Flight

A
  • type of mass analyzer
  • time it takes for an ion to migrate a set distance
  • ions are formed, then spread are arrive at the detector at different times due to differing velocities.
119
Q

Double Focusing/Magnetic Sector

A
  • Type of mass analyzer in mass spec.

- ions are accelerated down a curved flight tube, magnets deflect trajectory

120
Q

Advantage and Disadvantage of Double Focusing:

A

Ad: easily reproduced
Dis: expensive

121
Q

Advantage and Disadvantage of Time of Flight:

A

Ad: great for large molecules
Dis: low reproducibility

122
Q

Advantage and Disadvantage of Traps:

A

Ad: multiple ms/ms/ms/ms on trapped ions
Dis: lose a lot of sample each time

123
Q

Transduction

A

Detection process; converts domain

124
Q

Faraday Cup

A

Transduction in Mass Spec

- blocks signals, making it easy to detect charge

125
Q

Electron Multiplier

A

Transduction in Mass Spec.

  • device that uses a series of dynodes
  • cascade of electrons generates a measurable electrical current
126
Q

Photocathode

A

Converts light to electricity

127
Q

Array Transducers

A

Transduction in Mass Spec.

  • used to detect multiple ions that have been separated spatially
  • works on time of flight and double focusing instruments
  • includes micro channel plates, microfaraday array
128
Q

Mass Spec stands for

A

Mass Spectrometry

129
Q

Tandem Techniques

A

Any technique that involves running MS followed by MS

- most common is the triple quad and QTOF

130
Q

Ionization in Atomic vs. Molecular vs. Biomolecules Mass Spec.’s

A

Atomic MS = hard ionization
Molecular MS = hard, but softer than atomic
Biomolecule MS = soft

131
Q

Ion Mobility Instruments

A

Separates ions based on their mobility

132
Q

PTR-MS

A

Soft ionization; ionizes protons and allows them to interact with analyte

133
Q

Ion Sources:

APCI

A

Atmospheric Pressure Chemical Ionization

  • soft ionization
  • used in trace analysis detection of steroids, pesticides, etc.
134
Q

Ion Sources:

DESI

A

Desorption Electrospray Ionization

- used for chemical analysis of atmospheric conditions

135
Q

Ion Source:

PI

A

Photoionization

- used to investigate chemistry of low pressure flames

136
Q

Ion Source:

SIMS

A

Secondary Ion Mass Spectrometry

- determines the elemental composition of a surface, VERY SENSITIVE

137
Q

Ion Source:

LD

A

Laser Desorption

- soft ionization

138
Q

Ion Source:

DART

A

Direct Analysis in Real Time

- can be used to analyze solids, liquids, and gases

139
Q

Ion Source:

LTP

A

Low Temperature Plasma

140
Q

Deshielding

A

when a nucleus’s chemical shift has been increased due to the removal of electron density or change in magnetic field

Instrumental Chemistry (5 decks)

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