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Chem 409 > Chapter 4 - Experimental techniques > Flashcards

Chapter 4 - Experimental techniques Flashcards

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1
Q

Analyte

A

The component being analyzed in a system.

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2
Q

Recrystallization

A

A purification step involving the dissolution and crystallization of a solid from a solvent or solvent mixture.

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3
Q

Atomic absorption spectroscopy (AAS)

A

The quantitative determination of a metal carried out by observing the diagnostic absorption spectrum of gaseous atoms of the metal.

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4
Q

Thermogravimetric analysis (TGA)

A

In TGA, the change in mass of a sample is monitored as the sample is heated.

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5
Q

Solvate

A

A compound formed by the interaction of a solute with a solvent.

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6
Q

Fast atom bombardment (FAB)

A

Ions are produced by bombarding the sample (neutral molecules or ionic salts) with high energy xenon or argon atoms. It is a soft technique.

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7
Q

Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF)

A

A UV laser is used to generate atoms, M, of the sample, and [M+H]+ or [M+Na]+ ions are typically detected. It is a soft technique.

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8
Q

IR and Raman spectroscopies are concerned with

A

transitions between vibrational energy levels.

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9
Q

For a vibrational mode to be IR active, it must

A

give rise to a change in dipole moment.

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10
Q

For a vibrational mode to be Raman active, it must

A

give rise to a change in polarizability.

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11
Q

Zero point energy

A

corresponds to the energy of a molecule’s lowest vibrational level (vibrational ground state).

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12
Q

Simple harmonic oscillator equation

A

Ev = (v + 1/2)hv (the last v is nu, frequency)
first v = energy level

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13
Q

The vibrational frequency of the bond XY depends on

A

the masses of X and Y, and the force constant, k.

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14
Q

Wavenumber equation for IR spectra

A 
wavenumber = 1/(2pi(c)) sqrt(k/u)
c = speed of light
k = force constant
u = reduced mass (mu)
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15
Q

IR region

A

Far IR = 20 cm-1
Near IR = 14000 cm-1
Mid IR = 400-4000 cm-1

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16
Q

Rayleigh scattering

A

When radiation of a frequency, v0, falls on a vibrating molecule, most of the radiation is scattered without a change in frequency.

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17
Q

Electronic spectroscopy

A

is concerned with transitions of electrons between energy levels and covers both absorption and emission spectroscopies.

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18
Q

Electronic spectra arise from

A

transitions of electrons between energy levels.

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19
Q

Transitions from lower to higher energy levels produce

A

absorption spectra.

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20
Q

Transitions from higher to lower energy levels produce

A

emission spectra.

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21
Q

Franck-Condon approximation

A

states that electron transitions are very much faster than nuclear motion; thus, an electronic transition occurs without any significant change in the positions of the nuclei in a molecule giving rise to a so-called ‘vertical transition.’

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22
Q

A UV-VIS spectrophotometer typically records absorption spectra in the ________ range.

A

200-800 nm

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23
Q

Transmittance (T)

A

the ratio of the intensity of the transmitted radiation (I) to that of the incident radiation (I0).

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24
Q

Absorbance equation

A

A = -logT = -log(I/I0)

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25
Q

E (epsilon)

A

molar extinction (or absorption) coefficient

26
Q

Bathochromic effect (red shift)

A

a shift in an absorption towards the red end of the spectrum (longer wavelengths, lower energy).

27
Q

Hypsochromic effect (blue shift)

A

a shift in an absorption towards the blue end of the spectrum (shorter wavelength, higher energy).

28
Q

Luminescence

A

The spontaneous emission of radiation from an electronically excited species. Covers both fluorescence and phosphorescence.

29
Q

Nuclear magnetic resonance spectroscopy.

A

A resonance technique involving absorption of radiofrequency energy.

30
Q

3 main criteria for suitable nuclei for NMR

A

1) The nucleus possesses a value of the nuclear spin quantum number I greater than or equal to 1/2.
2) The nucleus should occur in significant abundance (advantageous, but not essential)
3) The nucleus possess a relatively short spin-relaxation time (T1).

31
Q

More positive (less negative) chemical shifts

A

= higher frequency = downfield (older term)

32
Q

Less positive (more negative) chemical shifts

A

= lower frequency = upfield (older term)

33
Q

Standard reference for 1H and 13 C NMR spectroscopies.

A

tetramethylsilane = SiMe4 (TMS)

34
Q

Samples for solution NMR spectroscopy are generally prepared using

A

deuterated solvents.

35
Q

The number of spins of attached nuclei determine the

A

multiplicity (number of lines) and patter of the NMR spectroscopic signal of the observed nucleus.

36
Q

Multiplicity equation

A

Multiplicity (number of lines) = 2nI + 1
the nucleus being observed is coupled to n equivalent nuclei with quantum number I.

37
Q

Redistribution reaction

A

one in which substituents exchange between species but the types and numbers of each type of bond remain the same.

38
Q

Electron paramagnetic resonance (EPR) spectroscopy

A

is a resonance technique involving microwave-induced transitions between magnetic energy levels of electrons which possess a net spin and orbital angular momentum.

39
Q

Zeeman electronic effect

A

Under an applied magnetic field, B0, the interaction between an unpaired electron and the magnetic field results in a splitting of the energy levels.

40
Q

X-band frequency

A

9-10 GHz

41
Q

L-band frequency

A

1-2 GHz

42
Q

S-band frequency

A

2-4 GHz

43
Q

Q-band frequency

A

35 GHz

44
Q

W-band frequency

A

95 GHz

45
Q

Gamma energy range for Mossbauer spectroscopy

A

10-100 keV

46
Q

The Mossbauer effect is the

A

emission and resonant absorption of nuclear gamma rays studied under conditions such that the nuclei have negligible recoil velocities when gamma ray are emitted or absorbed.

47
Q

The Mossbauer effect is only achieved by working with

A

solid samples in which the nuclei are held rigidly in a crystal lattice.

48
Q

Most abundant isotope used in Mossbauer spectroscopy

A

Iron - 57

49
Q

Isomer shift

A

The velocity of movement required to bring about maximum absorption relative to alpha-iron (defined as arbitrary zero for Iron - 57).

50
Q

In X-ray diffraction (XRD),

A

X-rays are diffracted by electrons surrounding the nuclei in atoms in a crystalline or polycrystalline solid.

51
Q

Monochromatic radiation

A

X-rays of a single wavelength

52
Q

Scattering power depends on

A

the number of electrons in an atom.

53
Q

Bragg’s equation

A

2dsin(theta) = n(lambda)

54
Q

Analysis by single crystal X-ray diffraction leads to

A

the full determination of the structure of a compound.

55
Q

Ideal crystal dimensions for single crystal X-ray diffraction

A

0.1 to 0.3 mm

56
Q

Unit cell

A

The smallest repeating unit in a crystal lattice.

57
Q

1 Angstrom = _____ m

A

10^-10

58
Q

Polymorph

A

Different phases of the same chemical compound with different crystal structures.

59
Q

Powder X-ray diffraction data are routinely used for

A

identifying a bulk sample of a material, and for screening different phases of a compound.

60
Q

In neutron diffraction,

A

Bragg scattering of neutrons occurs when neutrons interact with the nuclei of atoms in a single crystal.

61
Q

Gas phase electron diffraction

A

Electrons are scattered by the electric fields of atomic nuclei in gas phase molecules; intramolecular bond parameters are determined.

62
Q

Photoelectron spectroscopy (PES)

A

is a technique used to study the energies of occupied atomic or molecular orbitals.

Chem 409 (9 decks)

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