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CHM1022 > 3. Spectroscopy > Flashcards

3. Spectroscopy Flashcards

1
Q

What is the Beer-Lambert law?

A

this relates to the absorbance (A) of a solution to the molar absorbance coefficient (ξ) of the absorbing species, the concentration © of the absorbing species and the path length of the cell (l), via the equation A = ξ c L

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2
Q

What is bending?

A

a type of vibration that changes bond angles

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3
Q

What is Chemical shift (δ)?

A

the quantity used in NMR spectroscopy to identify the positions of signals produced by the nuclei of a sample. The unit of chemical shift (δ) is parts per million (ppm)

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4
Q

What is 13C-NMR spectroscopy?

A

Nuclear magnetic resonance spectroscopy of carbon atoms within molecules. It provides information about the carbon-hydrogen framework of a molecule

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5
Q

What is a complex splitting pattern?

A

a splitting pattern resulting from more than one set of equivalent hydrogen atoms. Signals of this type are called multiplets

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6
Q

What is a correlation table?

A

a table of data on spectroscopic absorption patterns of selected functional groups

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7
Q

What does deshielded mean?

A

describes the situation in NMR spectroscopy in which resonance or inductive effects reduce the electron density around a nucleus, thus increasing the ability of an applied magnetic field to bring the nucleus into resonance

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8
Q

What is a doublet?

A

a signal in 1H-NMR spectroscopy that has been split into two peaks in a ratio of 1:1

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9
Q

What does downfield mean?

A

Describe a signal in NMR spectroscopy that is towards the left of the spectrum or of another signal

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10
Q

What is electromagnetic radiation?

A

energy propagated through space in the form of oscillating electric and magnetic fields

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11
Q

What is electron spin resonance (ESR)?

A

a methods of locating electrons within the molecules of a paramagnetic substance

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12
Q

What are equivalent hydrogen atoms?

A

hydrogen atoms that are chemically equivalent

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13
Q

What is the fingerprint region?

A

in infrared spectroscopy, the region of the spectrum from 1000 to 400 cm-1

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14
Q

What is frequency?

A

the number of full cycles of a wave that pass a given point in a second

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15
Q

What is Hertz (Hz)?

A

the SI unit of frequency. One hertz equals one wave cycle per second

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16
Q

What is high resonance mass specroscopy?

A

a technique that allows the precise measurement of the mas to charge ratio of ions

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17
Q

What is 1H-NMR spectroscopy?

A

nuclear magnetic resonance spectroscopy of hydrogen atoms within molecules. It provides information about the carbon-hydrogen framework of a molecule

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18
Q

What is the index of hydrogen deficiency?

A

the sum of the number of rings and π-bonds in a molecule

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19
Q

What does infrared active mean?

A

any vibration that results in the absorption of infrared radiation. For a molecule to absorb infrared radiation, the bond undergoing vibration must be polar and its vibration must cause a periodic change in the bond dipole; the greater the polarity of the bond, the more intense the absorption

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20
Q

What is infrared radiation?

A

the portion of the electromagnetic spectrum with wavelengths in the range 7.8 x 10-7 m to 2.0 x 10-3m

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21
Q

What is integration?

A

a mathematical process used for determining the area under a signal in an NMR spectrum

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22
Q

What are lines of integration?

A

a curved line at a signal on a 1H-NMR spectrum that allows the determination of the relative number of hydrogen atoms giving rise to that signal

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23
Q

What is a local magnetic field?

A

the magnetic field generated by electrons surrounding a nucleus

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24
Q

What is mass spectroscopy?

A

a technique used to determine the mass of molecules and fragments of molecules

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25
Q

What is a molecular ion?

A

an ionised molecule that produces a peak in a mass spectrum. This is usually the peak with the highest m/z value

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26
Q

What is a mulitplet?

A

the splitting pattern of a complex signal in 1H-NMR spectroscopy

27
Q

What is multiplicity?

A

the splitting pattern of a signal in 1H-NMR spectroscopy, which can be described as, singlet, doublet, triplet, quartet, multiplet etc.

28
Q

What is the (n + 1) rule?

A

a rule for determining the splitting patterns in NMR spectroscopy. If hydrogen atom has n other hydrogen atoms that are not equivalent to it, but are equivalent to each other, on the same or adjacent atom(s), its 1H-NMR signal is split into (n+1) peaks

29
Q

What is nuclear magnetic resonance (NMR) spectroscopy?

A

a spectroscopic technique that measures the absorption of energy by nuclei in the presence of a magnetic field

30
Q

What is a quartet?

A

a signal in 1H-NMR spectroscopy that has been split into four peaks in a ratio of 1:3:3:1

31
Q

What is a radical cation?

A

a species with a positive charge and an unpaired electron

32
Q

What is radio-frequency radiation?

A

the portion of the electromagnetic spectrum with wavelengths greater than a metre

33
Q

What is a reference compound?

A

a compound added to a sample to be studied by NMR spectroscopy, usually TMS. The positions of the signals in the spectrum are then compared with those of the reference compound

34
Q

What is resonance?

A

the absorption of electromagnetic radiation by a spinning nucleus and the resulting flip of its nuclear spin state

35
Q

What does shielded mean?

A

describes the situation in NMR spectroscopy in which local magnetic fields from electron surrounding a nucleus decrease the ability of an applied magnetic field to bring the nucleus into resonance

36
Q

What is signal splitting?

A

a phenomenon in NMR spectroscopy in which the 1H-NMR signal from one set of hydrogen atoms is split by the influence of neighbouring non-equivalent hydrogen atoms

37
Q

What is a singlet?

A

a signal in 1H-NMR that has not been split

38
Q

What is a splitting pattern?

A

the pattern obtained when a signal in a 1H-NMR spectrum is split by the influence of neighbouring non-equivalent hydrogen atoms. These can be described as multiplets, singlets, doublets, triplets, quartets etc.

39
Q

What is stretching?

A

a type of vibration that changes bond lengths

40
Q

What is tetramethylsilane (TMS)?

A

the reference standard used in NMR spectroscopy. Its signal is set at δ = 0

41
Q

What is a triplet?

A

a signal in 1H-NMR spectroscopy that has been split into three peaks in a ratio of 1:2:1

42
Q

What does upfield mean?

A

describes a signal in NMR spectroscopy that is towards the right of the spectrum or of another signal

43
Q

What is UV/visible spectroscopy?

A

a technique used to study compounds that absorb light in the ultraviolet-visible region

44
Q

What is vibrational infrared?

A

the portion of the infrared region with a frequency range of 400-4000cm-1

45
Q

What is wavelength (λ)?

A

the distance between any two consecutive identical points on a wave

46
Q

What is wavenumber?

A

the number of wavelengths per centimetre. The unit of wavenumber is the reciprocal centre metre (cm-1) and is commonly used infrared spectroscopy

47
Q

What is X-ray crystallography?

A

the study of crystal structures by X-ray diffraction techniques

48
Q

What spectroscopic technique is used to determine molecular weight of a compound?

A

Mass spectroscopy

49
Q

How many decimal places does High-resolution mass spectroscopy give an accurate reading to?

A

Five decimal placed

50
Q

What spectroscopic technique is used to detect functional groups?

A

Infrared (IR) spectroscopy

51
Q

What determines whether a bond is detectable via IR spectroscopy?

A

It must have a dipole moment

52
Q

What is the most useful spectroscopic technique?

A

Nuclear Magnetic Resonance (NMR) Spectroscopy

53
Q

What does NMR detect?

A

Functional groups
Number of different groups
Connectivity of different groups

54
Q

How do you determine the number of hydrogens in a particular environment?

A

The area under the peak of the NMR graph

55
Q

What is the units used in NMR?

A

Parts per million (not a concentration)

56
Q

What is the chemical shift of Tetramethylsilane (TMS)?

A

0

57
Q

True or false: If a molecule has a plane of symmetry it simplifies the NMR spectrum and we only need to examine one half to determine the NMR spectrum

A

True

58
Q

Do chemically equivalent protons show splitting?

A

No

59
Q

Why does splitting occur in NMR?

A

The protons can be influenced by the magnetic fields of the neighbouring hydrogens.

60
Q

What is the formula for determining the number of protons per hydrogen environment based on NMR data?

A

n + 1 peaks (n = equivalent hydrogens)

61
Q

Where would a band be seen for an alcohol undergoing IR spec?

A

Broad peak around 3000-3500cm-1

62
Q

Where would a band be seen for a molecule with a carbonyl group undergoing IR spec?

A

Strong sharp band around 1700cm-1

63
Q

What is the IHD formula?

A

0.5 x [2c+2-h-x+n]

CHM1022 (13 decks)

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