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forensic chemistry > lecture 2 - Spectroscopy > Flashcards

lecture 2 - Spectroscopy Flashcards

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1
Q

What is spectroscopy?

A

the interaction between light and matter as a function of a wavelength

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2
Q

what is a spectrum?

A

a plot of the response as a function of the wavelength (x-axis = wavenumber & y-axis = absorption)

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3
Q

what is spectrometry?

A

the measurement of these responses

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4
Q

what is infrared spectroscopy?

A

a technique that is used to identify which functional groups are present in a molecule. Functional groups appear at set frequency ranges and these peaks can have characteristic shapes and intensities.

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5
Q

are photons stable or unstable?

A

unstable

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6
Q

what does the electromagnetic spectrum consist of?

A

polychromatic radiation - multiple wavelengths separated into regions

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7
Q

what is the UV electromagnetic spectrum region?

A

190-400nm

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8
Q

what is the visible light region for violet, indigo, blue, green, yellow, and orange

A

violet = 400-420, indigo = 420-440, blue = 440-490, green = 490-570, yellow = 570-585, orange = 585-620

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9
Q

what is absorption spectroscopy?

A

the substance absorbs e.g. infrared

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10
Q

what is emission spectroscopy?

A

the substance radiates e.g. spectrofluorometry

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11
Q

what is scattering spectroscopy?

A

the amount of light a substance scatters e.g. Raman spectroscopy

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12
Q

what is Beer Lamberts law?

A

absorbance is directly proportional to concentration

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13
Q

what is the Beer lamberts formula and what does each letter represent?

A

A=ECL

A = absorbance, E = molar extinction coefficient, C = concentration, L = pathlength

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14
Q

why does absorption occur?

A

as a result of change of vibrational and rotational levels

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15
Q

what does low energy absorption equal?

A

molecular rotations

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16
Q

what does high energy absorption equal?

A

molecular vibrations

17
Q

what does vibrational energy depend on?

A

the arrangement of atoms, masses of atoms, bond distances, and strengths of bonds

18
Q

what is the second beer lamberts law?

A

A = -log I/Io

19
Q

which are stronger bonds; sigma or pie?

A

sigma

20
Q

what is an aliphatic hydrocarbon

A

a hydrocarbon with only single bonds which are very hard to break

21
Q

which type of transition requires the most energy?

A

σ – σ*

22
Q

what does a monochromator do?

A

acts as a filter which turns polychromatic light into monochromatic light

23
Q

what does n – π* and π – π* have in common

A

the presence of unsaturated functional groups

24
Q

what is the fingerprint region in IR spectroscopy

A

the area where the peaks are specific to each molecule = 600-1600cm-1

25
Q

what does IR spectroscopy tell us?

A

molecule composition

26
Q

what is absorption due to in IR spectroscopy

A

stretching or bending

27
Q

what is the definition of stretching in terms of molecular vibrations and what does it cause.

A

vibration or oscillation along the line of the bond - causes the distance between two atoms to increase or decrease but they remain in the same bond axis

28
Q

is stretching asymmetrical or symmetrical

A

both - but IR spec is only asymmetrical because symmetrical does not cause a change in polarity and therefore will not show up in IR spectra

29
Q

in terms of molecular vibrations, what is bending and what does it cause

A

vibration or oscillation not along the line of the bond - it causes the position of atoms to change with respect to the original bond axis

30
Q

what are the 4 types of bending

A

scissoring, rocking, wagging or twisting

31
Q

what is the molecular vibrations formula for linear molecules

A

3n-5, where n is the number of atoms

32
Q

what is the molecular vibrations formula for non-linear molecules

A

3n-6

33
Q

name 4 reasons why the observed vibrations can differ from the predicted number produced from the equation

A

symmetry, energies of vibration are identical, absorption intensity too low, frequencies beyond range of instrument

34
Q

a large U-shaped peak found between 3500-3200 is which functional group

A

the O-H bond of an alcohol

35
Q

a large V-shaped peak found around 3000 is which functional group

A

the O-H bond in carboxylic acids

36
Q

2 peaks found between 3500-3300 and is similar to a W is what functional group

A

a primary amine

37
Q

a short peak found between 3500-3300 and is V-shaped is what functional group?

A

secondary amine

forensic chemistry (7 decks)

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