lecture 2 - Spectroscopy

Question 1

What is spectroscopy?

Answer 1

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

Question 2

what is a spectrum?

Answer 2

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

Question 3

what is spectrometry?

Answer 3

the measurement of these responses

Question 4

what is infrared spectroscopy?

Answer 4

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.

Question 5

are photons stable or unstable?

Answer 5

unstable

Question 6

what does the electromagnetic spectrum consist of?

Answer 6

polychromatic radiation - multiple wavelengths separated into regions

Question 7

what is the UV electromagnetic spectrum region?

Answer 7

190-400nm

Question 8

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

Answer 8

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

Question 9

what is absorption spectroscopy?

Answer 9

the substance absorbs e.g. infrared

Question 10

what is emission spectroscopy?

Answer 10

the substance radiates e.g. spectrofluorometry

Question 11

what is scattering spectroscopy?

Answer 11

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

Question 12

what is Beer Lamberts law?

Answer 12

absorbance is directly proportional to concentration

Question 13

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

Answer 13

A=ECL

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

Question 14

why does absorption occur?

Answer 14

as a result of change of vibrational and rotational levels

Question 15

what does low energy absorption equal?

Answer 15

molecular rotations

Question 16

what does high energy absorption equal?

Answer 16

molecular vibrations

Question 17

what does vibrational energy depend on?

Answer 17

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

Question 18

what is the second beer lamberts law?

Answer 18

A = -log I/Io

Question 19

which are stronger bonds; sigma or pie?

Answer 19

sigma

Question 20

what is an aliphatic hydrocarbon

Answer 20

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

Question 21

which type of transition requires the most energy?

Answer 21

σ – σ*

Question 22

what does a monochromator do?

Answer 22

acts as a filter which turns polychromatic light into monochromatic light

Question 23

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

Answer 23

the presence of unsaturated functional groups

Question 24

what is the fingerprint region in IR spectroscopy

Answer 24

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

Question 25

what does IR spectroscopy tell us?

Answer 25

molecule composition

Question 26

what is absorption due to in IR spectroscopy

Answer 26

stretching or bending

Question 27

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

Answer 27

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

Question 28

is stretching asymmetrical or symmetrical

Answer 28

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

Question 29

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

Answer 29

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

Question 30

what are the 4 types of bending

Answer 30

scissoring, rocking, wagging or twisting

Question 31

what is the molecular vibrations formula for linear molecules

Answer 31

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

Question 32

what is the molecular vibrations formula for non-linear molecules

Answer 32

3n-6

Question 33

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

Answer 33

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

Question 34

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

Answer 34

the O-H bond of an alcohol

Question 35

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

Answer 35

the O-H bond in carboxylic acids

Question 36

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

Answer 36

a primary amine

Question 37

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

Answer 37

secondary amine

Question 38

how many IR vibrations does carbon dioxide have and what are they called

Answer 38

4 symmetrical stretch, asymmetrical stretch, horizontal bending and vertical bending