Spectroscopy

Question 1

What does IR spectroscopy stand for?

Answer 1

Infrared

Question 2

What does IR spectroscopy measure?

Answer 2

Molecular vibrations - bending and stretching bonds

Question 3

What wavelengths do IR spectroscopy measure?

Answer 3

700nm to 1mm

Question 4

What is wavenumber and what units is it measured in?

Answer 4

1/wavelength, cm-1

Question 5

What is the relationship between wavenumber and frequency?

Answer 5

Directly proportional

Question 6

What wavenumbers do IR spectroscopy measure?

Answer 6

4000-400cm-1

Question 7

Does symmetric stretch show up on IR spectroscopy and why?

Answer 7

No because there is no net change in dipole

Question 8

Does asymmetric stretch show up on IRB spectroscopy and why?

Answer 8

Yes because there is a change in net dipole

Question 9

What wavenumbers characterize the fingerprint region?

Answer 9

1500-400cm-1

Question 10

What is the fingerprint region?

Answer 10

Specific absorbance pattern characteristic to each molecule

Question 11

What is the frequency and shape of the -OH peak in alcohol?

Answer 11

Wide (broad) peak at 3300

Question 12

What is the frequency and shape of the -OH peak in carboxylic acid?

Answer 12

Wide (broad) peak at 3000

Question 13

What is the frequency and shape of the C=O peak?

Answer 13

Sharp peak at 1700

Question 14

What is the frequency and shape of the -NH peak?

Answer 14

Sharp peak at 3300

Question 15

What peak is broad at 3300?

Answer 15

Alcohol OH

Question 16

What peak is broad at 3000?

Answer 16

Carboxylic Acid OH

Question 17

What is the carboxylic acid OH lower than alcohol OH peak?

Answer 17

Carbonyl draws some electron density in carboxylic acid

Question 18

What peak is sharp at 1700?

Answer 18

Carbonyl

Question 19

What peak is sharp at 3000?

Answer 19

N-H

Question 20

Do higher order bonds have higher or lower absorption frequencies?

Answer 20

Higher

Question 21

What is plotted in IR Spectroscopy?

Answer 21

Wavenumber on x and %transmittance on y

Question 22

What does UV spectroscopy stand for?

Answer 22

Ultraviolet

Question 23

What does UV spectroscopy measure?

Answer 23

Absorbance of a sample dissolved in inert solution when UV light is passed through it

Question 24

What is plotted in UV spectroscopy?

Answer 24

Absorbance vs wavelength

Question 25

What causes absorbance of UV light?

Answer 25

Electronic transitions between orbitals

Question 26

Does conjugations increase or decrease the wavelength of maximum absorbance and why?

Answer 26

Increase due to lower energy of transition due to lower energy gap between HOMO and LUMO

Question 27

HOMO

Answer 27

Highest occupied molecular orbital

Question 28

LUMO

Answer 28

Lowest unoccupied molecular orbital

Question 29

What is the relationship between wavelength and frequency?

Answer 29

Inversely proportional

Question 30

What is the units for chemical shift?

Answer 30

Parts per million (ppm)

Question 31

Chemical shift of 0

Answer 31

TMS reference line

Question 32

Which way does a downfield shift move?

Answer 32

Left

Question 33

Which way does an upfield shift move?

Answer 33

Right

Question 34

What does the height of a peak in NMR spec represent?

Answer 34

Proportional to the number of protons

Question 35

How do electronegative atoms affect chemical shift and why?

Answer 35

Deshield protons by drawing away electron density and move the peak downfield

Question 36

Which direction does deshielding move the peak?

Answer 36

Downfield, left

Question 37

Deshielding

Answer 37

Electronegative atoms draw electron density from the proton and move the chemical shift downfield, left

Question 38

Spin-spin coupling

Answer 38

Two protons that are not magnetically identical within three bonds of one another

Question 39

How many peaks are present in spin-spin coupling?

Answer 39

n+1 where n is the number of protons less than 3 bonds away from the proton of interest

Question 40

What is the chemical shift of an aldehyde proton?

Answer 40

9-10ppm

Question 41

What is the chemical shift of a carboxylic acid proton?

Answer 41

10.5-12ppm

Question 42

What is the chemical shift of a benzene proton?

Answer 42

6-8.5