Spectroscopy

Question 1

Spectroscopy

Answer 1

Measures the energy differences between the possible states of a molecular system by determining the frequencies of electromagnetic radiation absorbed by molecules

Question 2

Infrared spectroscopy

Answer 2

Measures molecular vibrations, which can be seen as bond stretching or bending
Infrared light passed through sample and absorbance is measured

Question 3

Wavenumber

Answer 3

4000 to 400 cm^-1

Question 4

What wavelengths do spectroscopy occur?

Answer 4

2500 to 25,000 nm

Question 5

Wavenumber equation

Answer 5

1/wavelength

Question 6

Fingerprint region

Answer 6

Above 1500 cm^-1

More complex vibration patterns

Question 7

What kind of molecules would not exhibit absorption?

Answer 7

Ones that don’t experience a change in dople

Same electronegativity or symmetrical molecules

Question 8

Hydroxyl group absorption

Answer 8

Broad OH at 3300 for alcohol

At 3000 for carboxylic acid

Question 9

Larger wavelength corresponds to what wavenumber?

Answer 9

Smaller

Question 10

Smaller wavelength corresponds to what wavenumber?

Answer 10

Larger

Question 11

Carbonyl group absorption

Answer 11

1700 cm^-1 deep

Question 12

DIfference between NH and OH group

Answer 12

NH still at 3300, but sharper peak

Question 13

Which has a higher wavenumber, bound to alkyne or alkane

Answer 13

Alkyne

Question 14

Percent transmittance

Answer 14

Amount of light passed through the sample and reaches detector

Question 15

Absorbance and percent transmittance equation

Answer 15

A=2-log%T

More absorbance with less transmittance

Question 16

UV Spectroscopy

Answer 16

Passing UV light through a sample that is usually dissolved in inert, nonabsorbing solvent, and reading absorbance plotted against wavelength
Tells extent of max absorbance that tells extent of conjugation

Question 17

More conjugated compounds have what kind of UV spec

Answer 17

Lower energy of transition and greater wavelength of max absorbance

Question 18

What is UV spec most useful for studying

Answer 18

Compounds with double bonds or heteroatoms with lps that make conjugated systems

Question 19

UV spec excites what kind of electrons

Answer 19

pi electrons or non-bonding electrons

Question 20

What kind of molecules are more easily excited with UV light

Answer 20

Smaller energy gap between (HOMO) highest occupied molecular orbital and (LUMO) lowest unoccupied molecular orbitals

Question 21

Conjugated molecules

Answer 21

Unhybridized p-orbitals can also be excited by UV light

Conjugation shifts absorption to higher max wavelength and lower frequencies

Question 22

NMR Spec

Answer 22

Certain atomic nuclei have magnetic moments oriented at random, in magnetic fields the magnetic moment aligns with or against field

Question 23

a-state

Answer 23

Magnetic moments aligned with field (lower energy)

Question 24

B-state

Answer 24

Higher energy state when nuclei are irradiated with radiofrequency pulses that match the energy gap between two states and excitation at different frequencies

Question 25

MRI

Answer 25

Uses proton NMR to translate into shades of grey (water), lighter (tissue)

Question 26

Plot of NMR axes

Answer 26

Frequency v. absorption energy

Question 27

Chemical shift

Answer 27

Uses parts per million (ppm) of spectrometer frequency

Question 28

What way does frequency increase on the x-axis

Answer 28

To the left (downfield0

Question 29

What is used at 0 ppm to calibrate NMR?

Answer 29

TMS tetramethysilane

Question 30

More electronegative elements attached to a carbon causes the hydrogen to shift?

Answer 30

Downfield

Question 31

Integration

Answer 31

Ratio of peaks corresponds to ratio of protons produced each peak

Question 32

Deshielding

Answer 32

Pulling electron density away from surrounding atoms, less it can protect itself from magnetic field and is absorbed at a higher frequency

Question 33

Shielding

Answer 33

Electron donating groups shift it upfield

Question 34

Splitting

Answer 34

Within three bonds of each other,

Question 35

n +1 rule

Answer 35

If a proton has n protons that are n bonds away, it will be split into n + 1 peaks except ones attached to O or N

Question 36

Coupling constant J

Answer 36

Magnitude of splitting (in Hertz)

Question 37

Multiplet

Answer 37

Greater than 4 shifts

Question 38

Aldehyde ppm

Answer 38

9-10 ppm

Question 39

Carboxylic acid ppm

Answer 39

10.5- 12 ppm

Question 40

Aromatic ring

Answer 40

6-8.5 ppm

Question 41

Which kind of bond is further down field?

Answer 41

Sp^2, sp, sp^3

Question 42

Extended conjugation of double bonds causes stretches where compared to normal absorption?

Answer 42

Occuring at lower wavenumber

Question 43

Wavenumber is directly proportional to?

Answer 43

Frequency bc frequency = c/wavelength

Question 44

Why can't carbon 12 be used for NMR

Answer 44

It has no magnetic moment bc it has an even mass number