Infrared Spectroscopy Flashcards Preview

PMP-102 > Infrared Spectroscopy > Flashcards

Flashcards in Infrared Spectroscopy Deck (33)
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1
Q

Infrared Spectroscopy (IR):

A

Measures vibrations of bonds to identify functional groups

2
Q

Ultraviolet Spectroscopy (UV):

A

Measures electronic transitions to provide information on the electronic bonding in the sample

3
Q

Mass Spectrometry (MS):

A

Breaks the molecule into fragments (destructive) and measures the MW of fragments to give information to the structure and functional groups present

4
Q

Nuclear Magnetic Resonance (NMR):

A

Uses electromagnetic fields to measure spinning of nuclei to identify chemical environments leading to identification of functional groups and structure of the sample

5
Q

What is he spectrum called?

A

Electromagnetic Spectrum

6
Q

Electromagnetic Radiations

A

Travel at the speed of light (c) but at different frequencies and wavelengths

7
Q

Frequency (v)

A

= number of complete wave cycles that pass a fixed point per second, Hz (cycles per second)

8
Q

Wavelength (λ) =

A

distance between any two peaks

9
Q

Relationship:

A

λ = c/v, or c = λv, or v = c/ λ

9
Q

Relationship:

A

λ = c/v, or c = λv, or v = c/ λ

10
Q

Photons =

A

massless packs of energy E = hv (h = Planck’s Constant)

11
Q

Molecule struck by a photon:

A

may absorb the photon’s energy and will result in the molecule’s energy increasing by an amount equal to the photon’s energy E = hv

12
Q

Infrared Region

A

Molecular vibrations can be detected in the infrared region.
The covalent bonds between atoms act like springs. If the bond is stretched / compressed and then released, the atoms vibrate

13
Q

Heavier atoms vibrate more ______.
Frequency decreases with __________ atomic mass/

A

slowly
increasing

14
Q

Stronger bonds are more ______ so they vibrate faster.
More ______ needed to stretch / compress (higher frequency)

A

rigid

force

15
Q

What are the three vibrational modes?

A

1 symmetric stretching
2) antisymmetric stretching
3) Bonding (scissoring)

16
Q

Non-linear:

A

Non-linear molecules with n atoms will have 3n – 6 vibrational modes (i.e. 6 atoms = 12 modes)

17
Q

What are the combinations and overtunes of fundamental vibrations called?

A

complex vibrations

18
Q

IR-Active and IR-Inactive vibrations

A

The bond must have a dipole moment.
The vibration must change the dipole moment of the molecule

19
Q

IR-Inactive:
charicteristic

A

Symmetrical / has no dipole moment

20
Q

Infrared Spectroscopy of Hydrocarbons

A

stronger bonds absorb at higher frequencies because of their greater stiffness

21
Q

c-c bond stretching

A
  • isolated
  • conjugated
  • aromatic
22
Q

Different O-H stretching frequencies: important

A

Alcohol (e.g. CH3OH); 3300 cm-1, Broad
Acid (e.g. CH3COOH)l 3300 cm-1, Broad

22
Q

Different O-Hstretching frequesncies:

A

Alcohol (e.g. CH3OH); 3300 cm-1, Broad
Acid (e.g. CH3COOH)l 3300 cm-1, Broad

23
Q

Different C-O frequencies

A

Alcohols and ethers: 1000 – 1200 cm-1

24
Q

N-H Stretching Frequencies

A

Amine: 3300 cm-1 , Broad
1 Spike = N-H of secondary amine (R2NH)
2 Spikes = N-H of primary amine (RNH2)

25
Q

C=O stretching frequencies:

A

Intense absorption at 1700 cm-1
Small overtone peaks at 3400 cm-1
Aldehyde: 1725 cm-1
Ketone: 1710 cm-1

26
Q

C-H stretching frequencies:

A

Aldehyde has two: 2700 and 2800 cm-1

27
Q

Infrared Spectroscopy of Ketones & Aldehydes

A

ketone - 1710cm-1

aldehyde - 1724 / 2700, 2800

28
Q

Strengths and Limitations of IR Spectroscopy

A
  1. Ability to indicate functional groups in the compound
  2. Highlights the absence of other functional groups that would give strong absorptions if they were present
  3. Can confirm identity of a compound by comparison with a known sample
  4. It is non-destructive (sample can be retrieved)
29
Q

what is an overtone in a graph?

A

any resonant frequency above the fundamental frequency
(does not mean anything)

30
Q

revice sprectrum

A

lecture slides - identify absorption location/ intensity of each functional group

31
Q

What is IR:

A

a region of the electromagnetic radiation spectrum where wavelengths range from about 700 nanometers (nm) to 1 millimeter (mm). Infrared waves are longer than those of visible light, but shorter than those of radio waves