Organic Analysis: Infrared Spectroscopy Flashcards

1
Q

What is infrared spectroscopy?

A
  • Analytical technique that identifies the functional groups present in organic compounds
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

How does infrared spectroscopy work?

A
  • It measures wavenumbers (frequencies) of IR radiation beams that pass through a chemical sample
  • (Covalent) bonds in a molecule absorb infrared radiation at characteristic wavenumbers (frequencies)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What factors affect the frequency absorbed by a certain bond?

A
  • The bond enthalpy (strength of bond)

- The masses of atoms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

How does bond enthalpy affect the frequency absorbed by a certain bond?

A
  • Stronger bonds vibrate faster so absorb at higher frequencies
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

How does the masses of atoms affect the frequency absorbed by a certain bond?

A
  • Heavier atoms vibrate more slowly so absorb at lower frequencies
  • E.g heavier guitar string = lower frequency
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Name different types of bond vibrations

A
  • Bending
  • Stretching
  • Symmetric stretching
  • Asymmetric stretch
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Explain how radiation affects bond vibrations

A
  • IR radiation is absorbed by covalent bonds increasing their vibrational energy
  • Different covalent bonds have different strengths due to masses of different atoms at either end of bond
  • So, bonds vibrate at different frequencies
  • There are different types of bond vibrations
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does an infrared spectrometer look like?

A
  • Wavenumber on x-axis; transmittance on y-axis
  • Shows what frequencies of radiation the bond in molecules are absorbing
  • The peaks show you where radiation is being absorbed
  • The peaks are upside down
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How do you interpret an infrared spectrometer?

A
  • Look at wavenumber of a particular peak

- Look at data sheet and identify group that includes the peak’s wavenumber

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Why are some peaks broader than others?

A
  • Some organic compounds form hydrogen bonds between molecules which makes peak broader
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is the fingerprint region?

A
  • Region between 1500-400cm^-1 is known as ‘fingerprint’ region
  • Each compound has a unique fingerprint region
  • Compound can be identified by comparing spectrum with sample spectra stored in a database
  • Spectrum - the entire range of wavelengths of electromagnetic radiation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How do greenhouse gases contribute to global warming?

A
  • The Sun emits UV radiation which is absorbed by the Earth’s surface and re-emitted as IR radiation
  • Molecules of greenhouse gases have bonds that are good at absorbing infrared energy
  • If amount of greenhouse gases in atmosphere increase, more IR radiation is absorbed leading to global warming
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Name examples of greenhouse gases

A
  • Carbon dioxide
  • Methane
  • Water vapour
How well did you know this?
1
Not at all
2
3
4
5
Perfectly