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AA - Organic Chemistry 2 - Chamberland > Ch. 12 - Infrared Spectroscopy > Flashcards

Ch. 12 - Infrared Spectroscopy Flashcards

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1
Q

Gamma rays, X-rays, ultraviolet light, visible light, infrared radiation, microwaves, and radio waves are all types of ______?

A

Electromagnetic radiation

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2
Q

Define wavelength

A

The distance between consecutive peaks on a wave

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3
Q

Define frequency

A

The number of full cycles of a wave that pass a given point in a second; it is given the symbol v (Greek nu) and reported in hertz (Hz), which has the units s-1.

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4
Q

What unit is frequency measured in?

A

Hertz

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5
Q

True or False:

wavelengths and frequency are inversely proportional

A

True

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6
Q

Define: Molecular Spectroscopy

A
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7
Q

Define: Infrared (IR) spectroscopy

A

A spectroscopic technique in which a compound is irradiated with infrared radiation, absorption of which causes covalent bonds to change from a lower vibration state to a higher one. Infrared spectroscopy is particularly valuable for determining the kinds of functional groups present in a molecule.

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8
Q

At what wavelength range is Infrared spectroscopy dependent?

A

2.5 x 10-6 to 2.5 x 10-5 m

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9
Q

2.5 x 10-6 to 2.5 x 10-5​ Is also known as?

A

Vibrational infrared region

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10
Q

Define: wavenumbers

A

The frequency of electromagnetic radiation expressed as the number of waves per centimeter, with units cm-1 (read: reciprocal centimeters).

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11
Q

In frequencies, what is the vibrational infrared region?

A

4000 to 400 cm-1

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12
Q

Why are NaCl and KBr often used in sample preparation for spectroscopy?

A

As ionic solids, they have no covalent bonds to absorb infrared radiation.

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13
Q

True or false:

In general, the greater the bond dipole, the greater change in dipole moment caused by a vibration.

A

True

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14
Q

Define: Infrared active

A

Any molecular vibration that leads to a substantial change in dipole moment is observed in an IR spectrum

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15
Q

Are these molecules infrared active or inactive?

A

Infrared inactive. This is because the carbon-carbon double and triple bonds of symmetrically substituted alkanes and alkanes do not absorb infrared radiation because vibration does not result in substantial bond dipole change.

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16
Q

What is the formula for allowed fundamental vibrations of a nonlinear molecule containing n atoms?

A

3n - 6

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17
Q

What is the formula for allowed fundamental vibrations of a linear molecule containing n atoms?

A

3n - 5

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18
Q

Define: Raman spectroscopy

A
19
Q

What is the equation, derived from Hooke’s law for a vibrating spring, for the frequency of a stretching vibration? And what does each variable mean?

A
20
Q

True or False:

Frequencies calculated using the equation for the frequency of a stretching vibration is generally precise enough to determine molecular structure

A

False

21
Q

True or false:

The stronger the bond is and the lighter the atoms are, the higher the frequency of the stretching vibration will be.

A

True.

Hooke’s law depends on both the strength of the vibrating bond and the masses of the atoms connected by the bond.

22
Q

Without doing a calculation, which of this pair will occur at the higher frequency?

A

Although O has a larger mass, the carbon-oxygen bond is much stronger than the carbon-carbon bond.

23
Q

Without doing the calculation, which of this pair will occur at the higher frequency?

A

The triple bond is much stronger than the double bond, causing it to occur at a higher frequency regardless of the carbon-oxygen double bond.

24
Q

Without doing the calculation, which of this pair will occur at the higher frequency?

A

Assuming the single bonds are similar in force constants, the hydrogen being so small in mass would result in a higher frequency when put into the equation.

25
Q

What is the stretching frequency of an O–H bond? Is it classified as weak, strong, or medium?

A

3200 - 3650 cm-1

Weak to strong

26
Q

What is stretching frequency of an N–H bond? Intensity?

A

3100 - 3550

Medium

27
Q

What is the stretching frequency of a C–H bond? Intensity?

A

2700 - 3300

Weak to Medium

28
Q

What is the stretching frequency of a Carbon-Carbon double bond? Intensity?

A

1600 - 1680

Weak to Medium

29
Q

What is the stretching frequency of a Carbon-Oxygen double bond? Intensity?

A

1630 - 1820

Strong

30
Q

What is the stretching frequency of a C–O? Intensity?

A

1000 - 1250

Strong

31
Q

What is the fingerprint region?

A
32
Q

True or False:

Infrared spectra of alkanes are usually complex with many peaks.

A

False.

Infrared spectra of alkanes are usually simple with few peaks.

33
Q

What are the 4 major infrared absorptions of alkanes?

Include:

  • hydrocarbon
  • vibration type
  • frequency
  • intensity
A
34
Q

What are the 2 major infrared absorptions of alkenes?

Include:

  • hydrocarbon
  • vibration type
  • frequency
  • intensity
A
35
Q

What are the 2 major infrared absorptions of alkynes?

Include:

  • hydrocarbon
  • vibration type
  • frequency
  • intensity
A
36
Q

What are the 3 major infrared absorptions of arenes?

Include:

  • hydrocarbon
  • vibration type
  • frequency
  • intensity
A
37
Q

What are the 3 major infrared absorptions of alcohols?

include:

  • bond
  • frequency
  • intensity
A
38
Q

How many bands can be seen in primary amines and secondary amines?

A

Primary amines show 2 bands due to one being caused by symmetric stretching and the other by asymmetric stretching.

Secondary amines show 1 band of absorption in the same region as primary.

Tertiary amines show no bands as there are no N-H bonds

39
Q

What frequency do aldehydes and ketones fall under in infrared spectroscopy?

A

Between 1630 and 1820 cm-1

40
Q

True or False:

As ring size decreases and angle strain increases, the Carbon-Oxygen double bond absorption shifts to a higher frequency

A

True

41
Q

What occurs when a carbonyl group has the presence of an adjacent carbon-carbon double bond or benzene ring?

A

The Carbon-Oxygen double bond shifts to a lower frequency.

42
Q

If you were shown an IR spectrum showing a peak at 1700-1725 cm-1 and another at 2500-3300 cm-1, what is likely the molecule you are observing?

A

It is likely a Carboxylic Acid.

*Carboxylic acids show two peaks. One from the carbonyl at 1700-1725 cm-1 and another due to the O-H bond at 2500-3300 cm-1

43
Q

Describe the systematic approach to solving IR problems

A
44
Q
A

AA - Organic Chemistry 2 - Chamberland (2 decks)

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