Chapter 14

0.0(0)
learnLearn
examPractice Test
spaced repetitionSpaced Repetition
heart puzzleMatch
flashcardsFlashcards
Card Sorting

1/59

flashcard set

Earn XP

Description and Tags

Infrared Spectrometry

Study Analytics
Name
Mastery
Learn
Test
Matching
Spaced

No study sessions yet.

60 Terms

1
New cards

Why do we need to be able to determine the structure of unknown compounds in organic chemistry?

To determine what lab reaction will occur as the outcome and to discover new compounds.

2
New cards

What is spectrometry?

The measure of mass

3
New cards

What is spectroscopy?

The study of the absorption of energy.

4
New cards

What does nulcear magneti resonance or NMR tell use?

The arrangement of specific atoms in a molecule.

5
New cards

What does 13C NMR tell us?

THe carbon skeleton

6
New cards

What does 1H NMR tell us?

The proton arrangement of an atom

7
New cards

What is the theory behind NMR?

Radio waves make nuclei resonate

8
New cards

What does Infrared spectroscopy (IR) tell us?

The functional groups present in a molecule.

i.e. C=C or C=O

9
New cards

What is the theory behind IR?

Infrared radiation makes bonds vibrate. The bond acts a a spring in the molecule with more or less energy depending on the molecule.

10
New cards

What does mass spectrometry (MS) tell us?

The molecular mass and structure of a molecule, allowing us to determine molecular formula and isotopes.

11
New cards

What is the theory behind MS?

Mass detection of ions; ionization by bombarding with electrons, chemicals, etc.

12
New cards

What is quantization?

The energy level at which a bond can vibrate.

13
New cards

Energy of a bond depends on the nature of the bond. What determines the nature of a bond?

Bond strength and Atomic MassThe types of atoms involved and their electronegativities.

14
New cards

When looking at an infrared spectrum of a molecule the y axis is marked as transistance. What is this?

How much light is transmitted though a sample. (A Percentage)

15
New cards

What is defined as the diagnostic region?

The range of wavelengths in an infrared spectrum that provides information about functional groups in a molecule. (Double bonds, Triple bonds, bonds to H, etc.) Occurs above 1500cm-1

<p>The range of wavelengths in an infrared spectrum that provides information about functional groups in a molecule. (Double bonds, Triple bonds, bonds to H, etc.) Occurs above 1500cm<sup>-1</sup></p>
16
New cards

What is defined as the fingerprint region of an Infrared Spectrum?

The region of a spectrum that denotes single bonds such as C-C or C-O. Occurs below 1500 cm-1

<p>The region of a spectrum that denotes single bonds such as C-C or C-O. Occurs below 1500 cm<sup>-1</sup></p>
17
New cards
<p>What does a dip (signal) denote in an infrared spectrum?</p>

What does a dip (signal) denote in an infrared spectrum?

A specific type of bond located in the molecule.

<p>A specific type of bond located in the molecule. </p>
18
New cards

The wave number (ṽ) is proportional to what?

1 / 𝜆

19
New cards

What is bond energy proportional to?

Wavenumber or 1 / 𝝀

20
New cards

As atomic mass increases, …

Wavenumber decreases

21
New cards

As bondstrength increases, …

Wavenumber increases

22
New cards

What is the formula for wavenumber?

.

<p>.</p>
23
New cards

As polarity increases, …

The intensity of a signal increases

24
New cards

As hydrogen bonding increases, …

The shape of the signal becomes broader

25
New cards

If overlapping peaks occur in an infrared spectrum that makes a portion of the graph appear broad what atom is likely involved?

carbon

<p>carbon</p>
26
New cards

The effect of resonance is conjugation. What is Conjugation and what does it cause?>

The existence of alternating pi bonds (π-∂-π). This reduces the wavenumber by 30 points.

<p>The existence of alternating pi bonds (π-∂-π). This reduces the wavenumber by 30 points. </p>
27
New cards

How doe we report information obtained from an IR spectrum?

Using the table to determine what functional groups are present and writing the observations in a clear format.

Report Wavenumber, Intensity, Shape, and Bond Stretch in that order with no decimals

i.e. 1735 cm-1 (strong, C=O of ester)

28
New cards

What can happen to the alcohol dip on an IR spectrum if in a dilute solution?

The dip can anrrow.

29
New cards

If a terminal alkyne is present where in the chart must you look after identifying the terminal alkyne?

The triple bond region around 2100-2260 cm-1

30
New cards

What value is C sp2 found above and C sp3?

3000 cm-1

31
New cards

Why does an aldehyde give two weak signals on an IR Spectrum?

Overtones due to Ferni resonance.

32
New cards

How do you distinquish an aldehyde from a ketone in an IR spectrum since the wave number for the carbonyl are nearly identical?

You must look for the C-H bond in an aldehyde, which is prsent in the region around 2720-2820 cm-1, indicating the presence of the aldehyde functional group.

33
New cards
<p>When identifying a Carboxylic acid what also must be account for and recorded other than the extremely wide dip?</p>

When identifying a Carboxylic acid what also must be account for and recorded other than the extremely wide dip?

An O-H bond

34
New cards

When recognizing an amide by the carbonyl group what also must be accounted for?

The N-H bond

35
New cards

What are the only fingerprint region C-O bonds to focus on?

Ester, Ether, and Alcohol Bonds

<p>Ester, Ether, and Alcohol Bonds</p>
36
New cards

What does mass spectrometry do?

It detects exact mass of charged species

37
New cards

What does periodic table show in terms of atomic mass?

The average atomic mass of all kinds of isotopes.

38
New cards

What is the ratio of Chlorine isotopes?

The ratio of Chlorine isotopes is approximately 3:1, with about 75% being chlorine-35 and 25% chlorine-37.

39
New cards

What is the ratio of Bromine isotopes?

The ratio of Bromine isotopes is approximately 1:1, with about 50% being bromine-79 and 50% bromine-81.

40
New cards

What can mass spectrometry only detect?

Ions

41
New cards

What is the first step of mass spectrometry?

Inject and vaporize

Separate compounds using coupled instruments like GC-MS (Gas chromatography) and LC-MS (Liquid chromatography)

42
New cards

What is the second step of mass spectrometry?

Ionize the compound to create charged particles for analysis. Through either Electron-impact (EI) or Electrospray (ESI).

43
New cards

What is the result of ionization with electron impact (EI)?

It is a hard reaction that results in fragmentation.

44
New cards

What is the result of ionization with Electrospray (ESI)?

It is a softer reaction that is better for biomolecules such as proteins.

45
New cards

What is step three of mass spectrometry?

Separating ions using a mass analyzer that accelerates and deflects ions.

46
New cards

What is step four of mass spectrometry?

Detect the ions as a mass to charge ratio (m/z), If seen as a charge of +1 the ratio is the actual mass. This step involves measuring the abundance of ions at different m/z values to create a mass spectrum that represents the sample's composition.

47
New cards

In a mass spectrometry experiment was is detected?

The exact mass not the molecular weight.

48
New cards

What is the base peak in mass spectrometry?

The most intense peak in a mass spectrum, representing the most abundant ion.

49
New cards

What is the molecular ion peak in a mass spectrometry?

The peak that corresponds to the ions of the original molecule, indicating its molecular weight. It is typically the highest m/z value in the spectrum that reflects the intact molecule. Denoted as [M]+

50
New cards

A secondary peak that is a molecular ion peak denotes an isotope of the atom in question that is in lower abundance. How is it denotes?

[M+1]+

51
New cards

WHat is the fragment that you can view at the 77 mau point?

phenol group

52
New cards

What is the nitrogen rule of mass spectrometry?

A guideline stating that compounds with an odd number of nitrogen atoms have an odd molecular ion, while those with an even number have an even molecular ion. This rule helps in predicting the molecular formula based on the mass spectrum.

53
New cards

How do you determine the molecular formula of a compound continuing heteroatoms with mass spectrometry?

You have to look to IR or NMR.

54
New cards

What is the Hydrogen Definciecy Index state?

It is a measure of the degree of unsaturation in a compound, calculated as the difference between the number of hydrogen atoms in a fully saturated compound and the actual number of hydrogen atoms present. It helps in deducing the structure of organic compounds by telling you the number of π bonds and/or rings in a compound.

55
New cards

WHat does a Zero DUs mean?

The compound is saturated and there are no rings or π bonds.

56
New cards

How do yoou calculat eht number of carbon atoms in a molecule?

.

<p>. </p>
57
New cards

How do you determine the number of hydrogens in a molecular formula using mass spectrometry?

.

<p>. </p>
58
New cards

How do you determine if a molecular formula is resonable?

By using teh DU and spectral data

59
New cards

If the peak of the molecule is found to be [M-H2O]+ what do you do to get [M]+

Add H2O

60
New cards

How do we differentiate between a primary and secondary amine on IR?

By looking for bumps in the signal. 2 bumps means a primary amine and 1 bump means a secondary amine

<p>By looking for bumps in the signal. 2 bumps means a primary amine and 1 bump means a secondary amine</p>