Unit 4 structural deteremination Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

In fragmentation in mass spectrometry, a molecular ion breaks up into fragments. What does each fragment carry and which one will be detected?

A

One fragment will carry a positive charge and the other will carry an unpaired electron. The fragment with a positive charge will be detected.

M+•→X+ + Y

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

What is the peak furthest to the right in a mass spectrum called? What does it tell you about the molecule?

A

The molecular ion peak, it tells you the Mr of the molecular ion.

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

What is the region called below 1500cm-1 in Infra-red spectroscopy? How is it useful in determining the structure of a substance?

A

It is called the fingerprint region. It is unique for any particular substance, so it can be used to indentify a substance by comparing its infra-red spectrum to a known sample’s.

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

What infra-red spectrum peaks would be expected for ethyl ethanoate?

A

1 peak between 1680-1750cm-1 for a C=O bond, and 2 peaks between 1000-1300cm-1 for 2 C-O bonds.

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

What is the name of the compound used to indicate 0 ppm in 13C and proton nmr? What is its structure?

A

Tetramethylsilane (TMS)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Ethanol has 2 peaks in a 13C nmr spectra, one between 5-40 ppm for a C-C bond and one between 50-90 ppm for a C-O bond, why does the carbon bonded to an oxygen have a higher chemical shift than the other carbon?

A

The oxygen draws electrons away from the carbon bonded to it, meaning the carbon is less shielded so it feels a greater magnetic field and resonates at a greater frequency and has a greater chemical shift value than the other carbon.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What does the integration trace tell you about a proton (1H) nmr spectra?

A

It tells you the ratio of hydrogens represented by each peak.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

In proton (1H) nmr spectra, peaks are usually split into multiple smaller peaks. What does the number of peaks tell you about a hydrogen?

A

The number of peaks minus 1 tells you the number of hydrogens on carbon atoms adjacent to the hydrogen the peak is for.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What would the proton (1H) nmr spectra of propanoic look like?

A

The ratio of hydrogens will be 3:2:1 which can be found by integration.

The first peak has 3 hydrogens due to its ratio and will have 2 hydrogens on adjacent carbons as it is split into 3 peaks.

The second peak has 2 hydrogens due to its ratio and will have 3 hydrogens on adjacent carbons as it is split into 4 peaks.

The third peak won’t be split and will be between 10-12 ppm which represents the OH hydrogen. It will be a singlet as it has no hydrogens on its adjacent carbon.

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