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Ochem II > NMR Package > Flashcards

NMR Package Flashcards

1
Q

What does the spin of a Proton create?

A

A magnetic moment

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2
Q

Why does a spinning proton create a magnetic moment?

A

Because protons carry a positive charge

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3
Q

What happens to a proton in the presence of an external magnetic field?

A

Two orientations become possible for the proton. An alpha or beta spin state

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4
Q

What are the Alpha and Beta spin state?

A

An alpha spin state is when a protons magnetic field is aligned with the external magnetic field. A beta spin state is when a protons magnetic field is against an external magnetic field

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5
Q

Which spin state are most protons in?

A

An alpha spin state

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6
Q

Which spin state of protons has the higher energy level?

A

Beta spin state

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7
Q

What is Resonance?

A

The energy needed to flip an alpha spin state to a beta spin state

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8
Q

What nuclei are responsive to NMR?

A

Protons and neutrons are both odd

Protons OR neutrons are odd, giving an odd mass number

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9
Q

Which nuclei are not Responsive to NMR?

A

When protons and neutrons are both even

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10
Q

What region is the frequency of electromagnetic radiation?

A

Radio wave frequency

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11
Q

What is Shielding?

A

When the surrounding electrons shield the nucleus so that the effective magnetic field felt by the nucleus is lower than the applied field. Because the electrons create a field that oppose the applied field

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12
Q

What is Deshielding?

A

When the induced field can reinforce the applied magnetic field because the electron density around nucleus is decreased

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13
Q

What is the electron density around the proton in Shielding?

A

Electron density is increased producing a stronger induced magnetic field

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14
Q

What is the Magnetic field like around the proton in Shielding?

A

Proton experiences less external magnetic field and a stronger magnetic field is needed for resonance

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15
Q

What is the effect of Shielding on the NMR spectrum?

A

Signal goes upfield (to the right of the NMR spectrum)

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16
Q

What is the electron density around the proton in Deshielding?

A

Electron density is decreased and a weaker magnetic field is generated

17
Q

What is the Magnetic field like around the proton in Deshielding?

A

A proton experiences a stronger magnetic field (A weaker magnetic field is needed for resonance)

18
Q

What is the effect of Deshielding on the NMR spectrum?

A

The signal goes downfield (to the left of the NMR spectrum)

19
Q

What is the reference compound in NMR?

A

Tetramethylsilane (TMS)

20
Q

Why is TMS used as a reference in NMR?

A

All the methyl groups are equivalent giving a single peak
It is soluble in most organic solvents
It absorbs at the highest field

21
Q

What is Chemical Shift?

A

The difference in absorption of a particular priority from the absorption position of the reference proton

22
Q

How does Magnetic Field strength affect NMR?

A

The stronger the magnetic field, the broader the NMR scale and a better resolution

23
Q

What are the characteristics of the ideal NMR solvent?

A

Must not have any protons so as not to produce peaks
Low boiling point
Inert

24
Q

What are the 3 important feature of NMR?

A

The chemical shifts
Peak area
Spin splittings

25
Q

How does increased electronegativity of an element affect the H NMR?

A

Increased electronegativity of nearby elements pulls electrons from the H increasing the deshielding effect causing the signal to move downfield

26
Q

What is the chemical shift like around acetylene?

A

The protons are strongly shielded by the pi electrons and therefore move upfield

27
Q

What is the chemical shift of H in vinyl?

A

The chemical shift is higher because the protons are deshielded by the induced field of pi electrons

28
Q

What does the position of chemical shift depend on?

A

The electronegativity of the substituents near the proton

Induced magnetic field of the pi electrons

29
Q

What is the Chemical Shift of protons on aromatic compounds?

A

Aromatic protons are deshielded by the induced ring current causing the signal to move downfield. Around 7.27

30
Q

What is the Chemical shift of Aldehydic protons?

A

They are strongly deshielded by the magnetic field of the double bond and the electronegativity of the oxygen. Around 10

31
Q

What is the Chemical shift Carboxylic protons?

A

Because they are strongly desheilded by the double bond and the oxygen it is around 10-12

32
Q

What does the area under the peak depict?

A

The ratio of H’s in a compound

33
Q

What is spin spin coupling?

A

When instead of showing up as single peaks, thay appear as multiplets in NMR because the coupling effect of protons. Adjacent protons affect protons nearby

34
Q

What is N+1 rule for spin spin coupling?

A

The nearby protons that are not identical to the +1 determines the amount of peaks that a proton will have

35
Q

When does Complex splitting occur?

A

Complex splitting occurs when the neighboring protons do not have all the same signal

36
Q

What is different about -OH and -NH in NMR?

A

Due to hydrogen bonding, their position on NMR depends on concentration. Concentrated solutions move downfield due to hydrogen bonding that increases Deshielding

37
Q

How does D2O determine the presence of hydrogen bonds?

A

If D2O is shaken with a compound with hydrogen bonds, the signal will disappear because it will undergo a proton exchange

Ochem II (1 decks)

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