NMR Package

Question 1

What does the spin of a Proton create?

Answer 1

A magnetic moment

Question 2

Why does a spinning proton create a magnetic moment?

Answer 2

Because protons carry a positive charge

Question 3

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

Answer 3

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

Question 4

What are the Alpha and Beta spin state?

Answer 4

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

Question 5

Which spin state are most protons in?

Answer 5

An alpha spin state

Question 6

Which spin state of protons has the higher energy level?

Answer 6

Beta spin state

Question 7

What is Resonance?

Answer 7

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

Question 8

What nuclei are responsive to NMR?

Answer 8

Protons and neutrons are both odd

Protons OR neutrons are odd, giving an odd mass number

Question 9

Which nuclei are not Responsive to NMR?

Answer 9

When protons and neutrons are both even

Question 10

What region is the frequency of electromagnetic radiation?

Answer 10

Radio wave frequency

Question 11

What is Shielding?

Answer 11

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

Question 12

What is Deshielding?

Answer 12

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

Question 13

What is the electron density around the proton in Shielding?

Answer 13

Electron density is increased producing a stronger induced magnetic field

Question 14

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

Answer 14

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

Question 15

What is the effect of Shielding on the NMR spectrum?

Answer 15

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

Question 16

What is the electron density around the proton in Deshielding?

Answer 16

Electron density is decreased and a weaker magnetic field is generated

Question 17

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

Answer 17

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

Question 18

What is the effect of Deshielding on the NMR spectrum?

Answer 18

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

Question 19

What is the reference compound in NMR?

Answer 19

Tetramethylsilane (TMS)

Question 20

Why is TMS used as a reference in NMR?

Answer 20

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

Question 21

What is Chemical Shift?

Answer 21

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

Question 22

How does Magnetic Field strength affect NMR?

Answer 22

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

Question 23

What are the characteristics of the ideal NMR solvent?

Answer 23

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

Question 24

What are the 3 important feature of NMR?

Answer 24

The chemical shifts
Peak area
Spin splittings

Question 25

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

Answer 25

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

Question 26

What is the chemical shift like around acetylene?

Answer 26

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

Question 27

What is the chemical shift of H in vinyl?

Answer 27

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

Question 28

What does the position of chemical shift depend on?

Answer 28

The electronegativity of the substituents near the proton | Induced magnetic field of the pi electrons

Question 29

What is the Chemical Shift of protons on aromatic compounds?

Answer 29

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

Question 30

What is the Chemical shift of Aldehydic protons?

Answer 30

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

Question 31

What is the Chemical shift Carboxylic protons?

Answer 31

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

Question 32

What does the area under the peak depict?

Answer 32

The ratio of H's in a compound

Question 33

What is spin spin coupling?

Answer 33

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

Question 34

What is N+1 rule for spin spin coupling?

Answer 34

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

Question 35

When does Complex splitting occur?

Answer 35

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

Question 36

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

Answer 36

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

Question 37

How does D2O determine the presence of hydrogen bonds?

Answer 37

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