NMR Video

Question 1

What are the 3 components of NMR?

Answer 1

Chemical Shift, Integration, and J-coupling

Question 2

What is the entire concept of NMR based on?

Answer 2

Each nucleus has a specific spin. When you apply a magnetic field to the nucleus, it can either be aligned with or against the field. Essentially, a radio frequency pulse is applied and the nuclei absorb the energy. When talking about NMR, we’re dealing with hydrogens.

Question 3

Define Chemical Shift

Answer 3

Different protons absorb at different frequencies; it’s a measure of the magnetic field the hydrogens experience.

Question 4

When the value of a chemical shift is 0, what do we call it?

Answer 4

Low Shift/Upfield/Shieded

Question 5

When the value of a chemical shift is high, what do we call it?

Answer 5

High Shift/Downfield/Deshielded

Question 6

What is the relationship between the frequency of light absorbed by hydrogens and the amount of magnetic field that they experience?

Answer 6

Direct; it’s proportional.

Question 7

What do the terms “shielded’ and “deshielded” refer to respectively?

Answer 7

The amount of electron density surrounding the hydrogens; shielded means that there is a high electron density and deshielded means that there’s a low electron density.

Question 8

What does Integration cover?

Answer 8

The amount of hydrogens are measured by measuring the area under each peak.

Question 9

How can the area under each peak be determined if numerical values are not provided?

Answer 9

Take a ruler, measure the height of each curve provided, and compare them in length. From there, you determine the ratio, giving you the # of hydrogens.

Question 10

What do the height of curves correspond to?

Answer 10

the # of hydrogens in the respective peaks.

Question 11

What is the standard used for chemical shift?

Answer 11

Trimethylsilane, located at 0 ppm.

Question 12

What are the units of chemical shift?

Answer 12

ppm

Question 13

What does J coupling involve?

Answer 13

Hydrogens adjacent to other hydrogens can be split into multiple peaks.

Question 14

How can each hydrogen be regarded?

Answer 14

As a magnet; it is either aligned or against the magnetic field.

Question 15

How do you know how many peaks will arise based on the number of adjacent hydrogens?

Answer 15

n+1 (n being the # of hydrogens that another hydrogen is adjacent to).

Question 16

What are the ratios based on the # of adjacent H?

Answer 16

0- Singlet- 1
1- Doublet- 1:1
2- Triplet- 1:2:1
3- Quartet- 1:3:3:1
4- Quintet- 1:4:6:4:1
5- Sextet - 1:5:10:10:5:1

Question 17

Can chemically identical nuclei couple to one another?

Answer 17

No, they cannot.

Question 18

What unit is the spacing between peaks in?

Answer 18

Hertz.

Question 19

In what cases is the coupling constant 7Hz?

Answer 19

In acyclic alkanes, CH’s have a coupling constant of 7Hz.

Question 20

In what cases is the coupling constant different for protons?

Answer 20

In Alkenes; cis protons have a coupling constant of 10Hz and trans protons have a coupling constant of 18Hz.

Question 21

When do you get a doublet of doublets? What’s an example?

Answer 21

When a proton is coupled with 2 different protons with 2 different coupling constants. For example, a hydrogen in an alkene coupling with the cis and then trans hydrogen.

Question 22

What is the ratio of a doublet of doublets and how many peaks do you get?

Answer 22

4 peaks. 1:1:1:1

Question 23

What is the relationship between electron density and chemical shift?

Answer 23

The higher the electron density, the lower the chemical shift. INVERSE.