Quiz 1 - NMR

Question 1

Proton NMR is a technique that uses ____ to study the ____ in a sample

Answer 1

Proton NMR is a technique that uses NUCLEAR MAGNETIC RESONANCE to study the HYDROGEN ATOMS in a sample

Question 2

In an NMR experiment, shielding refers to the reduced impact of the ____ on a nucleus due to the presence of _____ around the nucleus.

Answer 2

In an NMR experiment, shielding refers to the reduced impact of the APPLIED MAGNETIC FIELD on a nucleus due to the presence of ELECTRONS around the nucleus

Question 3

Shielding can be _____ by the presence of more electronegative groups around the nucleus.

Answer 3

Shielding can be DECREASED by the presence of more electronegative groups around the nucleus.

Question 4

A shielded nucleus appears further ____ whereas a deshielded nucleus appears further ____ in an NMR spectrum.

Answer 4

A shield nucleus appears further UPFIELD whereas a deshielded nucleus appears further DOWNFIELD in an NMR spectrum.

Question 5

splitting

Answer 5

The appearance of multiple peaks for a single nucleus due to neighboring nuclei is called this

Question 6

integration

Answer 6

The area of a signal that corresponds to the number of nuclei at that frequency is called this

Question 7

The end of the NMR spectrum far from the reference signal is called this

Answer 7

downfield

Question 8

The end of the NMR spectrum close to the reference signal is called this

Answer 8

upfield

Question 9

chemical shift

Answer 9

The frequency at which a nucleus absorbs and resonates with a magnetic field is called this

• in ppm

Question 10

what type of id test is NMR?

Answer 10

qualitative and quantitative

Question 11

How does NMR work?

Answer 11

• Nuclei have spin property from intrinsic angular momentum
• Moving charges generate magnetic fields based on number of protons
• Must have net +/- charge to be active (not even N and p)

Question 12

alpha VS beta spin states

Answer 12

Alpha = low energy and parallel H’s
Beta = high energy and anti-parallel H’s

Question 13

NMR procedure

Answer 13

1. Expose sample to external magnetic field.
2. Separate protons into alpha and beta spin states.
   3.Measure the difference between spin states
3. Energy difference associated with different frequencies of magnetic radiation
4. Electromagnetic radiation excites protons from A to B spin states
5. Protons relax down to A state and emit energy in the process
   7.Energy at a specific resonant frequency which is detected and plotted for NMR spectrum

***Energy depends upon chemical environment of nuclei.

Question 14

number of signals

Answer 14

Number of chemical environments
Unique groups of chemical equivalent H-atoms

Question 15

deshielded

Answer 15

Deshielded (less ED) ⇒ more EN atoms close by (> +)
Downfield with larger ppm

Question 16

shielded

Answer 16

Shielded (more ED) ⇒ less EN atoms close by (> -)
Upfield with smaller ppm

Question 17

standard 0 ppm value

Answer 17

TMS (tetramethylsilane)

Question 18

Chemical shift in rings

Answer 18

remember ortho, para, and meta positions being controlled by EWG (more EN) vs EDG (less EN)

Question 19

Factors that affect chemical shift

Answer 19

• ED ⇒ inductive withdrawing from EN atoms/nearby (+/-)s OR resonance
• H-bonding
• Solvent effects
• Rings

Question 20

splitting patterns

Answer 20

• Signals are split into multiple peaks based on the number of adjacent H-atoms (3 bonds away)

Question 21

coupled

Answer 21

• Occurs when H’s in one environment interact with H’s in a different chemical environment
• spilt into multiple peaks
• *** H’s cannot couple with H’s in same chemical environment

Question 22

n + 1 rule

Answer 22

• The number of peaks is equal to the number of H’s 3 bonds away plus one
  *can only occur through hydrocarbon bonding
• used to determine the number of peaks per signal (signal pattern)

Question 23

Degrees of Unsaturation (DU)

Answer 23

-How many rings/pi bonds are present in a molecule

Equation = 2(carbons) + 2 - nitrogens - hydrogens - halogens2

Question 24

J (coupling constant)

Answer 24

the distanced between coupled peaks
- larger distance = larger J in Hz