NMR

Question 1

electromagnetic spectrum

Answer 1

the different forms of electromagnetic radiation make up the electromagnetic spectrum

Question 2

nuclear magnetic resonance spectroscopy

Answer 2

a spectroscopic technique that gives us info about the number and types of atoms in a molecule about the number and types

• if the nucleus is irradiated with radiation having energy that is exactly the same as the difference btw the nuclear spin states, energy is absorbed and the nuclear spin is flipped from spin state +1/2 to -1/2
• low frequency radiation is needed to induce spin “flips”

Question 3

nuclear spin states

Answer 3

• nuclei with an odd mass, an odd atomic number, or both also have a net spin and a resulting nuclear magnetic moment
• for each I (quantum number) there are 2I + 1 spin states
• if I = 1/2, there are two allowed spin states

Question 4

Nuclear spins in an external magnetic field

Answer 4

• within a collection 1H and 13C atoms, nuclear spins are completely random in orientation
• when placed in external magnetic field, it is quantized
• allowed spin states increases linearly with applied field strength

Question 5

resonance

Answer 5

-the transition from the lower state to the higher occurs at a unique combinations of magnetic field and frequency of electromagnetic radiation

Question 6

chemical shift

Answer 6

the difference in resonance frequencies for hydrogens

Question 7

signal areas

Answer 7

-relative signal areas are proportional to the number of H giving rise to each signal

Question 8

equivalent hydrogens

Answer 8

hydrogens that have the same chemical environment

• a molecule with 1 set of equivalent hydrogens gives 1 NMR signal
• a molecule with 2 or more sets of equiv hydrogens give different NR signal for each set

Question 9

signal splitting

Answer 9

-splitting of an NMR signal into a set of peaks by the influence of neighboring nonequivalent hydrogens

Question 10

origins of signal splitting

Answer 10

-when the chemical shift of one nucleus is influenced by the spin of another, the two are coupled

Question 11

peak

Answer 11

the units into which an NMR signal is split; doublet, triplet, quartet, multiplet, etc

Question 12

(n+1) rule

Answer 12

if a hydrogen has n hydrogens nonequivalent to it but equivalent among themselves on the same or adjacent atoms, its 1H-NMR signal is split into (n+1) peaks

Question 13

singlet

Answer 13

1

Question 14

doublet

Answer 14

1:1

Question 15

triplet

Answer 15

1:2:1

Question 16

quartet

Answer 16

1:3:3:1

Question 17

alkanes

Answer 17

• 1HNMR appear in range of 0.8-1.7

- 13CNMR appear in range of 10-60

Question 18

alkenes

Answer 18

-1HNMR appear at 4.6-5.7

13CNMR appear at 100-160

Question 19

alcohols

Answer 19

-1HNMR OH chemical shift in range 3.0-4.0 but may be as low as 0.5

Question 20

ethers

Answer 20

1HNMR appear at 3.3-4.0

Question 21

aldehydes & ketones

Answer 21

• 1HNMR aldehyde at 9.5-10
• 1HNMR alpha hydrogens at 2.2-2.6
• 13CNMR carbonyl carbons at 180-215

Question 22

amines

Answer 22

-1HNMR appear at 0.5-5.0

Question 23

carboxylic acids

Answer 23

• 1HNMR appear at 10-13

- 13CNMR appear at 160-180