Topic 2: NMR

Question 1

What kind of frequency does Nuclear Magnetic Resonance use?

Answer 1

radio

Question 2

Why are radio waves used for NMR?

Answer 2

provides the right amount of energy for atom’s nuclear spin to be flipped

Question 3

The amount of energy needed to flip a certain atom’s nuclear spin depends on the ______

Answer 3

chemical environment around it (how many and what kind of atoms are bonded to it)

Question 4

NMR spectrum is a plot showing the frequencies at which __________ is absorbed

Answer 4

radio electromagnetic radiation

Question 5

Energy is absorbed when the nucleus of an atom flips from a ____ energy spin state to a _____ energy spin state

Answer 5

low, high

Question 6

Nuclei are NMR active is they have an ___ number of protons and/or nuetrons

Answer 6

odd

Question 7

The alpha spin state is _____ in energy than the beta spin state

Answer 7

lower

Question 8

Protons on the same carbon are equivalent unless they are on an ___ carbon or next to a _____

Answer 8

sp2, chiral center

Question 9

______ or _______ in the molecule can make protons equivalent

Answer 9

symmetry; free bond rotation

Question 10

Hydrogens across sp2 hybridized double bonds are/are not equivalent

Answer 10

are not

Question 11

enantiotopic protons are _____ and will appear as one signal

Answer 11

chemically equivalent

Question 12

How do you define an enantiotopic proton?

Answer 12

If you replace one of two protons on the same carbon with X, and it forms enantiomers, then the protons are enantiotopic

Question 13

diasteriotopic protons are/are not equivalent and will/will not appear as its own signal

Answer 13

are not; will

Question 14

Shielded protons are ____ protected from the magnetic field by its electrons

Answer 14

more

Question 15

Deshielded protons are ____ exposed to the magnetic field

Answer 15

more

Question 16

Shielded protons have a ____ magnetic force acting on them causing a ____ chemical shift which leaves them _____ on an NMR

Answer 16

smaller, lower, upfield

Question 17

Deshielded protons are ____ on an NMR because they have a ____ chemical shift

Answer 17

downfield, higher

Question 18

alkane protons (sp3 C-H) appear below

Answer 18

5 ppm

Question 19

saturated alkanes are _____ _______ and appear around ____ ppm

Answer 19

highly shielded, 1-2

Question 20

_______ bonds create a larger shielding effect and CH bonds are ______

Answer 20

non-polar, non-polar

Question 21

an increase in hydrogens is a decrease in ____

Answer 21

ppm

Question 22

methyl ppm (CH3)

Answer 22

0.9

Question 23

methylene ppm (CH2)

Answer 23

1.2

Question 24

methine ppm (CH)

Answer 24

1.7