Orgo - HNMR

Question 1

Chemical Shift for R-CH3

Answer 1

0.9 - 1.2 ppm

alkyl group (hydrocarbon chain)

Question 2

Chemical Shift for R-CH2

Answer 2

1.2 - 1.5 ppm

alkyl group (hydrocarbon chain)

Question 3

Chemical Shift for R-CH

Answer 3

1.4 - 1.9 ppm

alkyl group (hydrocarbon chain)

Question 4

Chemical Shift for ketone R-C=C—H

Answer 4

2.0 - 2.6 ppm

Question 5

Chemical Shift for R-CH (with O-CH3)

Answer 5

2.2 - 2.5 ppm

Question 6

Chemical Shift for RNH2 (with variable)

Answer 6

variable, 1 - 5 ppm

Question 7

Chemical Shift for C=C-CHR2

Answer 7

1.5 - 2.5 ppm

Question 8

Chemical Shift for Ar - CH3

Answer 8

2.2 - 2.5 ppm

Question 9

Chemical Shift for Ar - H

Answer 9

6.0 - 8.5 ppm

Question 10

Chemical Shift for aldehyde R-CHO

Answer 10

9.5 - 10.5 ppm

Question 11

Chemical Shift for (H)R — 0-CH3

Answer 11

3.3 - 4.0 ppm

Question 12

Chemical Shift for R-OH

Answer 12

variable, 1 - 5 ppm

Question 13

Chemical Shift for X-CH,R (X: Cl, Br, I)

Answer 13

3.1 - 3.8 ppm

Question 14

Chemical Shift for R (with C=C.)

Answer 14

4.5 - 6.0 ppm

Question 15

What does ‘downfield’ refer to in NMR spectroscopy?

Answer 15

Deshielded region of the spectrum
high frequency
high chemical shift
more EWG groups

Downfield indicates that the resonance frequency is higher, usually associated with protons that are more electronegative or in an electronegative environment.

Question 16

What does ‘upfield’ mean in NMR spectroscopy?

Answer 16

Shielded region of the spectrum
low chemical shift
low chemical shift
more EDG groups

Upfield indicates that the resonance frequency is lower, usually associated with protons that are less influenced by electronegative atoms.

Question 17

HNMR is good for

Answer 17

measuring red # p and red environments and # adj p , splitting patterns, functional groups

Question 18

How does HNMR work

Answer 18

in an external field protons have magnetic m dipole aligned in alpha (low E) and beta (high E) states. Electrons move levels and excite and different frequencies

Question 19

Effects of stronger magnetic fields in HNMR and direction

Answer 19

when a stronger magnetic field is applied, the energy difference between the alpha and beta spin states of a proton increases, making it more likely for the proton to absorb energy from an electromagnetic radiation source at the right frequency and “flip” its spin state, a phenomenon called nuclear magnetic resonance (NMR) where the nucleus is considered “in resonance” with the applied field

electrons move in one direction and magnetic field is 90 to that

Question 20

Relate deshileding/shielding, frequency and energy

Answer 20

shielding decreases magnitude of magnetic field causing LESS E diff between alpha and beta, LOWER frequency, SMALLER applied magnetic field

deshielding increases magnitude of magnetic field causing MORE E diff between alpha and beta, HIGHER frequency, BIGGER applied magnetic field

Question 21

chemical shift

Answer 21

distance from TMS in Hz / frequency in Hz

TMS = 0

Question 22

diamagnetic anistropy (non uniformity) affect for pi electrons

Answer 22

location of the H matters
especially if pi electrons (conjugated)

Question 23

Which compounds are low number of range above 5 on HNMR?

Answer 23

H off of Alkene
Aldehyde/ketone
Acid

Question 24

Which compounds have variable chemical shifts on HNMR?

Answer 24

R-OH alcohol and R-NH2 amine