1H NMR

Question 1

What is the highest chemical shift value you will find for 1H NMR and why

Answer 1

Aldehyde ~10
The inductive effect from oxygen is delocalising electron density onto itself, decreasing electron density on the carbon

Question 2

What is the chemical shift for 1H NMR for a proton adjacent to Nitrogen in pyridine

Answer 2

Pyridines Nitrogen will pull electron density away from the carbon having an inductive effect, hence increasing the chemical shift

Question 3

What is the chemical shift for a 1H NMR spectrum for an aromatic hydrogen

Answer 3

~7
Electron density above and below the plane, results in carbons in the plane being electron deficient (inductive effect)

Question 4

What is the chemical shift for an alkene in 1H NRM spectrum

Answer 4

~6
Having electron density above and below the plane, will make carbons within the plane electron deficient

Question 5

What is the chemical shift for ethers and esters in 1H NMR

Answer 5

~3.5-4
the oxygen will draw electron denisty towards itself, increasing electron deficiency of the hydrogens
(amides would be ~2.5-3 for same reason)

Question 6

Answer 6

Due to delocalistion, positive charge occurs at the carbons of Ha and Hc
Hence are more electron deficient and are likely to appear at higher frequencies

Question 7

What is the chemical shift of ketone on 1H NMR spectra

Answer 7

~2ppm
carbonyl will shift away electron density, but value is lower than an aldehyde because it is one atom further away

Question 8

What is the chemical shift of a benzylic and allylic hydrogen on 1H NMR
(allylic is 1C after the dbl bond of an alkene)

Answer 8

~2 ppm
anisotropy in the electron density
electron density from the benzene ring and double carbon bond, increase the electron deficiency of these hydrogens
effect is less because they are further away

Question 9

What is the chemical shift of a terminal alkyne on 1H NMR

Answer 9

~2
electron density from the triple bond with increase the electron deficiency in the hydrogen on the CH₃ group
The effect the the triple bond is less than the double bond (same ppm but one carbon removed in alkenes)

Question 10

What is the chemical shift of your standard CH₂ group on 1H NMR spectrum

Answer 10

~1 to 2
(adjacent methylene group will pull electron density away, increasing electron deficiency)

Question 11

What is the group responsible for the lowest chemical shift seen on 1H NMR

Answer 11

Methyl (CH₃)
ppm around 1

Question 12

What is a good rule of thumb when trying to remeber coupling constants

Answer 12

Many coupling constants (in terms of magnetic interaction) are about 7 Hz

Question 13

Which J-Coupling constants have a value ~7Hz

Answer 13

• sp3 to sp3
• sp3 to sp2
• benzene (8Hz)
• sp2 to sp2 in 5-membered aromatics (6Hz)
• cis alkenes (6-11Hz)

Question 14

Which J-Coupling constants have a value ~14Hz
(7x2)

Answer 14

• trans double bond (better overlap)
• J-gem on sp3

Question 15

Which J-Coupling constants have a value close to 0

Answer 15

• small rings (3Hz)
• near orthogonal hydrogens on alkenes (0-1Hz)
• 4 bond coupling on benzene (2Hz)
• terminal alkynes (3Hz)
  These values are typically small because of the limited overlap between orbitals