electromagnetic spectrum
the different forms of electromagnetic radiation make up the electromagnetic spectrum
nuclear magnetic resonance spectroscopy
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”
nuclear spin states
- 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
Nuclear spins in an external magnetic field
- 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
resonance
-the transition from the lower state to the higher occurs at a unique combinations of magnetic field and frequency of electromagnetic radiation
chemical shift
the difference in resonance frequencies for hydrogens
signal areas
-relative signal areas are proportional to the number of H giving rise to each signal
equivalent hydrogens
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
signal splitting
-splitting of an NMR signal into a set of peaks by the influence of neighboring nonequivalent hydrogens
origins of signal splitting
-when the chemical shift of one nucleus is influenced by the spin of another, the two are coupled
peak
the units into which an NMR signal is split; doublet, triplet, quartet, multiplet, etc
(n+1) rule
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
singlet
1
doublet
1:1
triplet
1:2:1
quartet
1:3:3:1
alkanes
- 1HNMR appear in range of 0.8-1.7
- 13CNMR appear in range of 10-60
alkenes
-1HNMR appear at 4.6-5.7
13CNMR appear at 100-160
alcohols
-1HNMR OH chemical shift in range 3.0-4.0 but may be as low as 0.5
ethers
1HNMR appear at 3.3-4.0
aldehydes & ketones
- 1HNMR aldehyde at 9.5-10
- 1HNMR alpha hydrogens at 2.2-2.6
- 13CNMR carbonyl carbons at 180-215
amines
-1HNMR appear at 0.5-5.0
carboxylic acids
- 1HNMR appear at 10-13
- 13CNMR appear at 160-180
