Micro view of NMR - Revision history

Milllo: /* Spectra */

2020-04-20T12:47:47Z

Spectra

72.12.192.208: /* Peak Splitting */

2020-04-17T00:38:32Z

Peak Splitting

72.12.192.208: /* Peak Splitting */

2020-04-17T00:38:20Z

Peak Splitting

Milllo: /* Quantum transitions in nuclei */

2020-04-15T01:33:28Z

Quantum transitions in nuclei

Milllo: /* Relaxation */

2020-04-14T21:10:58Z

Relaxation

Milllo: /* Relaxation */

2020-04-14T21:10:32Z

Relaxation

Milllo: /* Relaxation */

2020-04-14T20:33:01Z

Relaxation

Milllo: /* Relaxation */

2020-04-14T20:23:00Z

Relaxation

Milllo: /* Relaxation */

2020-04-14T20:21:03Z

Relaxation

Milllo: /* Relaxation */

2020-04-14T20:20:46Z

Relaxation

@@ Line 15: / Line 15: @@
 ==Spectra==
-To obtain a spectrum, a spin 1/2 atom must first be placed into a static magnetic field to cause separation of the two states. The amount of separation depends on the [[gyromagnetic ratio]] (gamma) (<span style="font-family:symbol;">g</span>) for that element (a constant) and the intensity of the static magnetic field (B<sub>0</sub>) according to the [[Derivation of Larmor frequency equation|derived equation]]:
+To obtain a spectrum, a spin 1/2 atom must first be placed into a static magnetic field to cause separation of the two states. The amount of separation depends on the [[gyromagnetic ratio]] (gamma) (<span style="font-family:symbol;">g</span>) for that element/elementary particle (a constant) and the intensity of the static magnetic field (B<sub>0</sub>) according to the [[Derivation of Larmor frequency equation|derived equation]]:
 v<sub>0</sub>=<span style="font-family:symbol;">g</span>*B<sub>0</sub>

@@ Line 92: / Line 92: @@
 Fortunately, electrons in bonds are paired and have net spin 0, so they don't have multiple states when placed in a magnetic field. Carbons also have net spin 0 so they don't have multiple states either (<sup>13</sup>C does have two states but is present at only 1.1% of total carbon). Therefore the only source of multiple states in ethanol is other hydrogens. In a sample, the total <sup>1</sup>H population is split into two for each <sup>1</sup>H on the molecule due to the Boltzmann distribution as described previously. So the methyl protons in ethanol see four different environments due to the two populations of each <sup>1</sup>H on the neighboring CH<sub>2</sub>. Four different magnetic environments thus leads to 4 different peaks for the methyl. Symmetry of the CH<sub>2</sub> means that two of the four overlap, resulting in three peaks, with the central peak double in size.
-[[File:splitting.gif|300px]]
+[[File:splitting.gif|600px]]
 Following the same logic, the CH<sub>2</sub> in ethanol will have 6 peaks due to 6 different environments, two environments for each <sup>1</sup>H in the methyl, with 4 of them overlapping due to symmetry of the methyl protons, resulting in a quartet.

@@ Line 92: / Line 92: @@
 Fortunately, electrons in bonds are paired and have net spin 0, so they don't have multiple states when placed in a magnetic field. Carbons also have net spin 0 so they don't have multiple states either (<sup>13</sup>C does have two states but is present at only 1.1% of total carbon). Therefore the only source of multiple states in ethanol is other hydrogens. In a sample, the total <sup>1</sup>H population is split into two for each <sup>1</sup>H on the molecule due to the Boltzmann distribution as described previously. So the methyl protons in ethanol see four different environments due to the two populations of each <sup>1</sup>H on the neighboring CH<sub>2</sub>. Four different magnetic environments thus leads to 4 different peaks for the methyl. Symmetry of the CH<sub>2</sub> means that two of the four overlap, resulting in three peaks, with the central peak double in size.
-[[File:splitting.gif|400px]]
+[[File:splitting.gif|300px]]
 Following the same logic, the CH<sub>2</sub> in ethanol will have 6 peaks due to 6 different environments, two environments for each <sup>1</sup>H in the methyl, with 4 of them overlapping due to symmetry of the methyl protons, resulting in a quartet.

@@ Line 1: / Line 1: @@
 ==Quantum transitions in nuclei==
-NMR from a micro-point of view is an instrumental technique that uses photons of radio frequency energy to cause a transition, or change in state, in an atom. Radio is used because the amount of energy needed to cause these transitions happens to fall in the radio region of the [[electromagnetic spectrum]]. The transitions are also quantized, which means there has to be the right amount of energy to cause a change of state, too much or too little and no change occurs.
+NMR from a micro-point of view is an instrumental technique that uses photons of radio frequency energy to [[Resonance in NMR|cause]] a transition, or change in state, in an atom. Radio is used because the amount of energy needed to cause these transitions happens to fall in the radio region of the [[electromagnetic spectrum]]. The transitions are also quantized, which means there has to be the right amount of energy to cause a change of state, too much or too little and no change occurs.
 There are many quantum transitions in atoms, but the ones manipulated in NMR are [[Quantum spin|quantum spin]] transitions. Quantum spin has two states, often referred to as "up" and "down". In a natural environment these two states are equivalent in energy, so an atom could be in one or the other at any time with no change in energy. However, when the atom is placed in a strong magnetic field the states become non-equivalent, with one of the states a little higher in energy than the other. '''This difference in energy is the key to NMR.''' A photon with this amount of energy can then be shot at the atom, which will absorb it and cause a transition between the 'up' and 'down' spin states. Thus light can be used to probe substances at the atom level!

@@ Line 107: / Line 107: @@
 bottom axis is time in seconds
-A good way to think of it is hitting a bell with a hammer. Even though the initial impulse of the hammer is over, the bell continues to ring at the same frequencies but with intensity decreasing over time.
+A good way to think of it is hitting a bell with a hammer. Even though the initial impulse of the hammer is over, the bell continues to ring at the same frequencies but with decreasing intensity over time.
 The delay in states relaxing back to equilibration occurs due to several mechanisms:

@@ Line 121: / Line 121: @@
 [[Relaxation of spin 1/2 nuclei: transition probabilities|Relaxation Math - transition probabilities]]
-The equations for relaxation are complex and generally involve two numbers: the spin-lattice relaxation time T<sub>1</sub> and the spin-spin relaxation time T<sub>2</sub>.
+The equations for relaxation are complex and generally involve two numbers: the spin-lattice relaxation time T<sub>1</sub> and the spin-spin relaxation time T<sub>2</sub>. Because both mechanisms are happening at the same time it is difficult to measure them independently, so a number of unique experiments have been designed to try to minimize the overlap in the times.
 ==Related topics==

← Older revision		Revision as of 20:23, 14 April 2020
Line 120:		Line 120:

	[[Relaxation of spin 1/2 nuclei: transition probabilities\|Relaxation Math - transition probabilities]]		[[Relaxation of spin 1/2 nuclei: transition probabilities\|Relaxation Math - transition probabilities]]
		+
		+	The equations for relaxation are complex and generally involve two numbers, the spin-lattice relaxation time T<sub>1</sub> and the spin-spin relaxation time T<sub>2</sub>.

	==Related topics==		==Related topics==

← Older revision		Revision as of 20:21, 14 April 2020
Line 118:		Line 118:

	[[Relaxation of spin 1/2 nuclei: two-state derivation\|Relaxation Math - 2 states]]		[[Relaxation of spin 1/2 nuclei: two-state derivation\|Relaxation Math - 2 states]]
		+
	[[Relaxation of spin 1/2 nuclei: transition probabilities\|Relaxation Math - transition probabilities]]		[[Relaxation of spin 1/2 nuclei: transition probabilities\|Relaxation Math - transition probabilities]]

@@ Line 117: / Line 117: @@
 * Paramagnetic
-[[Relaxation of spin 1/2 nuclei: two-state derivation|Relaxation Math]]
+[[Relaxation of spin 1/2 nuclei: two-state derivation|Relaxation Math - 2 states]]
 ==Related topics==