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Notes for Midterm 2 Chem 6AL

Notes for Midterm 2 Chem 6AL - Ch 21 Notes-H1 and C13 both...

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Ch 21 Notes -H1 and C13 both have spins of ½ -If both atomic number and mass number even= nuclear spin of 0= NO NMR SIGNAL PRODUCED -Energy levels allowed= 2I +1 THEREFORE H1 and C13 both E levels allowed=2 -Without applied magnetic field, the two E levels are degenerate (same energy) -When applied B field, they separate into two levels===> alpha and Beta -Alpha decreases in E -Beta increases in E -Delta E is PROPORTIONATE to the strength of the B field FOR FT NMR's THIS IS HOW SIGNALS OCCUR -NMR signals occur during RELAXATION -DEFINE: RELAXATION= when a nucleus in the higher E state (Beta) drops to a lower E state (alpha) and emits a quantum of E -ALPHA --- Nuclear magnetic dipole aligned with B field THEREFORE nucleus spin with B field - BETA ---Nuclear magnetic dipole opposed to B field THEREFORE nucleus spin opposed B field ----- ENERGY MUST BE ABSORBED TO SWITCH FROM ALPHA TO BETA and TO SWITCH FROM ALIGNED TO OPPOSED ( makes sense cuz easier to go with rotate with b field then to oppose, so more E must be put in to system to oppose) - NMR SOLVENTS -ideally want a chemical solvent that is inert, THEREFORE will not absorb E in the B field THEREFORE for H1, want a solvent that has NO PROTONS THEREFORE want a deuterium solvent -Most commonly used deuterium solvent= deuterated chloroform which is usualy 99.8% pure
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