Unit 4 Flashcards
(27 cards)
What causes nuclei to have spin and a nuclear magnetic charge
An odd atomic number or mass
What does spinning charge do
Create a magnetic field
What are the spin states of an electron
-1/2 and +1/2
What are the two orientations allowed and how do they affect the magenetic field
With the field, decrease in E and agaisnt the field, increase in E
What happens when there is an rf signal that is the same frequency as the magentic moment
The rf signal induces a transition between spin states
What is diamagnetic shielding
a shift in the magnetic field due to electrons inside the molecule that create a weak magnetic field that opposes the applied magnetic field; this causes chemical shifts
What contributes to chemical shifts
induction and hybridization of attached atoms and diamagnetic anisotropy
What is the chemical shift trend
the more electronegative x is, the more chemical shift x will have
What are acetylenic Hs
Hs found on alkanes (single bonds)
What are vinylic Hs
Hs found on alkenes (double bonds)
What is diamagnetic anisotropy
Pi electrons move around a moleule creating a magnetic field that is opposite acetylenic Hs but the same a vinylic Hs
What is coupling constant
symbol J. Is a measure of the magnetic interaction between coupled nuclei
What causes a higher/lower coupling constant
when nuceli are as far apart as possible there is a large J but when very close there is a small J
What are the selection rules for IR absorption
group must be polar and its vibration must cause a periodic change in the bond dipole moment
What molecules are considered IR inactive
symmetrical alkenes and alkymes that would have a dipole moment of 0
What symmetrical molecules have a dipole moment of 0 but are still IR active
Coupled bonds: one bond is stretched while bond on other side is not
What creates a higher wavenumber of vibration AKA stretching at a higher frequency
Stronger bond and lighter atoms
What is the nuclear Overhauser effect
The transition of a nucleus from one spin state to another one
What gives rise to the nuclear Overhauser effect in C NMR
broadband decouping of H
What makes Hs homotopic and are they on the same NMR signal
When substitution makes the same molecule and there is symmetry and they are on the same NMR
What makes Hs enantiotopic and are they on the same NMR signal
When substitution yields a symmetrical molecule and a chiral center and yes on the same NMR signal
What makes Hs diastereotopic and are they on the same NMR signal
When the substitution makes a molecule that is not symmetrical and Hs have different connectivity and will be on different NMR signals
What makes Hs heterotopic and are they on the same NMR signal
When there is no symmetry and there is no chiral center
What is the IR range that a C-O can be found
1000-1250
