Unit 4

Question 1

What causes nuclei to have spin and a nuclear magnetic charge

Answer 1

An odd atomic number or mass

Question 2

What does spinning charge do

Answer 2

Create a magnetic field

Question 3

What are the spin states of an electron

Answer 3

-1/2 and +1/2

Question 4

What are the two orientations allowed and how do they affect the magenetic field

Answer 4

With the field, decrease in E and agaisnt the field, increase in E

Question 5

What happens when there is an rf signal that is the same frequency as the magentic moment

Answer 5

The rf signal induces a transition between spin states

Question 6

What is diamagnetic shielding

Answer 6

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

Question 7

What contributes to chemical shifts

Answer 7

induction and hybridization of attached atoms and diamagnetic anisotropy

Question 8

What is the chemical shift trend

Answer 8

the more electronegative x is, the more chemical shift x will have

Question 9

What are acetylenic Hs

Answer 9

Hs found on alkanes (single bonds)

Question 10

What are vinylic Hs

Answer 10

Hs found on alkenes (double bonds)

Question 11

What is diamagnetic anisotropy

Answer 11

Pi electrons move around a moleule creating a magnetic field that is opposite acetylenic Hs but the same a vinylic Hs

Question 12

What is coupling constant

Answer 12

symbol J. Is a measure of the magnetic interaction between coupled nuclei

Question 13

What causes a higher/lower coupling constant

Answer 13

when nuceli are as far apart as possible there is a large J but when very close there is a small J

Question 14

What are the selection rules for IR absorption

Answer 14

group must be polar and its vibration must cause a periodic change in the bond dipole moment

Question 15

What molecules are considered IR inactive

Answer 15

symmetrical alkenes and alkymes that would have a dipole moment of 0

Question 16

What symmetrical molecules have a dipole moment of 0 but are still IR active

Answer 16

Coupled bonds: one bond is stretched while bond on other side is not

Question 17

What creates a higher wavenumber of vibration AKA stretching at a higher frequency

Answer 17

Stronger bond and lighter atoms

Question 18

What is the nuclear Overhauser effect

Answer 18

The transition of a nucleus from one spin state to another one

Question 19

What gives rise to the nuclear Overhauser effect in C NMR

Answer 19

broadband decouping of H

Question 20

What makes Hs homotopic and are they on the same NMR signal

Answer 20

When substitution makes the same molecule and there is symmetry and they are on the same NMR

Question 21

What makes Hs enantiotopic and are they on the same NMR signal

Answer 21

When substitution yields a symmetrical molecule and a chiral center and yes on the same NMR signal

Question 22

What makes Hs diastereotopic and are they on the same NMR signal

Answer 22

When the substitution makes a molecule that is not symmetrical and Hs have different connectivity and will be on different NMR signals

Question 23

What makes Hs heterotopic and are they on the same NMR signal

Answer 23

When there is no symmetry and there is no chiral center

Question 24

What is the IR range that a C-O can be found

Answer 24

1000-1250

Question 25

What is the IR range that a C=C can be found

Answer 25

1600-1680

Question 26

What is the IR range that a CH3 can be found

Answer 26

1375 and 1450

Question 27

What is the IR range that a C=C (aromatic) can be found

Answer 27

1450-1600