J-Coupling

Question 1

how does J-coupling depend on Bo

Answer 1

it doesnt

Question 2

what do alpha and beta represent

Answer 2

alpha = spin up nucleus
beta = spin down nucleus

Question 3

why does a nucleus coupled to another split

Answer 3

interacts with the spin up and spin down versions

Question 4

how do energy levels lie in a homonuclear spin system

Answer 4

3 levels

ab = ba

Question 5

how do energy levels lie with heteronuclear spins

Answer 5

4 levels

Question 6

how many transitions in a homonuclear system and what are they

Answer 6

aa-ab
aa-ba
ab-bb
ba-bb

Question 7

why can aa-bb or ab to ba

Answer 7

M = +/- 1

Question 8

when does a 3 spin system show as a triplet

Answer 8

when J12 = J13

Question 9

what splitting does AX2 form

Answer 9

triplet

Question 10

what splitting does AX3 form

Answer 10

quartet

Question 11

what splitting does AMX form

Answer 11

doublet of doublets

Question 12

how does AX of a 3/2 spin nuclei split

Answer 12

1:1:1:1

Question 13

when does roofing occur

Answer 13

when J > ^v

Question 14

why were early NMR spectra hard to analyse

Answer 14

low field strength often meant J > ^v

Question 15

why can strong coupling be reduced by increasing field strength

Answer 15

because ^v is proportional to Bo

Question 16

what are 4 properties of scalar coupling

Answer 16

independent of Bo
depend on s character of bonding electrons
depends on the number of bonds between coupling nuclei
is proportional to the product of gyromagnetic ratios of the 2 nuclei

Question 17

how does J coupling relate to s character

Answer 17

J coupling is ~ 500x s character

Question 18

how does electronegativity affect J coupling

Answer 18

greater electronegativity = larger J coupling

Question 19

how does ring strain effect J coupling

Answer 19

ring strain increases J coupling

Question 20

how does coordination affect j coupling

Answer 20

increased coordination decreases J coupling - less s characterq

Question 21

what is the formula for J coupling at an angle

Answer 21

3JHH = 2 - cos(theta) + 10cos^2(theta)

Question 22

what is the value of coupling at 0 degrees

Answer 22

~11

Question 23

what is the value of coupling at 90 degrees

Answer 23

~2

Question 24

what is the value of coupling at 180 degrees

Answer 24

~11

Question 25

how is a spectra decoupled

Answer 25

sample is irradiated at resonance frequency of peak of coupling nuclei
induces rapid transitions of spin
removes the nucleus and any splittings caused by it from the spectrum

Question 26

how is j coupling effected by number of bonds between atoms

Answer 26

more bond = lower coupling