J-Coupling Flashcards
how does J-coupling depend on Bo
it doesnt
what do alpha and beta represent
alpha = spin up nucleus beta = spin down nucleus
why does a nucleus coupled to another split
interacts with the spin up and spin down versions
how do energy levels lie in a homonuclear spin system
3 levels
ab = ba
how do energy levels lie with heteronuclear spins
4 levels
how many transitions in a homonuclear system and what are they
aa-ab
aa-ba
ab-bb
ba-bb
why can aa-bb or ab to ba
M = +/- 1
when does a 3 spin system show as a triplet
when J12 = J13
what splitting does AX2 form
triplet
what splitting does AX3 form
quartet
what splitting does AMX form
doublet of doublets
how does AX of a 3/2 spin nuclei split
1:1:1:1
when does roofing occur
when J > ^v
why were early NMR spectra hard to analyse
low field strength often meant J > ^v
why can strong coupling be reduced by increasing field strength
because ^v is proportional to Bo
what are 4 properties of scalar coupling
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
how does J coupling relate to s character
J coupling is ~ 500x s character
how does electronegativity affect J coupling
greater electronegativity = larger J coupling
how does ring strain effect J coupling
ring strain increases J coupling
how does coordination affect j coupling
increased coordination decreases J coupling - less s characterq
what is the formula for J coupling at an angle
3JHH = 2 - cos(theta) + 10cos^2(theta)
what is the value of coupling at 0 degrees
~11
what is the value of coupling at 90 degrees
~2
what is the value of coupling at 180 degrees
~11
