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
how is a spectra decoupled
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
how is j coupling effected by number of bonds between atoms
more bond = lower coupling
