IN paper: Journal of natural products.2000,Vol:63 page#876-878.
Q: An alternative method of the measuring coupling constants in
symmetrically coupled spin systems might be selective deuteration.
Suppose that the proton(a) position (figure 3a)is deuterated. describe
what would you expect to observe in the normal H-NMR spectrum (no BIRD
, just 90 degree excitation pulse). why this much simpler method is
less reliable and precise than the BIRD technique?

Please notice that i need the answer within a week or less , but not
more than a week.