I wonder whether you could put this as an entry on your blog. Originally, it ought to be a comment on your last entry, but then it grew …
Concerning the chains of CH2 groups with convergent chemical shifts, I would like to point out another mechanism which has similar NMR consequences and leads inevitably to strong couplings even at the highest fields (present and future):
Consider a chain of the -(CH2)n-R attached to a chiral carbon:
with the substituents S1,S2 and S3 all distinct. The chirality of the first carbon is explicit, so I will say that it is first-order. Now, when R is not a proton, Ha and Hb have different chemical shifts. But this means that the two protons are not equivalent and therefore the second carbon is also chiral (let us call this the induced chirality of second-order). Which means that the protons Hc and Hd in the second formula are also chemically distinct, etc. This logic carries on iteratively, leading to induced chiralities of ever higher orders.
BTW, I wonder whether the adjective "induced" might not be more proper also in the context of virtual coupling you were writing about in your last entry. Maybe "induced coupling" would be a bit less controversial. Though I am not sure. You could propose it for an e-poll. Ciao, Stan