As Dan said,
we know that Cs bearing H atoms can only give a peak in NMR,
Middle two Cs doesnt have any Hs so no peaks from these middle two,
the remaining Cs are equivalent, i.e. each one surrounded by same no of Hs(here each H & Cs is equialent) and so same amount of hinderence experienced by both the Cs)
thats why only one peak is observed for both the carbons..
Anand
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