1885 47 804 Another method for forming these ring-compounds was..afterwards found.
1932 Aug. 246/1 A half-way stage between the most stable kind of carbon chain compound, and the most stable kind of ring compound.
1988 J. D. Barrow & F. J. Tipler (rev. ed.) viii. 549 The purines adenine and guanine, and the pyrimidines cytosine, uracil, and thymine,..are ring compounds with two nitrogen atoms per ring.