Rule C-43 43.1 - In more recent use, particularly for steroids (see Rules 2S-6.1 and
2S-7.1) and higher terpenes, "nor-" denotes (a) elimination of one methylene group from a chain, the highest permissible locant being used, or (b) contraction of a ring
by one CH2 unit, the locant being the capital letter identifying the ring. Elimination of two or more methylene groups may be denoted by the prefixes "dinor-", "trinor-", and so on.
See Recommendations'93 R-1.2.5
Examples to Rule C-43.1
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