(i) lowest locants to the principal groups;
(ii) lowest locants to the hetero atoms considered together, and if there is a choice, to the hetero atoms cited first in Table B-I of Rule B-1. In the order of precedence any "onia" prefix follows the corresponding "a" prefix
(iii) according to the principles stated in Rules A-3.1, A-3.2, A-3.3, and A-3.4.
See Recommendations'93 R-1.2.2
Examples to Rule C-62.1
(Note: In polyesters named by this method the locants of carbonyl groups differ by unity from the locants of oxa groups. Similar differences apply in the names of polyamides.)
(cf Rule D-1.5)
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