Repeating units represent structural parts that can be repeated several times. The repeating unit is enclosed in brackets with one or two head and the same number of tail crossing bonds. (Head crossing bonds go through the left bracket.) Two bond pairs represent ladder type repeating units. The repetition range is a comma-separated list of possible repetitions or repetition intervals, e.g. "1,3,5-9". The repetition pattern specifies the way how the subsequent repeated units are linked together: it can be head-to-head(hh), head-to-tail(ht) or either/unknown(eu) (the either/unknown case is not handled by the search software). In case of ladder type polymers there is also a flip(f) option that defines that the top and bottom crossing bonds are flipped during each connection. repeating groups with specified repetition ranges.
Repeating unit drawing is described in the Marvin Sketch Help here , and ladder-type bracket drawing is described at the polymer drawing section.
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