Redraw queue

The redraw queue is the source from which atoms are drawn during the assembly phase (see below). It is initialized to one (more or less arbitrary) atom. Whenever an atom is placed, its as-yet-unplaced neighbors are inserted into the queue. The queue should be sorted by atom priority (see later section on Atom Prioritization), such that the next atom withdrawn is the most strategic of those residing in the queue. 

After a neighbor has been placed, it is itself added to the redraw queue. Because the order in which atoms are drawn from the queue influences their tendency to overlap, the queue is prioritized, and more sterically demanding atoms are drawn earlier when choice exists (see below on Combating Overlap). 

It is not critical where atom placement begins. However, opportunities for eventual atom overlap are lessened when one starts with a more centrally located atom. Most authors have recommended beginning with a highly substituted site, typically a ring atom. We likewise begin with the highest priority atom, as quantified by Shelley (see section above on Atom Prioritization). This atom is pushed onto the redraw queue, hitherto empty. The first atom placed in a fragment is called the head atom. ... 

Redrawing proceeds by removing from the redraw queue its highest priority atom, which will be referred to as the seed atom. With the exception of the first (head) atom, the seed atom has already been placed it is its neighbors that are of interest. The head atom is unique because there is no other atom, already placed, to which it can attach. The head atom is placed at its incoming position, unless it is part of a PFU, in which case that position is used. If one is drawing de novo, its location is arbitrary. 

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