Viva Survivor: Baldwin's rules

This is the first of the basic science posts we will be running about once a week; first up is Baldwin's rules (or guidelines as many prefer), for more detail look here. 

Baldwin’s rules are empirical observations of possible cyclisation reactions, classified according to the size of the ring being formed, the nature of the electrophilic portion of the molecule and whether the bonds are broken inside or outside of the ring.  Although the based on empirical observation they use stereochemical reasoning including orbital overlap and the preferred angle of attack of a nucleophile. Because they are essentially empirical they are not really rules in the Woodwood—Hoffman sense of the word, but should be thought of as guidelines; there are exceptions!