Lewis acids and bases ionic bonding. Classically, the term "Lewis acid" is restricted to trigonal planar species with an empty p orbital, such as BR where R can be an organic substituent or a halide. For the purposes of discussion, even complex compounds such as EtAlCl and AlCl are treated as trigonal planar Lewis acids. Metal ions such as Na, Mg, and Ce, which are invariably complexed with additional ligands, are often sources of coordinatively unsaturated derivatives that form Lewis adducts upon reaction with a Lewis base[citation needed]. Other reactions might simply be referred to as "acid-catalyzed" reactions. Some compounds, such as HO, are
CSX milepost prefixes in Waycross, Georgia, 587 miles south of Richmond on the branch to Montgomery, Alabama (which splits near milepost 548 in Jesup). Three-letter prefixes are used for minor branches of these branches, or minor branches off the mainline - for instance ANA is the northernmost branch of AN. Before the ACL merged into the Seaboard Coast Line Railroad in 1967, none of the prefixes had the initial "A". The letters "I" and "Q" were skipped, and double-lettered prefixes (like KK, which would be AKK post-1967) were not used. A is given to the main line from Richmond, Virginia to Port of