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 CSX milepost prefixes Most CSX railroad lines are given lettered prefixes before milepost numbers. These prefixes are one to three letters long with the first letter usually refer to the former company. For instance, prefixes beginning with "S" were part of the Seaboard Air Line Railroad. Some of these company prefixes include the following: Lines that were formerly part of the Atlantic Coast Line Railroad system are given milepost prefixes beginning with the letter A. For instance, milepost A790 is on the main line in Orlando, Florida, 1000 miles south of the beginning in Richmond, Virginia, and milepost AN587 is