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 Also, like the ACL, the SAL mainline ran from Richmond, Virginia to Tampa, Florida. The S Line is today discontinuous and segments of the original line have been abandoned (notable abandoned segments are between Chester, Virginia and Norlina, North Carolina, and between Riceboro and Seals, Georgia. The Seaboard main line from Richmond to Tampa, heart of its 2600-mile system in 1900, had been built by the following companies: 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.