Lewis acids and bases factors, in addition to electron configuration factors, play a role in determining the strength of the interaction between the bulky di-"t"-butylpyridine and tiny proton. Lewis acids and bases A Lewis acid is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any species that has a filled orbital containing an electron pair which is not involved in bonding but may form a dative bond with a Lewis acid to form a Lewis adduct. For example, NH is a Lewis
Magic cube classes Perfect magic cube. Nasik; A. H. Frost (1866) referred to all but the simple magic cube as Nasik!<br> C. Planck (1905) redefined "Nasik" to mean magic hypercubes of any order or dimension in which all possible lines summed correctly.<br> i.e. Nasik is a preferred alternate, and less ambiguous term for the "perfect" class.<br>Minimum correct summations required = 13"m". All pan-"r"-agonals sum correctly for "r" = 1, 2 and 3. Alternate Perfect Note that the above is a relatively new definition of "perfect". Until about 1995 there was much confusion about what constituted a "perfect" magic cube (see the discussion under