Companies Quantum Chemical announced a restructuring plan that calls for paying a special $50-a-share dividend and selling its specialty chemical division.

Quantum Chemical fell 1 7/8, to 105 3/8, as the most active stock on the Big Board.

Quantum Chemical provided the market with some excitement, as Hanson P.L.C. reached an agreement to acquire the company.

The chemicals businesses, most of which are in the United States, include Quantum Chemicals and SCM.

Another active issue was Quantum Chemical, which rose 18 5/8 on Wednesday after announcing a restructuring plan that included a $50-a-share special dividend.

Hanson will buy Quantum Chemical in a $3.2 billion deal.

Quantum Chemical was a standout among the chemicals, rising 1 1/4, to 21 3/4, also in heavy trading.

Active Issues Quantum Chemical fell 2 3/4 points, to 77 1/2.

Among the American units that Hanson will keep are two of its biggest subsidiaries, Quantum Chemical and Peabody Coal.

Chemical Stocks Advance Some chemical stocks gained on news of an early-morning explosion at Quantum Chemical's ethylene unit.