Here we studied the reactions between various 1,4-naphthoquinones and alkanedithiols, namely, 1,2-ethanedithiol and 1,3-propanedithiol. The 1,4-naphthoquinone derivatives examined were 2-bromo-, 2,3-dibromo-, 2-chloro-, 2,3-dichloro, 2-bromo-3-methoxy-, 2-methoxy-1,4-naphthoquinone and 1,4 naphthoquinone itself. All of these 1,4-naphthoquinones are potentially expected to go through substitution reactions. We identified two groups of substitution products. In the reactions with 1,2-ehtanedithiol, for example, a ?cyclic product?, 2,3-dihydro-1,4-dithia-9,10-anthracenedione, and a ?spiro product?, 2-1?,3?-dithiacyclopentane spiro 2?-2,3-dihydro-1,4-naphthoquinone or its 3-halogeno-derivative. The formation of these two groups of products, a ?cyclic product? and a ?spiro product,? were found to depend upon the substituents on the 2- and/or 3-positions of 1,4-naphthoquinones as well as the reaction medium, be it acidic, neutral, or basic. This observation strongly indicates that different mechanisms are involved in the substitution reactions.