Naphthalene tetrachlorides and related compounds. Part IV. Photochemical chlorination of 1-chloronaphthalene

The photochemical chlorination of 1-chloronaphthalene gives a mixture of dichlorides, which on further chlorination give several new 1-chloronaphthalene tetrachlorides. The structures of the latter have been elucidated by using 1H n.m.r. spectroscopy and by isomerisation with aluminium trichloride as the 1,1,r-2,t-3,c-4- and 1,1,r-2,-c-3,t-4-pentachlorotetralins; and the r-1,t-2,t-3,c-4,5-; r-1,t-2,c-3,c-4,5-; and r-1,t-2,c-3,t-4,5-pentachlorotetralins. Evidence is presented to suggest that the last compound, because of internal non-bonding strain, exists predominantly in an unusual ‘half-boat’ conformation. The results are compared with those obtained by heterocyclic chlorination, from which another isomer, r-1,c-2,t-3,t-4,5-pentachlorotetralin, is a minor product. The course and products of alkaline dehydrochlorination have been used to support some of the assignments of structure. The heterolytic chlorination of 1,2-dichloronaphthalene has been examined also; the major product is r-1,t-2,c-3,t-4,5,6-hexachlorotetralin, which also exists in a ‘half-boat’ conformation.