Electron-donating substituents favour cis-addition of bromine to 4,4?- substituted (2)-stilbenes; trans-addition is favoured by electron- withdrawing substituents.

The rates of detritiation of [2-T]-, [3-T]-, and [4-T]-1,8-dimethylnaphthalene and the corresponding specifically labelled acenaphthenes and perinaphthanes have been measured a t 30° in anhydrous trifluoroacetic acid. The order of ortho and para reactivities is acenaphthene > perinaphthane > 1,8-dimethylnaphthalene; the meta positions are much less reactive in the order acenaphthene > 1,8-dimethyl- naphthalene > perinaphthane. This pattern of reactivity is discussed in terms of steric and strain effects in the transition states.

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The chemical shifts of the hydroxy-proton of 2.6-dimethyl phenol and ten 4-substituted 2.6-dimethylphenols and of I -naphthol and nine 4-substituted 1 -naphthols have been measured for dimethyl sulphoxide solutions. Analysis of published data on the chemical shifts of phenols in dimethyl sulphoxide reveals that +M as well as -M 4-substituents exhibit enhanced resonance effects. Substituent effects in 2,6-dimethylphenols and in 1 -naphthols parallel these effects in phenols. The Hammett p values for the three series are -1.49, -1.43, and -1.55 respectively. In naphthols -M 4-substituents do not exhibit enhanced resonance effects over and above those observed in the correspondingly substituted phenols.

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