SummaryCritical micelle concentrations (CMC) are shown to depend on chain length. All straight chain saturated surface active agents of equal ion length have approximately the same CMC. Thus a C13 fatty acid soap, a C12 sulfonate, a C11 sulfate, and a C12 ammonium chloride have CMC values of 0.010–0.014M. Values of CMC are not changed to any extent by substitution near the hydrophilic head of one, two, or three groups, even as large as hydroxyethyl, in place of the amine hydrogens in the cationic detergents. However substitution with dihydroxypropyl groups has a marked effect on association in C12 but not in the C16 series, indicating that the relative lengths of the two chains must be considered as an important factor in association. This is well illustrated in the dialkylsulfosuccinate series, and in a tetradecane sulfate series in which the −SO4Na group was progressively moved down the chain, particularly when the branched chain compounds are compared with the corresponding straight chain detergents of length equal to the maximum length from the charged head to the ultimate carbon atom. Introduction of double bonds causes a small but definite increase in CMC whereas polar substitution in the chain results in a marked increase in CMC. Possible micelle structures are discussed in the light of these association phenomena, and it is concluded that the assignment of a definite size and shape to micelles appears at the present time to be slightly premature. However if one includes the concept of relative order‐disorder in the micelle as one of the factors, in addition to chain length, type of detergent, and environment, which are important in micelle structure, it is possible to explain partially the apparent marked differences which have been reported for micelles of different surface active agents.

The spectra of naphthalene, anthracene, naphthacene, phenanthrene, 1,2-benzanthrene, chrysene, and acenaphthene in n-heptane solution are extended to 1700A. Electronic energy levels of 17 such cata-condensed hydrocarbons are collected and compared. The lowest five or six excited states shift in a regular way with changes of molecular length and shape. Intensities and vibrational structures of corresponding bands are remarkably alike in the different compounds. The total oscillator strength is almost proportional to the number of π-electrons, but the proportionality constant differs from that in polyenes. With new identifications, the positions of energy levels in naphthalene, anthracene, and azulene agree remarkably well with previous LCAO molecular orbital calculations. The lowest singlet state is of one type in benzene, naphthalene, and most non-linear systems; of another type in anthracene and the higher linear polyacenes because of a cross-over. This clears up some controversial questions, such as the relations among the spectra of naphthalene, anthracene, and phenanthrene.

No abstract

No abstract

No abstract