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known x* •*n transitions are blue shift, but that the converse is not necessarily true, quoting the case of the v* *-2600 A. transition of benzene, which is blue shift in his terminology. Now the case of benzene has been shown definitely by Bayliss and Hulme9 to be a polarization red shift (cases I and II), and in fact all polarization red shifts are "blue" shifts in McConnell's sense, since the refractive indices decrease in the order paraffin, alcohol, water. McConnell's definition fails to make the important distinction between (a) "blue shifts" that are red shifts compared with the gas as in cases I and II, and (b) "blue shifts" that are blue • shifts compared with the gas as in cases Ilia and IVa.However it is readily seen that a * +-n transi-tion is likely always to conform to cases Illa and IVa, since it involves a non-bonding (n) electron localized on a hetero-atom which is usually exposed or terminal to a conjugated system. During the transition it is excited into a x* orbital associated with a neighboring double bond or with a non-localized conjugated system. There is thus an electron displacement away from the hetero-atom, and this will usually decrease the dipole moment or the H-bonding capacity. The cases of acetone, crotonaldehyde, nitromethane and nitrobenzene are instructive in this regard, and are described in the following paper.7

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