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The published method had erroneous headspace calculations listed and n-butanol could not be recommended as a training odorant because of its irritancy.

now known, for example, that the increase in aqueous acidities in the CH 3 COOH-CF 3 COOH series is not primarily a result of inductive electron withdrawal by fluorine but is mainly due to entropy contributions (5). Similarly, the increasing inductive donation of methyl groups, manifested in the gas phase basicity order NH 3 < MeNH 2 < Me 2 NH < Me 3 N is not followed in aqueous solution where an inversion occurs to give the order (6) NH 3 < Me 3 N < MeNH 2 < Me 2 NH This arises because the diminished hydrogen bonding of Me 3 NH + in the aqueous phase gives a lesser stabilization. Also the more effective hydrogen bonding of water to protonated aniline, as compared with aniline, will counter the resonance stabilization of the latter. In fact aniline becomes a stronger base than ammonia in the gas phase (7). The failure of the third corollary is probably due to the steric hindrance presented by ortho-substituted anilines to protonation by hydroxonium ions.At the very least, evidence concerning geometries of anilines derived from aqueous basicities can be misleading. Also, the other type of evidence from dipole moments, derived from vector addition of bond dipoles, requires location of electron densities. This is a nonobservable, and charge distributions are to some extent arbitrary depending on the method used for partitioning electron density (8).Advances in computational programming now enable energies and geometries of isolated molecules to be routinely calculated. The energies of isomers that are unavailable experimentally can also be estimated. Thus pyramidal and planar forms of amines can be compared and the more stable form predicted. Some energy differences and geometries calculated with the simplest ab initio basis set (STO-3G) are collected in Table 2. Although total energies become more negative with larger basis sets and with correlation corrections, energy differences between closely related isomers are reliable enough to select stable forms (9). In all instances the bent pyramidal form is the more stable. The energy difference can be regarded as the energy barrier to inversion, the planar form acting as the transition state. These ab initio calculations conform with VSEPR expectations, indicating the lone pair density in nitrogen is not fully dispersed via resonance.In the more stable bent forms the C-N distances change as expected on substitution but remain constant in the planar forms. The shortening of this bond between forms averages 0.042 Å. Unexpectedly, from the resonance viewpoint, the C-N bond in the pyramidal forms is not co-A perceptive student, after becoming acquainted with VSEPR theory (1), may well query why ammonia and alkyl amines are depicted as pyramidal in organic texts whereas anilines are always drawn as planar molecules. Following Pauling (2), the difference is generally attributed to the dispersal of nitrogen lone pair density over three polar resonance forms (3)(4)(5) in the aromatic amine that are unavailable in aliphatic amines (Fig. 1). The sp 3 hybridization at nitrogen in...

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