What you are about to read may be a very mind-boggling paragraph but please do not regard it as nonsense. Please think through it thoroughly.
In Chapter 6 of Organic Chemistry (4th ed.) by Maitland Jones Jr. and Steven A. Fleming, the following is written (p. 237):
In 1970, Professor John Brauman (b. 1937) and his co-workers at Stanford university showed that in the gas phase the opposite acidity order obtained. The intrinsic acidity of the four alcohols of Table 6.6 is exactly opposite to that found in solution. The acidity order measured in solution reflects a powerful effect of the solvent, not the natural acidities of the alcohols themselves. Organic ions are almost all unstable species, and the formation of the alkoxide anions depends critically on how easy it is to stabilize them through interaction with solvent molecules, a process called solvation. tert-Butyl alcohol is a weaker acid in solution than methyl alcohol because the large tert-butyl alkoxide ion is difficult to solvate. The more alkyl groups, the more difficult it is for the stabilizing solvent molecules to approach (Fig. 6.22). Of course, in the gas phase where solvation is impossible, the natural acidity order is observed.
Let me provide some context. The author is discussing the acidity of alcohols in the gas phase and in the aqueous phase. In Table 6.6 as shown above, the pKa values are provided to show the decreasing acidity of the alcohols as the alkyl portion increases in size. The author explains this by saying that it is not really due to the electron-donating effect of the alkyl groups, concentrating the negative charge on the oxygen atom. Rather, he argues that it is due to the decreased extent of solvation due to the steric hindrance provided by the bulkiness of the alkyl groups. This is a reasonable rationalisation.
However, the authors then go on to discuss the acidity of the alcohols in the gas phase and mention that the acidity trend is reversed in this situation. The alkyl groups now increase the acidity of the alcohol, rather than decrease it. The authors then state that it is due to the electron-withdrawing nature of the alkyl substituents. They even provide a qualitative molecular orbital picture of this "electron-withdrawing" interaction, as shown in the following paragraph (p. 238):
Alkyl groups have both filled and empty molecular orbitals (see the problems at the end of Chapter 1 for several examples). A pair of electrons adjacent to an alkyl group can be stabilized through overlap with the LUMO of the alkyl group. (Similarly, an alkyl group stabilizes an adjacent empty orbital through overlap with the alkyl HOMO.)
I would like to ask if anyone has ever heard of such an unconventional rationalisation and whether there is a sound theoretical basis for the postulations made above by the authors. If the postulations are indeed inconsistent with current chemical understanding, please provide a clear response detailing the areas of conflict.