The Alpha Effect was first described by William P. Jencks and Joan Carriuolo in 1960.
It refers to the increased 'nucleophilicity' of a molecule (i.e. the tendency for molecules or ions to donate a pair of electrons to form a chemical bond) due to the presence of another adjacent (alpha) atom with lone pair electrons.
The effect has been very well verified, and is routinely used.
A number of competing theories have been put forward to explain the phenomenon, but as yet there is no agreement in the international chemistry community as to the correct explanation.
Further reading at Wikipedia.