Electron localization function (ELF) theory is used to characterize lone pa
irs in a variety of situations. Using the lone pair basin attractor locatio
ns, lone pair distances from their parent nucleus may be defined as well as
the angular disposition of the lone pair with regard to its neighboring at
oms and bond basin centers. Studies of the first and second row hydrides sh
ow, with some exceptions, that lone Fairs are basically tetrahedrally dispo
sed with distances dependent essentially only on the atomic number (Z) of t
he heavy atom, decreasing with increasing Z. The examination of three-to-si
x membered heterorings involving nitrogen and phosphorus show that only in
the most constrained systems are large effects noticeable. Two relatively w
eak hydrogen bonding systems (HOH . . . OH2 and FH . . . NH3) show that onl
y a very small transfer of charge occurs upon dimer formation and involves
mainly the proton donor and the acceptor lone pair; in the water dimer it i
s shown that both the acceptor lone pair and the donor proton lie off the l
ine connecting the two oxygen atoms. Finally, examination of several model
gauche and anti isomers containing ether oxygens shows that in the more sta
ble gauche form a small but noticeable transfer of charge occurs from the i
nteracting lone Fair to the adjoining carbon bonding basin, a result consis
tent with the generally accepted double-bond/no-bond sigma* orbital interac
tion model of the anomeric effect in organic stereochemistry.