  We examine the structural properties of free standing II-VI and III-V
semiconductors at the monolayer limit within first principle density functional
theory calculations. A non-polar buckled structure was found to be favoured
over a polar buckled structure. While an obvious reason for this may be traced
to the contribution from dipole dipole interactions present in the polar
structure which would destabilize it with respect to the nonpolar structure,
Coulomb interactions between electrons on the cations and anions are found to
be the reason for the nonpolar structure to be favoured. A route to tune the
Coulomb interaction between the electrons on the cations and anions is through
biaxial tensile strain. This allows for a planar graphitic phase in CdS to be
stabilized at just 2\% tensile strain. Strain also shifts the valence band
maximum from the $\Gamma$ point to the K point opening up opportunities for
exploring spin-valley physics in these materials.
