  Although many graphene derivatives have sizable band gaps, their electrical
or mechanical properties are significantly degraded due to the low degree of
{\pi}-conjugation. Besides the {\pi}-{\pi} conjugation, there exists
hyperconjugation interactions arising from the delocalization of {\sigma}
electrons. Inspired by the structural characteristics of a hyperconjugated
molecule, dimethyl ether, we design a two-dimensional oxocarbon (named
graphether) by the assembly of dimethyl ether molecules. Our first-principle
calculations reveal the following findings: (1) Monolayer graphether possesses
excellent dynamical and thermal stabilities as demonstrated by its favourable
cohesive energy, absence of the soft phonon modes, and high melting point. (2)
It has a direct wide-band-gap of 2.39 eV, indicating its potential applications
in ultraviolet optoelectronic devices. Interestingly, the direct band gap
feature is rather robust against the external strains (-10% to 10%) and
stacking configurations. (3) Due to the hyperconjugative effect, graphether has
the high intrinsic electron mobility. More importantly, its in-plane stiffness
(459.8 N m-1) is even larger than that of graphene. (4) The Pt(100) surface
exhibits high catalytic activity for the dehydrogenation of dimethyl ether. The
electrostatic repulsion serves as a driving force for the rotation and
coalescence of two dehydrogenated precursors, which is favourable for the
bottom-up growth of graphether. (5) Replacement of the C-C bond with an
isoelectronic B-N bond can generate a stable Pmn21-BNO monolayer. Compared with
monolayer hexagonal boron nitride, Pmn21-BNO has a moderate direct band gap
(3.32 eV) and better mechanical property along the armchair direction.
