Dangling bonds can be produced with atomic precision by selectively removing hydrogen atoms from a Si passivated surface with a scanning tunneling microscope (STM). Dangling bond wires (DBW) and dangling bond loops open fascinating possibilities for becoming the building bocks of novel planar, atomic-scale electronic circuits and logic elements. We perform a realistic study of transport properties of the DBW connected to the carbon nanoribbon leads and quantum interference effects in DBW loops by combining density-functional based approaches with equilibrium and non-equilibrium Green function methods. We develop methodology to study different topologies (half row, full row, zigzag), length of the loops, lead coupling strength and position.