  We review and discuss insights on ideal magnetohydrodynamic (MHD)
instabilities that can play a role in destabilizing solar coronal flux rope
structures. For single flux ropes, failed or actual eruptions may result from
internal or external kink evolutions, or from torus unstable configurations. We
highlight recent findings from 3D magnetic field reconstructions and
simulations where kink and torus instabilities play a prominent role.
  For interacting current systems, we critically discuss different routes to
coronal dynamics and global eruptions, due to current channel coalescence or to
tilt-kink scenarios. These scenarios involve the presence of two nearby current
channels and are clearly distinct from the popular kink or torus instability.
Since the solar corona is pervaded with myriads of magnetic loops -- creating
interacting flux ropes typified by parallel or antiparallel current channels as
exemplified in various recent observational studies -- coalescence or tilt-kink
evolutions must be very common for destabilizing adjacent flux rope systems.
Since they also evolve on ideal MHD timescales, they may well drive many
sympathetic eruptions witnessed in the solar corona. Moreover, they necessarily
lead to thin current sheets that are liable to reconnection. We review findings
from 2D and 3D MHD simulations for tilt and coalescence evolutions, as well as
on particle acceleration aspects derived from computed charged particle motions
in tilt-kink disruptions and coalescing flux ropes. The latter were recently
studied in two-way coupled kinetic-fluid models, where the complete phase-space
information of reconnection is incorporated.
