However, for most of these, the resulting product is only at best metastable (e.g. diamond) when returning to ambient conditions, and does not survive when pressure returns to ambient conditions (r.t.p.).
For the following requirements, a compound that has unusual bonding similar to those 3 reported above, that is things like n centre m electron bonds is desired
Are there exceptions to this rule, where the high pressure is mainly needed to overcome the energy barrier and the resulting product is more stable than the reactants such that the product stays stable (instead of metastable) even when it is decompressed (That is, a spontaneous but kinetically slow reaction where pressure is the major factor to activate the reaction)?
If there are no known exceptions, what are possible theoretical reasons that products formed from high pressure are usually metastable and cannot survive at low pressures. Put it simply, why are most reactions reversible under the change of pressure?