NOVELTY - A compound (C1) comprising a group containing a radical linked to negative point charge, which is capable of being neutralized via a linker is new. The radical is not pi -conjugated to the negative point charge and the lowest Singly-Occupied Molecular Orbital (SOMO) of radical is lower in energy than in the corresponding compound when the negative point charge is neutralized.    USE - In radical protecting group to protect a radical, where the negative point charge is neutralized; for measuring the pH of a medium; in molecular electronic applications, inclusive of solar cells; in medical treatment of medical condition; in the manufacture of a medicament for the treatment and/or prevention of a medical condition (claimed); in chemical synthesis and/or in physical or chemical analysis or in sensors.    ADVANTAGE - The compound allows application of controlled and reversible switching of the Singly Occupied Molecular Orbital (SOMO) from a high energy level (e.g. the Highest Occupied Molecular Orbital (HOMO)) to a lower energy level by direct physical or chemical systems. The addition of protons (or other cations) to the compound (I) causes the radical to be 'activated' and so to become more reactive (activating the radical for reaction, e.g. for use in radical-based chemistry).    DETAILED DESCRIPTION - A compound (C1) of formula RAD-L-NEG (I) is new, where the radical of RAD is not pi -conjugated to the negative point charge of NEG and the lowest Singly-Occupied Molecular Orbital (SOMO) of RAD is lower in energy than in the corresponding compound of formula (I) when the negative point charge of NEG is neutralized.    RAD=a group comprising a radical;    NEG=negative point charge, which is capable of being neutralized;    L=linker that links NEG and RAD.    INDEPENDENT CLAIMS are included for the following:    (1) a radical protecting group (P1) having the compound (I), where the radical of RAD is capable of forming a bond to a radical to be protected to give the protected radical; and the bond to the radical to be protected is weakened when the negative point charge of NEG is not neutralized;    (2) a radical protecting group (P2) having the compound (I), where the radical of RAD is capable of forming a bond to a radical to be protected to give the protected radical, and the radical to be protected is deprotectable when the negative point charge of NEG is not neutralized;    (3) a process (M1) of de-protecting a radical protected with radical protecting group (P1) or (P2) involving the removal of the cause of neutralization from a negative point charge that has been neutralized;    (4) a process (M2) of deprotecting a radical protected with the radical protecting group (P1) or (P2) involving removal of the negative point charge; allowing the negative point charge to dissipate; or inverting the negative point charge to a positive point charge;    (5) a process (M3) of protecting a radical by reacting that radical with the radical protecting group (P1) or (P2), where the negative point charge is neutralized;    (6) process (M4) of activating the radical protecting group (P1) or (P2) by neutralizing the negative point charge;    (7) use of the radical protecting group to protect a radical, where the anion of NEG is bonded to a proton, or other cation;    (8) a process (M5) of deprotecting a radical protected with radical protecting group;    (9) a process (M6) of protecting radical involving reacting that radical with the radical protecting group, where the anion of NEG is bonded to a proton or other cation;    (10) a process (M7) of activating the radical protecting group involving addition of protons or other cations to the reaction medium, where the anion of NEG bonds to added protons or other cations; or decreasing the pH of the reaction medium, to protonate the anion of NEG;    (11) a process (M8) of deprotecting radical protected with the radical protecting group by increasing the polarity of the reaction medium, such that the protons or other cations bonded to the anion of NEG dissociate from that anion;    (12) a process (M9) of activating the radical protecting group involving decreasing the polarity of the reaction medium, such that protons or other cations in the reaction medium bond to the anion of NEG;    (13) a process (M10), where at least one of the processes (M1)-(M9) is used;    (14) a process (M11), where at least one of the processes (M1)-(M4) and (M5)-(M10) is used;    (15) a process (M12) of monitoring the pH of a medium by measuring the concentration of at least one of the protected radical, the radical be protected, or the radical protecting group; or at least one product resulting from these species;    (16) use of the radical to he protected and/or the radical protecting group as a radical scavenger;    (17) a process (M13) of oxidation of compound (I) by the removal of an electron to give a biradical species;    (18) a process (M14), where method (M13) is used;    (19) use of computational system (S1) to identify compound (I);    (20) compound identified by the system;    (21) a method (M15) of stabilizing a radical bearing structure, involving introduction of negative point charge to the compound, where the resultant structure formed is of formula (I); or incorporation of an anion into that compound, where the resultant compound formed is compound (I);    (22) resultant compound formed by the method (M15);    (23) a method (M16) of increasing the pKb of a conjugate-base bearing compound, involving incorporating a radical into the compound, where the resultant compound is of formula (I);    (24) resultant compound formed by method (M16);    (25) a method (M17) of lowering the energy level of the Singly-occupied Molecular Orbital of RAD by the removal of the cause of neutralization from a point charge of NEG that has been neutralized, in a compound (I);    (26) a method (M18) of raising the energy level of a Doubly-Occupied Molecular Orbitals of NEG above the energy level of the Singly-Occupied Molecular Orbital of RAD, by the removal of protons and/or other cations from the anion of NEC, where the compound is compound (I);    (27) a resultant compound formed by method (M18);    (28) a method (M19) of modifying a biological macromolecule;    (29) a method (M20) of modifying a biological macromolecule;    (30) a method (M21) of modifying a biological macromolecule;    (31) a method (M22) of modifying a biological macromolecule;    (32) a method (M23) of modifying a substrate such that the resultant modified substrate with form a complex with a biological macromolecule;    (33) a method (M24) of modifying a biological macromolecule and a substrate;    (34) a modified biological macromolecule and/or modified substrate formed by the method;    (35) use of a modified biological macromolecule and/or modified substrate; and    (36) a method of medical treatment of a medical condition, involving administration of compound (I).