The Design of “Neutral” Carbanions with Intramolecular Charge Compensation

Abstract

Strategies to construct zwitterionic anions from the parent anions are proposed. Two principles are employed; the cationic counterpart is (a) attached as a substituent or (b) inserted as an integral part at a remote location in the assembly. The optimized geometries reveal that a striking similarity exists between the zwitterions and the respective precursor parent anion. The computed vibrational frequencies emphasize that these novel entities are minima on their respective potential energy surfaces. A substantial HOMO-LUMO gap indicates that the proposed structures do not show instability in their respective electronic states and that the higher energy configuration states do not contribute to the ground state viability. The separation of charge between the monopoles in these zwitterions is demonstrated by moderately large nonzero dipole moments. Significant large energy barriers for rearrangement to the closely related positional isomers, demonstrated in a few cases, advocate the thermal stability (associated with spectroscopic viability) of the novel molecules. The donor capacity (basicity) of the anionic subunit in these zwitterions is comparable to that of the respective parent anions. Since the qualitative and quantitative features in the designed charged compensated complexes are conserved as anions, these molecules may perhaps be employed in synthetic organic or organometallic chemistry.

Small Janus dimer as electric field manipulated molecular clam switch and electric information storage unit

“…Note that some Janus molecules with HOMO−LUMO gap values in the range of 1.8‐5.8 eV do not show structural instability . The studied Janus molecule is relatively stable because it possesses a larger gap value of 5.871 eV.…”

“…From Figure A, the Janus molecule, containing two electron‐withdrawing groups (2O) and two electron‐donating substitutes (2NH 2 ) on opposites sides of the phenyl ring, has a large dipole moment of 8.549 D. For the molecular structure, the bond length of 1.205 Å between C and O is close to 1.230 Å (1.242 Å) in 1,3‐daysiquinonyl‐4,6‐diaminobenzene, which means that the CO group is a carbonyl.…”

“…Note that some Janus molecules with HOMO−LUMO gap values in the range of 1.8-5.8 eV do not show structural instability. [58] The studied Janus molecule is relatively stable because it possesses a larger gap value of 5.871 eV. The electronic stability of a molecule may be characterized by its vertical ionization potential (VIP) value.…”

A Zwitterionic, 10 π Aromatic Hemisphere

“…Another aspect of 10 worth remarking on is its zwitterionic nature. Wannere and co‐workers recently published a computational study of the use of ammonium groups to charge compensate a variety of carbanions, including aromatics, leading to stabilized systems that were predicted to be isolable . Experimental examples often involve additional stabilization of the negative charge, either inductively or by conjugation to electron‐withdrawing groups.…”

A Zwitterionic, 10 π Aromatic Hemisphere

“…Another aspect of 10 worth remarking on is its zwitterionic nature.W annere and co-workers recently published acomputational study of the use of ammonium groups to charge compensate av ariety of carbanions,i ncluding aromatics,leading to stabilized systems that were predicted to be isolable. [22] Experimental examples often involve additional stabilization of the negative charge,e ither inductively or by conjugation to electron-withdrawing groups.W hile no attempt to stabilize cyclononatetraenide 6 in this way has been described, substitution of atrimethylamino group at the 9-position of fluorene only leads to adrop in pK a from 22.6 in the parent hydrocarbon to 17.8 in the ammonium salt. [23] While 6 can be quenched with H 2 O, [9a] zwitterion 10 persists even in acetic acid, although it can be protonated by MeSO 3 H to the conjugate acid 16,w hich places its pK a at < 4.…”