Actual Symmetry of Symmetric Molecular Adducts in the Gas Phase, Solution and in the Solid State

Abstract

This review discusses molecular adducts, whose composition allows a symmetric structure. Such adducts are popular model systems, as they are useful for analyzing the effect of structure on the property selected for study since they allow one to reduce the number of parameters. The main objectives of this discussion are to evaluate the influence of the surroundings on the symmetry of these adducts, steric hindrances within the adducts, competition between different noncovalent interactions responsible for stabilizing the adducts, and experimental methods that can be used to study the symmetry at different time scales. This review considers the following central binding units: hydrogen (proton), halogen (anion), metal (cation), water (hydrogen peroxide).

Loss of CO2 from Monodeprotonated Phthalic Acid upon Photodissociation and Dissociative Electron Detachment

“…Photodetachment and Anionic Excited State Energy Calculations. In accordance with previous work on HPA − , 16 our calculations confirmed that the ground state geometry of the monoanion is planar, with any nonplanar geometry converging toward the planar one. In the lowest energy geometry, the acidic H atom is located in the middle of two O atoms belonging to different carboxylic groups each (see Figure 4), forming an O•••H•••O Zundel-type bond with C 2v symmetry.…”

“…In the case of symmetrical vicinal dicarboxylic monoanions (ortho isomers), there is an additional topic of interest concerning the location of the hydrogen atom in the intramolecular H-bond that is established between the two (equivalent) carboxylic groups. 16 A representative model system to study the symmetry of such an intramolecular Hbond is the monodeprotonated phthalic acid (HPA − , that may also be referred to as benzenedicarboxylic monoanion). In the gas phase, the intramolecular H-bond in HPA − is symmetric and hence the negative charge is equally delocalized over the two carboxylic groups.…”

“…The presence of a second carboxylic group in the aryl structure alters the excitation energy profile of the anion, and it is likely to change the fragmentation dynamics as well. In the case of symmetrical vicinal dicarboxylic monoanions (ortho isomers), there is an additional topic of interest concerning the location of the hydrogen atom in the intramolecular H-bond that is established between the two (equivalent) carboxylic groups . A representative model system to study the symmetry of such an intramolecular H-bond is the monodeprotonated phthalic acid (HPA – , that may also be referred to as benzenedicarboxylic monoanion).…”

Modeling of the Response of Hydrogen Bond Properties on an External Electric Field: Geometry, NMR Chemical Shift, Spin-Spin Scalar Coupling

“…They agree with dependences obtained for other experimental and empirical parameters [18][19][20][21][22]. More about the application of these and other correlations can be found elsewhere [23][24][25][26].…”

NMR Properties of the Cyanide Anion, a Quasisymmetric Two-Faced Hydrogen Bonding Acceptor

“…The N≡C and C•••H distances are very short. [101,102] and recently reviewed [103]. In [CN] − •••H-CN, the hydrogen bond is stronger, and the position of the proton is more symmetric.…”