Donor quantum chemical calculations

Interactions between hydrogen-bond donor and acceptor groups in different molecules play a pivotal role in many chemical and biological problems. Hydrogen bonds can be studied with quantum chemical calculations and empirical methods. 

Cationic low-coordinated n-bonded phosphorus compoimds add Lewis donors, such as amines or phosphines. In contrast to the trigonal bipyramide formed in donor-addition to the silico-nium cation, the phosphorus cations add donors in a perpendicular fashion, depending on the nature of the n-bonds toward phosphorus. According to quantum chemical calculations the various cations reveal different stabilities and hence a strong variation in donor addition abilities. 

According to quantum chemical calculations the cations P02 and PS2 should be linear [90,91 ] while in the corresponding 2-phosphallyl cation the central phosphorus atom is reluctant to sp-hybridisation [92] and is bent. Bis-donor adducts 34-36 were reported for a variety of these cations with dimethylaminopyridine (DMAP) (Scheme 21). 

From experiments as well as from the Gutmann donor number for acetonitrile (only 50% of that for water), it is well known that addition of water to solutions of lithium ions in acetonitrile leads to the formation of a water coordinated Li+ ion. This can be reproduced for HCN as modeled by quantum chemical calculations (RB3LYP/6-311+G ). 

The isopyridine 179 (3<52-lH-pyridine) is the result if the oxygen atom of 180 is replaced by an NH group. Owing to the better electron-donor quality relative to that of an oxygen atom, the NH group could have the effect that the zwitterion 179-Zj is more stable than the allene structure 179, even in the gas phase. Experiments and quantum-chemical calculations support this expectation. 

Rosch N, Voityuk AA (2004) Quantum Chemical Calculation of Donor-Acceptor Coupling for Charge Transfer in DNA. 237 37-72 Rohovec J, see Frullano L (2002) 221 25-60... 

Quantum Chemical Calculation of Donor-Acceptor Coupling for Charge Transfer in DNA... 

The transfer rate constant of single-step CT depends on various parameters [25, 26], but the electronic couphng Vda- is crucial for the dependence of the rate constant on the distance between a donor d and an acceptor a and on their orientation. Electronic interactions of donor and acceptor with the intervening medium, in turn, determine the couphng Vda which can be found from quantum chemical calculations on pertinent models. A number of excellent reviews discussed the quantum chemical treatment of electron transfer [27-29]. 

---