O-acceptors

Ho G, Heath JR, Kontratenko M, Perepichka DF, Arseneault K, Pezolet M, Bryce MR (2005) The first studies of a tetrathiafulvalene-o-acceptor molecular rectifier. Chem Eur J 11 2914-2922... 

The reasoning applied above to 0 0 interactions can be extended to weak C-H 0 bonds. The presence of a short C-H 0 distance is not necessarily indicative of an overall attractive interaction, if the C-H donor and the O acceptor groups belong to anions, as illustrated in the following example. The structure of the mixed-valent species [(ri6-C6H6)2Cr] + [Cr03(0CH3)] [34] is based on columns of methoxychromate anions and of columns of bis-benzene chromium... 

This book focuses on species of the type (RX)-, that is, on cation- and anion-radicals. These terms were first introduced by Weitz (1928) ( Kationradikale and Anionradikale ). Currently, organic chemists differentiate that the anion-radicals originate from n and o acceptors and the cation-radicals originate from n, a, or n donors. These species are formed during reactions, when an organic molecule either loses one electron from the action of an electron acceptor or acquires one from the action of an electron donor R—X - e —> (R—X)+ or R—X + e —> (R—X). ... 

Hughbanks has calculated the molecular orbitals of a hypothetical 25-e [Mo6S8L5] cluster and discussed their dimerization (72). The 2eg and 2tIu o--acceptor orbitals lie above the manifold of 12 metal-metal bonding orbitals, which include some s and p hybridization acting to accentuate their projection outward from the cluster. These orbitals are strongly destabilized when the cluster is capped by donor ligands to form the dative exo M—X bonds. There remains one 2e (z2) acceptor... 

Major hydrogen-bond donor and acceptor groups found in proteins. Note that the angle between the O acceptor and the N—H donor is 180° in the hydrogen-bond complex. 

Figure 21. Effects of neighbor groups on N(6)H2 acidity of N1,N7 diplatinated adenine Low pA"a by efficient hydrogen bonding between —NH2 donor and —NH versus high pA"a due to repulsion between —NH and O acceptor.

Two colorimetric methods have been developed which were based on the charge transfer complexation reaction of pantoprazole sodium (acting as a n-donor) with either a 7t-acceptor (such as 2, 3-dichloro-5,6-dicyano-l,4-benzoquinone, or DDQ) or with a o-acceptor (such as iodine). 

A cation (or other electrophile) will interact principally with the HOMO of the carbonyl, i.e. the oxygen p lone pair. Hence, if all other interactions are negligible, the optimum geometry for the ate complex should be 17. However, ab initio calculations13 predict structures 18 (if M+ = H+ or Me+) and 19 (if M+ = Li+ or BH2+), where the cation complexes the two lone pairs simultaneously. The bent structure 18 is favored if the Lewis acid has a o acceptor orbital, whereas the linear complex 19 is preferred if an additional rc-type acceptor orbital is available. The HOMO-LUMO interaction is slightly diminished, but this is compensated by the interaction with the s lone pair. 

When two functional groups are borne by the same atom, they interact to cause either stabilization or destabilization. This is the geminal effect.20 If the substituents are both strong o-acceptors and n-donors [for example a gem-dimethoxy-C(OMe)2-], a stabilization occurs.21 This is easy to understand. Oxygen, being electronegative, is a o-acceptor and o co is low in energy and is 71-donor thanks to its lone pair. Therefore, we have here a double anomeric effect ... 

The reaction of diazo compounds with aldehydes is catalyzed by methylrhenium trioxide and in the presence of PR3 (R = Bu, Ph) as O-acceptor leads to the formation of alkenes 100... 

In addition to the difference in the energetics of their o acceptor orbitals, S and O differ as well in the nature of their occupied orbitals. The ionization potential (IP) of the S 3p orbital is less than that of the O 2p (10.4 eV versus 13.6 eV), and its electron affinity (EA) is larger (2.1 eV... 

As it appears that the pool of electrons in the triple bond is not adequate to accept a proton from acetylene, perhaps a more conventional acceptor might be successful. Various N and O acceptors were paired with an acetylene derivative in an argon matrix and monitored... 

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