Oxygen lone-pair electrons

UV-VIS Aldehydes and ketones have two absorption bands in the ultraviolet region Both involve excitation of an electron to an antibonding tt orbital In one called a TT TT transition the electron is one of the tt electrons of the C=0 group In the other called an n ir transition it is one of the oxygen lone pair electrons Because the tt electrons are more strongly held than the lone parr electrons the transition is of... 

G. activates the carbonyl group for nucleophilic attack by oxygen lone-pair electrons from the alcohol. 

The ligand properties of a cyclic dithioether, 1,4-dithiane monosulphoxide (DTMSO), have been studied by physical measurements . The infrared spectra indicate that the metal cation coordinates to the oxygen lone pair electrons of DTMSO. Both infrared and ligand-field spectra show the presence of octahedral ions MfDTMSO) in the compounds M(DTMS0)g(C104) and M(DTMSO)g(BF4) . In the case of M = Cu these ions are distorted from the regular octahedral structure. 

Computer simulation of lanthanide-induced shifts in the 2-formyl and 2-acetyl derivatives of furan, thiophene, selenophene, and tellurophene108 indicate a nearly equipopulated mixture of trans and cis conformers of the furan, and a preponderance of the cis for the thiophene, selenophene, and tellurophene derivatives. This difference is due to an interaction between the ring heteroatom and the carbonyl oxygen lone pair electrons. 

The driving force for growth of the crystal in the b direction is the energy released by formation of the NH O bonds of the ribbon motif. E-Cinnamic acid in the stable synplanar conformation 2a can replace a E-cinnamide molecule at the end of the ribbon however, at the site of the additive, the attractive NH O bond (- 6 kcal/mol) is replaced by repulsion between the adjacent oxygen lone-pair electrons of the bound additive molecule and of the oncoming cinnamide molecule (1-2 kcal/mol), which leads to an overall loss in energy of 7-8 kcal/mol at the site of the additive (Scheme 6 on page 16). 

The effect of substituent groupings upon the first ionization potential of, at least, the aliphatic aldehydes and ketones does not seem to provide clear evidence for a choice between loss of a 7r-electron from the C=0 double bond or one of the oxygen lone-pair electrons. Concordant data for the homologous series of aliphatic ketones have been obtained by... 

On the assumption that all the reported aldehyde first ionization potentials refer to the oxygen lone-pair electrons Cook (1958) has classified the effect of substituents into two classes, A and B, according to whether inductive or resonance effects predominate. Two different linear correlations (Fig. 14) were found between ionization potential and the carbonyl stretching frequency. Anomalies were noted for diacetyl, benzaldehyde and mesityl oxide, ascribed in the last instance to noncoplanarity interfering with resonance. It seems more likely, however, that in these cases the first ionization potential refers to 7r-electrons and higher values for the lone-pair electrons (as yet undetermined) might remove the anomalies. 

It appears that the heptachlor epoxide is adsorbed onto the stationary phase so that it does not expose the oxygen lone pair electrons to the polar mobile phase. Incomplete desolvation by the stationary phase can result in an error of the opposite sign. This is probably the reason the log P(oct) of tricresyl phosphate by HPLC is reported as 3.42 (Veith, 1979), while it is calculated to be about 6.0 (CLOGP = 5.95 ACD = 6.23 KOWWIN = 6.34). 

The activation of the nitronium ion (212, N02+) can be understood as a consequence of the interaction of the oxygen lone pair electrons... 

Conjugation with the oxygen lone pair electrons makes the double bond more nucleophilic. 

Isolation and identification of surface-bonded acetone enolate on Ni(l 11) surfaces show that metal enolate complexes are key intermediates in carbon-carbon bond-forming reactions in both organometaUic chemistry and heterogeneous catalysis. Based on studies on powdered samples of defined surface structure and composition, most of the results were reported for acetone condensation over transition-metal oxide catalysts, as surface intermediate in industrially important processes. With the exception of a preoxidized silver surface, all other metal single-crystal surfaces have suggested that the main adsorption occurs via oxygen lone-pair electrons or di-a bonding of both the carbonyl C and O atoms. 

Experimental studies as well as theoretical calculations indicate that hydrogen bonds are strengthened when water molecules act as both proton donor and proton acceptor ( cooperative effect ). Thus, an H2O molecule bonded to another H2O via oxygen lone-pair electrons behaves as a stronger acid than an isolated H20 . ... 

Some insight into these interactions may be obtained from the distribution of oxygen lone-pair electrons calculated by the ab initio method with... 

Some time later, Rob Guy, whose chemical skills were much respected by the research team and who was also envied for his ability to charm ladies, managed to synthesise a range of acetylene complexes of platinum. Their infrared spectra indicated that bonding of the hydrocarbon to the metal was very similar to that in olefin complexes. Interestingly, it was observed that a-hydroxyacetylenes are chelated to platinum through interaction of oxygen lone-pair electrons with a vacant 6p orbital of the metal. 

Novel photochemical (and thermal) reactions of macrocyclic oxa-sila-acetylenic ring systems (expected to show unusual optical properties because of electronic effects arising from orbital overlap of the acetylenic n system with the silicon a bonds and the oxygen lone-pair electrons) were described. While thermolysis in the presence of a transition metal carbonyl compound gave cyclization to both benzenoid and fulvene species, photolysis in the presence of the transition metal carbonyl compound (which catalyzes 1,2-silyl shifts across a carbon-carbon triple bond) gave fulvene and vinylidene products, the latter being readily photolyzed to the fulvene 159 (equation 101). 

Electrostatic interactions with the oxygen lone-pair electrons are not, exclusively, the sole cause of the anomeric effect. Increasing the positive charge on C5 by substitution with electronegative groups increases the strength of the dipole and hence the anomeric effect (Fig. 3) [18]. 

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