Atom controlled

What Are the Key Ideas Bond formation is accompanied by a lowering of energy. That lowering of energy is due to the attractions between oppositely charged ions or between nuclei and shared electron pairs. The electron configurations of individual atoms control how the atoms combine with one another. 

Just as valence-shell electrons rather than core electrons are the most easily lost during ionization, they are also the most easily lost or shared during chemical reactions. We ll see repeatedly in later chapters that the valence-shell electron configuration of an atom controls the atom s chemistry. 

To explain the regioselectivity trend in the photo-oxygenation of allylic silanes, it was proposed that an interaction between the negatively charged oxygen of the perepoxide and the silicon atom controls the abstraction of allylic hydrogen atoms (Scheme 20). The formation of cis ene adducts [86] was attributed either to the intermediacy of a zwitterionic intermediate or to a nonconcerted pathway. A perepoxide intermediate was considered unlikely. 

Macroscopic control of bonding. . . Atomic control of bonding... 

See also the main entry -+ underpotential deposition. Refs. [i] Haissinsky M (1933) J Chim Phys 30 27 [ii] Frumkin AN (1934) Zh Fiz Khimii 5 240 [iii] Kolb DM (1978) Physical and electrochemical properties of metal monolayers on metallic substrates. In Gerischer H, Tobias CW (eds) Advances in electrochemistry and electrochemical engineering, vol. 11. Wiley New York, p 125 [iv] Conway B (1984) Progr Surf Sci 16 1 [v] Ye S, Uosaki K (2003) Atomically controlled electrochemical deposition and dissolution of noble metals. In BardAJ, Stratmannn M, Gileadi E, Urbakh M (eds) Thermodynamics and electrified interfaces. Encyclopedia of electrochemistry, vol. 1. Wiley-VCH, p 471 [vi] Adzic R (2003) Electrocatalysis on surfaces modified by metal monolayers deposited at underpotentials. In Bard AJ, Stratmannn M, Gileadi E, Urbakh M (eds) Thermodynamics and electrified interfaces. Encyclopedia of electrochemistry, vol. 1. Wiley-VCH, p 561... 

The nitrogen atom, when uncombined, has 5 valence electrons. In the compound, the shared electrons are controlled by the fluorine atoms, so the nitrogen atom retains control of only the unshared pair of electrons. It controls only 2 electrons. Its oxidation state is 5 - 2 = -1-3. The uncombined fluorine atom has 7 valence electrons but in the compound, each fluorine atom controls 8, so its oxidation number is 7 - 8 = -1. 

Application of this cyclization reaction to a large variety of 4-pentenals with the aid of the rhodium complex has been reported. The first example of an asymmetric cyclization of 4-pentenals via hydro acylation using a chiral rhodium diphosphine catalyst was published by Sakaki et al. in 1989 [ 104]. The diphosphine ligand ((lS,2S)-rraws-l,2-bis(diphenylphosphinomethyl)cyclohexane) having a cyclohexane backbone in the chiral center shows the better asymmetric induction than DIOP ligand. Various types of enals are applicable to this asymmetric intramolecular hydro acylation reaction [105,106]. The use of BINAP ligand as the chiral auxiliary improves the optical yield to >99% ee when 4-substituted 4-pentenals are used as the substrate (Eq. 49) [106]. Steric repulsion between the substituent at the 4-position and the substituent on the phosphine atom controls the enantiofacial selection. 

Electronic Size Effects. Understanding the size-dependent electronic structure of the Au /MgO(Fsc) model catalysts, which is fundamental for elucidation of their atom-by-atom controlled reactivity, is facilitated by analysis of the spectra of the LDOS projected on the oxygen molecule and on the metal cluster (see also Electronic Size Effects ). Figure 1.78a shows the LDOS projected on the O2 molecule which is adsorbed at the peripheral site (Fig. 1.77f) of the more reactive isomer of the Aug/MgO(F5c) model catalyst. As shown above, bonding and activation of O2 on the octamer is enabled by resonances formed between the cluster s electronic states and the 2jt molecular states... 

When the H-atom becomes dynamically disordered in the hydrogen bond, the electronic structures of the hydrogen-bonded atoms are switched over in the rhythm of the H-hopping. The electronic structure of the H-donor and acceptor atoms controls the O-H and H- O lengths as well as the R-O-H and H-O-R angles. When the H-atom becomes disordered between the H-donor and acceptor groups, the only way to preserve these dimensions is to bend the... 

Another aspect of interest is how the oxidation state of the iron atom controls the conformational state of the polypeptide. In certain cases the electronic configuration of the ion is of fundamental importance since only one valence state can exist chelated by the polypeptide. Such appears to be the case in the siderochromes and in transferrin, where... 

The calculated photoabsorption spectrum of this cluster shows a collective excitation with a peak at 2.12 eV. The tail of the resonance extends up to 3 eV, and concentrates a sizable amount of strength, due to particle-hole transitions that interact with the collective excitation and lead to its broadening. One of the most important particle-hole transitions is that from the HOMO level to the continuum the energy of this ionization threshold is indicated by the arrow at 2.6 eV. Similar TDLDA calculations have been performed for pure Na [104] and pure K [127] clusters. Comparing the positions of the collective resonances, it can be concluded that the position of the resonance in K2oNa2o is closer to that in pure K clusters thus, the surface, made of K atoms, controls the frequency of the collective resonance. 

S. B. Sinnott, R. J. Colton, C. T. White, and D. W. Brennei Surf. Set., 316, L1055 (1994). Surface Patterning with Atomically-Controlled Chemical Forces Molecular Dynamics Simulations. 

Atomically Controlled Electrochemical Deposition and Dissolution of Noble Metals... 

Recently, in addition to the in situ STM/AFM, many other surface-analysis techniques such as surface X-ray scattering (SXS) [19, 20] and electrochemical quartz crystal microbalance (EQCM) [21, 22] have also been employed to investigate the electrochemical deposition and dissolution processes at atomic resolution. Atomically controlled electrochemical epitaxial growth and layer-by-layer dissolution... 

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