Hartree-Fock calculations of the three leading coefficients in the MacLaurin expansion, Eq. (5.40), have been made [187,232] for all atoms in the periodic table. The calculations [187] showed that 93% of rio(O) comes from the outermost s orbital, and that IIo(O) behaves as a measure of atomic size. Similarly, 95% of IIq(O) comes from the outermost s and p orbitals. The sign of IIq(O) depends on the relative number of electrons in the outermost s and p orbitals, which make negative and positive contributions, respectively. Clearly, the coefficients of the MacLaurin expansion are excellent probes of the valence orbitals. The curvature riQ(O) is a surprisingly powerful predictor of the global behavior of IIo(p). A positive IIq(O) indicates a type 11 momentum density, whereas a negative rio(O) indicates that IIo(O) is of either type 1 or 111 [187,230]. MacDougall has speculated on the connection between IIq(O) and superconductivity [233]. [Pg.329]

HBr + H- H- + Br2 — HBr + Br. properties The characteristics of matter Examples vapor pressure color density temperature, protective oxide An oxide that protects a metal from oxidation. Example aluminum oxide, proton p A positively charged subatomic particle found in the nucleus of an atom, protonation Proton transfer to a Bronsted base. Example 2 H30+(aq) + S2-(s) — ... [Pg.1044]

It can be shown that (3x/3T)P = (a positive number) A7/ ) for all reactions. In the present example, AH° is positive (i.e., the reaction is endothermic). Therefore, an increase in temperature will increase x and, thus, the conversion to hydrogen and oxygen. [Pg.134]

Method of Undetermined Coefficients If Q x) is a product or linear combination of products of the functions a , x p a positive integer or zero) cos cx and sin cx, this method may be used. The "families [a ], [e " ], [sin cx, cos cx] and [x, xf, . .., x, 1] are defined for each of the above functions in the following way The family of a term f is the set of all functions of whichand all operations of the form cos c x + y), sin c x + y), (x + yf onf and their linear combinations result in. The technique involves the following steps (1) Solve the homogeneous system. (2) Construct the family of each term. (3) If the family has no representative in the homogeneous solution, assume i/J is a linear combination of the families of each term and determine the constants so that the equation is satisfied. (4) If a family has a representative in the homogeneous solution, multiply each member of the family by the smallest integral power of x for which all such representatives are removed and revert to step 3. [Pg.287]

The two other decay processes in Table 5.4 are less common in nature. In K-capture, any orbiting electron (usually in an inner shell) combines with a proton in the nucleus to form a neutron. This relatively rare nuclear transformation process (e + p+ —> n°) is just the opposite of that for P decay, meaning that the formed nucleus also has the same mass but is displaced one element to the left on the periodic table. Conversion of to °Ar by K-capture is an example of the chemical conversion that can attend radioactive decay, in this case leading to transformation of a non-volatile alkali metal into the inert gas Ar, the third most abundant gas in the atmosphere. Although no nuclear particle is emitted by K-capture, the attending cascade of electrons into lower orbitals leads to X-ray emission of characteristic energy that can be measured by the appropriate detectors. The last decay process (also rare) involves emission of a positron (p+), a positively charged electron. The nuclear process (p+ n° + p+) has the same net effect as K-capture and is also characterized by X-ray emission. [Pg.154]

Any change taking place which results in an increase in entropy has a positive entropy change (AS). Most spontaneous thermodynamic processes are accompanied by an increase in entropy. Entropy has units of Joules per degree K per mole. For representative values see table on p. 393. [Pg.158]

We are now in a position to calculate the reflections from multiple mterfaces using the simple example of a thin film of material of thickness d with refractive index n.2 sandwiched between a material of refractive index (where this is generally air witii n = ) deposited onto a substrate of refractive index [35, 36], This is depicted in figure Bl.26.9. The resulting reflectivities for p- and s-polarized light respectively are given by ... [Pg.1883]

Note that since A < 0, a p is a positive quantity. Note also tliat at far detunings equation (Cl.4.11) shows... [Pg.2465]

The quantum internal energy (fi /2m )(VY ) /p depends also on the derivative of the density, unlike in the fluid case, in which internal energy is a function of the mass density only. However, in both cases the internal energy is a positive quantity. [Pg.162]

To return to the simple picture of vertical excitation, the question remains as to how a wavepacket can be simulated using classical trajectories A classical ensemble can be specified by its distribution in phase space, Pd(p,Q), which gives the probability of finding the system of particles with momentum p and position q. In conUast, it is strictly impossible to assign simultaneously a position and momentum to a quantum particle. [Pg.270]

Adopting the view that any theory of aromaticity is also a theory of pericyclic reactions [19], we are now in a position to discuss pericyclic reactions in terms of phase change. Two reaction types are distinguished those that preserve the phase of the total electi onic wave-function - these are phase preserving reactions (p-type), and those in which the phase is inverted - these are phase inverting reactions (i-type). The fomier have an aromatic transition state, and the latter an antiaromatic one. The results of [28] may be applied to these systems. In distinction with the cyclic polyenes, the two basis wave functions need not be equivalent. The wave function of the reactants R) and the products P), respectively, can be used. The electronic wave function of the transition state may be represented by a linear combination of the electronic wave functions of the reactant and the product. Of the two possible combinations, the in-phase one [Eq. (11)] is phase preserving (p-type), while the out-of-phase one [Eq. (12)], is i-type (phase inverting), compare Eqs. (6) and (7). Normalization constants are assumed in both equations ... [Pg.343]

positive probe charge. is the n IIclear charge on atom A located at position The function p(r ) IS the electronic density. In the above equation, the first term represen ts the con tribii tion of tli e n nclei to the electrostatic poten tial and the second term is the electronic con tribiition. Siibstitii ting the electron density expression ... [Pg.245]

Acetaldehyde (and other aldehydes containing at least one hydrogen atom in the a position) when treated with a small quantity of dilute sodium hydr oxide solution or other basic catalyst gives a good yield of aldol (p hydroxy-n-but3Taldehyde) (I), which readily loses water, either by heating the isolated aldol alone or with a trace of mineral acid, to form crotonaldehyde (II) ... [Pg.351]

A particle moving with momentum p at a position r relative to some coordinate origin has so-called orbital angular momentum equal to L = r x p. The three components of this angular momentum vector in a cartesian coordinate system located at the origin mentioned above are given in terms of the cartesian coordinates of r and p as follows ... [Pg.617]

The fact that good correlations are observed with d" rather than with a, is indicative of a strong infiuence of the substituent through a direct resonance interaction with a positive charge in the reacting system. The p-values are positive, which is expected for substituted dienophiles in a normal electron demand Diels-Alder reaction. Furthermore, the p-values do not exceed unity and are not significantly different from literature values reported for the uncatalysed reaction. It is tempting to... [Pg.55]

In a second attempt to extend the scope of Lewis-acid catalysis of Diels-Alder reactions in water, we have used the Mannich reaction to convert a ketone-activated monodentate dienophile into a potentially chelating p-amino ketone. The Mannich reaction seemed ideally suited for the purpose of introducing a second coordination site on a temporary basis. This reaction adds a strongly Lewis-basic amino functionality on a position p to the ketone. Moreover, the Mannich reaction is usually a reversible process, which should allow removal of the auxiliary after the reaction. Furthermore, the reaction is compatible with the use of an aqueous medium. Some Mannich reactions have even been reported to benefit from the use of water ". Finally, Lewis-acid catalysis of Mannich-type reactions in mixtures of organic solvents and water has been reported ". Hence, if both addition of the auxiliary and the subsequent Diels-Alder reaction benefit from Lewis-acid catalysis, the possibility arises of merging these steps into a one-pot procedure. [Pg.114]

Streitwieser pointed out that the eorrelation whieh exists between relative rates of reaetion in deuterodeprotonation, nitration, and ehlorination, and equilibrium eonstants for protonation in hydrofluorie aeid amongst polynuelear hydroearbons (ef. 6.2.3) constitutes a relationship of the Hammett type. The standard reaetion is here the protonation equilibrium (for whieh p is unity by definition). For eon-venience he seleeted the i-position of naphthalene, rather than a position in benzene as the referenee position (for whieh o is zero by definition), and by this means was able to evaluate /) -values for the substitutions mentioned, and cr -values for positions in a number of hydroearbons. The p -values (for protonation equilibria, i for deuterodeprotonation, 0-47 for nitration, 0-26 and for ehlorination, 0-64) are taken to indieate how elosely the transition states of these reaetions resemble a cr-eomplex. [Pg.138]

© 2019 chempedia.info