B term

Inspection of the values for the structure elements and their contribution to the heats of formation again allows interpretation The B-terms correspond to the energies to break these bonds, and a sequence of three carbon atoms introduces stabihty into an alkane whereas the arrangement of three carbon atoms around a central carbon atom leads to the destabilization of an alkane. 

The presence of the q B term with its implied distance dependency means that the charges depend upon the molecular geometry. Thus, should the conformation of a molecule change the atomic charges will also change. Just three parameters are required for each atom in the system (the electronegativity, the idempotential and the covalent radius). 

It is interesting to note that for a van der Waals gas, the second virial coefficient equals b - a/RT, and this equals zero at the Boyle temperature. This shows that the excluded volume (the van der Waals b term) and the intermolecular attractions (the a term) cancel out at the Boyle temperature. This kind of compensation is also typical of 0 conditions. 

Fig. 1. Schematic drawing of precursors for selected brain oligopeptides. Shaded areas represent the location of sequences of active peptide products which are normally cleaved by trypsin-like enzymes acting on double-basic amino acid residues. Precursors are not necessarily drawn to scale, (a) CRF precursor (b) proopiomelanocortin (POMC) (c) P-protachykinin (d) proenkephalin A (e) CGRP precursor (f) preprodynorphin, ie, preproenkephalin B. Terms are...

The curves represent a plot of log (h ) (reduced plate height) against log (v) (reduced velocity) for two very different columns. The lower the curve, the better the column is packed (the lower the minimum reduced plate height). At low velocities, the (B) term (longitudinal diffusion) dominates, and at high velocities the (C) term (resistance to mass transfer in the stationary phase) dominates, as in the Van Deemter equation. The best column efficiency is achieved when the minimum is about 2 particle diameters and thus, log (h ) is about 0.35. The optimum reduced velocity is in the range of 3 to 5 cm/sec., that is log (v) takes values between 0.3 and 0.5. The Knox... 

Now, equations (1) and (2) indicate that both the Knox equation and the Van Deemter equation predict a linear relationship between the value of the (B) term (the longitudinal diffusion term) and solute diffusivity. 

A plot of the (B) term against diffusivity for benzyl acetate and hexamethylbenzene is shown in Figure 4. The predicted linear relationship is clearly confirmed. However,... 

The first term on the right-hand side arises from external eleetrie fields. The seeond (B) term arises from external magnetie induetions interaeting with elee-tronie orbital motion. The SL term arises from eleetron spin-orbital motion interaetions. The Z term arises from the Zeeman interaetion between eleetron spin and the external eleetrie field. Hss arises from eleetron spin-eleetron spin interaetions and includes all hyperfine terms arising from nuclear spins. 

In aqueous solution at room temperature the coefficient B is positive for the majority of electrolytes. For some, however, it is negative in such a case the viscosity at moderate concentrations, where the B term is predominant, is less than that of pure water, while at lower concentrations, where the A s/c term becomes predominant, the value of the viscosity rises above that of pure water. An example of this is shown in Fig. 51, where abcissas are /c. The straight line is a plot of A s/c with A = +0.0052, while the lower curve is a plot of Be with B = —0.033. On adding the ordinates of these two curves the middle curve is obtained, which reproduces, within the experimental error, the values of 17/770 obtained for KC1 in aqueous solution at 18°C. 

TFe data of Popov et alm for Ag contradict the above sequence. They found that pentanol adsorbed more strongly on Ag(100) than on Ag(l 11). Similarly, Cd(0001) adsorbs less strongly than pc-Cd.661 The data for Sb and Bi are to some extent contradictory since the trend is broadly correct but with scatter, which is attributed to the crystal face specificity of space-charge effects.153 For instance, adsorption of cyclohexanol on Bi conforms to the sequence (011) > (101) > (211) > (001) >(111), while the capacitance at a - Ovaries in the sequence (001) > (011) > (211) > (101) > (111). Thus only the faces (001), (211), and (111) are in the expected order. Surprisingly, the Cd data of Lust etal. show similarities with those of Naneva etal.,212 although capacitances disagree. Thus the order of cyclohexanol adsorbability is (1010) > (0001) while the capacitance varies in the order (1010) > (1120) > (0001), i.e., the other way round. In these cases one might wonder whether the G(M-B) term is really independent of face. 

The term is piston and is included only for completeness since it has no effect on the measurement. The b term is the tilt of the off-axis paraboloidal... 

The A term represents the contribution from eddy diffusion, the B term the contribution from longitudinal diffusion, and the C terms the contributions from mass transfer in the mobile and stationary phases to the total column plate height. By differentiating equation (1.31) with respect to the mobile phase velocity and setting the result equal to zero, the optimum values of mobile phase velocity (u ) and plate height (HETP ) can be obtained. 

The a term reflects the strength of the interaction between gas particles, and the b term reflects the particle s size. 

Also, the major change in the logarithm bracket is the change in [A], since the difference between [B]o and [B], will be negligible in comparison, causing a cancellation of the [B] terms on top and bottom. 

Molecular diffusion (the B term) applies to both packed and capillary columns and derives from the fact that all molecules in the gas phase will diffuse into any available space. It is minimized by using an increased flow rate (see the carrier gas velocity in the denominator) and by using a high molecular weight carrier gas. 

The Ea b terms correspond basically to the chemical bonds of the molecule and the EA i B terms to the through-space interactions between non-chemically bonded atoms. 

A is generally positive and predicts (P/>P). B results from the shifts in internal force constants on condensation. An increased force constant on condensation leads in the direction of a normal VPIE, a decrease towards an inverse effect (P different temperature dependences. At low enough temperature A/T2 must predominate. The IE is normal and proportional to 1 /T2. At intermediate temperatures the B term, which can be positive, but more often is negative (see Section 5.4.1), may dominate. This accounts for the commonly observed crossover to inverse IE s. At higher temperatures yet, both terms decay to zero. The temperature dependence of VPIE can thus be complicated. 

The B term represents longitudinal diffusion and is proportional to D ). The C term represents resistance to mass transfer and is proportional to... 

The B-term in the equation is the contribution to the plate height resulting from longitudinal diffusion (molecular diffusion in the axial direction) and arises from the tendency of the solute band to diffuse away from the band center as it moves down a column. It is proportional to the time that the sample spends in the column and also to its diffusion... 

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