Basicity hybridization effects

Pyridine, like benzene, is an aromatic system with six jt electrons (see Section 11.3). The ring is planar, and the lone pair is held in an sp orbital. The increased s character of this orbital, compared with the sp orbital in piperidine, means that the lone pair electrons are held closer to the nitrogen and, consequently, are less available for protonation. This hybridization effect explains the lower basicity of pyridine compared with piperidine. Pyrrole is also aromatic, but there is a significant difference, in that both of the lone pair electrons are contributing to the six-jr-electron system. As part of the delocalized Jt electron system, the lone pairs are consequently not available for bonding to... 

Nicotine has two nitrogen atoms, one as a cyclic tertiary amine and one in a pyridine ring. The basicities are easily distinguished, in that a pyridine system is much less basic than a simple amine. This is essentially a hybridization effect, the nitrogen lone pair in pyridine being held in an sp orbital. This means the lone pair electrons are held closer to the nitrogen, and are consequently less available for protonation than in an sp -hybridized aliphatic amine. Hence, as mentioned above, pyridine has p Ta approximately 5. It follows that pA"a 8.1 is more appropriate for the pyrrolidine nitrogen. 

Aromatic amines are generally less basic than aliphatic amines.This is true both when the nitrogen atom is part of the aromatic system (as in j pyridine, a hybridization effect), and 1 when the nitrogen atom is bonded to the aromatic ring (as in aniline,... 

Hybridization effects Increasing the percent s-character in Pyridine is iess basic than piperidine, the orbitai with the lone pair decreases basicity. 

It is well-known that a-overlap of two p-orbitals or two s-orbitals does not take full advantage of the available orbital density. In order to maximize o-overlap, the interacting atoms change their orbital shapes in a non-symmetric way (rehybridize). Because hybridization is associated with changes in orbital overlap, it can be considered as one of the most basic stereoelectronic effects that can impose significant modulations on other stereoelectronic interactions. 

Furthermore, these hybridization effects correlate well with the donor ability and basicity of substituted anilines as illustrated in Figure 5.212 Remarkably, relatively small changes in s-character are associated with basicity changes in the order of several pK units. 

Applying p/C Values in Organic Acid-Base Reactions 3. EFFECT QF STRUCTURE QN ACIDITY Effect of Periodic Trends on Acidity and Basicity Effect of Resonance on Acidity and Basicity Inductive Effects Effect of Hybridization on Acidity... 

In this work hybrid method is suggested to determine anionic surfactants in waters. It is based on preconcentration of anionic surfactants as their ion associates with cationic dyes on the membrane filter and measurement of colour intensity by solid-phase spectrophotometry method. Effect of different basic dyes, nature and hydrophobicity of anionic surfactants, size of membrane filter pores, filtration rate on sensitivity of their determination was studied. Various cationic dyes, such as Methylene Blue, Crystal Violet, Malachite Green, Rhodamine 6G, Safranin T, Acridine Yellow were used as counter ions. The difference in reflection between the blank and the sample was significant when Crystal Violet or Rhodamine 6G or Acridine Yellow were used. 

Resonance effects are also important in aromatic amines. m-Nitroaniline is a weaker base than aniline, a fact that can be accounted for by the —7 effect of the nitro group. But p-nitroaniline is weaker still, though the —I effect should be less because of the greater distance. We can explain this result by taking into account the canonical form A. Because A contributes to the resonance hybrid, " the electron density of the unshared pair is lower in p-nitroaniline than in m-nitroaniline, where a canonical form such as Ais impossible. The basicity is lower in the para compound for two reasons, both... 

Multiparticle collision dynamics describes the interactions in a many-body system in terms of effective collisions that occur at discrete time intervals. Although the dynamics is a simplified representation of real dynamics, it conserves mass, momentum, and energy and preserves phase space volumes. Consequently, it retains many of the basic characteristics of classical Newtonian dynamics. The statistical mechanical basis of multiparticle collision dynamics is well established. Starting with the specification of the dynamics and the collision model, one may verify its dynamical properties, derive macroscopic laws, and, perhaps most importantly, obtain expressions for the transport coefficients. These features distinguish MPC dynamics from a number of other mesoscopic schemes. In order to describe solute motion in solution, MPC dynamics may be combined with molecular dynamics to construct hybrid schemes that can be used to explore a variety of phenomena. The fact that hydrodynamic interactions are properly accounted for in hybrid MPC-MD dynamics makes it a useful tool for the investigation of polymer and colloid dynamics. Since it is a particle-based scheme it incorporates fluctuations so that the reactive and nonreactive dynamics in small systems where such effects are important can be studied. 

Generally, there are a number of ways in which the adsorption and binding of charged macromolecules (in particular, DNA immobilization and hybridization) can affect the electrochemical properties of the analyte-FED interface. In the case of field-effect devices, two basic effects are usually considered ... 

The alternative possibility of protonation of amidines on the amino-nitrogen depends on its basicity, after its lone pair of electrons has been localized. This localization energy is not known and neither is the inductive effect of the residue attached to the amino-nitrogen in [36], but an amino-nitrogen attached to an -hybridized carbon... 

Fig. 4 Effect of spacer length on the mean hybridization intensity at five probe lengths. The basic single spacer unit had a length equivalent to a dT OND, so the scale is based on the equivalent number of nucleotides. Intensities were normalized to the intensity obtained using the 25mer probe with no added spacer [20]...

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