Inductive contributions

While it is difficult to rule out an inductive contribution to the secondary a-deuterium KIEs in these Menshutkin SN2 reactions, the steric origin of these KIEs is clearly indicated by the inverse secondary a-deuterium KIEs found in an extensive study of the SN2 Menshutkin reactions between substituted... 

Table 30 Structural features for the substrates in the gas-phsae heterolysis of several (CH3)2CH—X at 25°C, the calculated /3-deuterium-d6 EIEs and the hyperconjugative and inductive contributions to the EIE."... 

X Planarity at Ca C Cp bond length (A) 0,-H bond length (A) Calculated (kHlkD)l p-d6 EIE Hyperconjugative contribution to the EIE Inductive contribution to the EIE Percentage inductive EIE... 

Hie present authors (O.M. and K.W.) believe that the inductive KIE would be very much less than 0.71 because only the deuteriums close to the reaction centre would have a significant inductive contribution to the KIE. In fact, a secondary inductive KIE might be as small as a few per cent, i.e., kHlkD 0.96. 

The two-parameter equation suggested by Jencks and co-workers (Eq. 22) separates substituent effects into a polar or inductive contribution described by p and a resonance contribution described by p. ... 

The N2-N2 spectra, Fig. 3.20, consist of the unresolved N2 rotational band at frequencies from 10 to 220 cm-1. Both quadrupole and hexade-capole induction contribute significantly to the observed spectra. Induced... 

Figure 4.1 shows the four significant induced dipole components for the rototranslational bands (left panel). The isotropic and anisotropic overlap components, B01 and — B21, dominate at near range (dotted). These fall off roughly exponentially with separation R so that at more distant range, the quadrupole-induction, B23, dominates it falls off more slowly, like R 4. A weak hexadecapole component, B45, is also present. The dashed lines show the classical (i.e., overlap-free) multipole induction contributions. These differ only at near range from the computed B23 and B45 components,... 

Evidence against an inductive contribution comes from experimental IEs on amine basicity. According to Equation (28), there is no angle-independent term. This is the term that would arise from an electrostatic interaction between a positive charge on the N and a C-H or C-D bond dipole.3 Although Equation (28) is imperfect, and there are smaller IEs from synperiplanar C-D, we conclude that an inductive effect is too small to contribute to the observed IE. 

Moreover, the inductive contribution of a p deuterium to the IE on amine basicity was estimated.31 The inductive effect on pK due to an sp2-sp3 C-C bond, with a dipole moment of 0.35 D, as in propene, can be assigned as 0.95, the ApAf between allylamine and methylamine. Above, in connection with the structural question of the extent to which IEs affect dipole moments, dCu dco is 0.5 pm and dfi/dd is 0.004e. These combine to a ApAT on deuteration of 0.001, which is much smaller than the measured IEs in Table 5. An inductive contribution does exist, but it is negligible. 

Another estimate seemed to support an inductive contribution to deuterium IEs on the acidity of carboxylic acids.37 This IE on acidity of some carboxylic acids was attributed to an inductive effect arising from the electrostatic interaction of the C-H or C-D dipole with the negative charge of the carboxylate, as expressed in Equation (31). The derivative dpK/dfi was estimated from the effect of a C-Cl dipole on acidity, using the difference in pATas of trichloroacetic acid (0.63) and acetic acid (4.75) and the difference between the dipole moments of t-butyl chloride (2.13 D) and isobutane (-0.13 D). Next Afj, was estimated as 0.0086 D, the difference between the dipole moments of (CH3)3CD and (CH3)3CH. Thus ApK was estimated as 0.005 per D, in excellent agreement with the observed 0.014 for acetic-d3 acid. Moreover, the IE of 0.002 per D in pivalic-J9 acid is consistent with a 2.8-fold falloff factor for inductive effects. Yet those estimates depend crucially on the difference between the dipole moments of isobutane and isobutane-d, which is unusually large, amounting to 6.5% of either s total dipole moment. 

Enhancement of P by an inductive contribution can also be seen in fluorinated ketones. For example, 4-methoxyben-zaldehye has a P of 2.2 x 10 30 esu and 1 of 3.5 Debye while the trifluoromethyl ketone compound (21) as the ac-... 

When a polar molecule and a non-polar molecule approach each other, the electric field of the polar molecule distorts the electron charge distribution of the non-polar molecule and produces an induced dipole moment within it. The interaction of the permanent and induced dipoles then results in an attractive force. This induction contribution to the electrostatic energy is always present when two polar molecules interact with each other. 

The first derivative of the density matrix with respect to the magnetic induction (dPfiv/dBi) is obtained by solving the coupled-perturbed Hartree-Fock (or Kohn-Sham) equations to which the first derivative of the effective Fock (or Kohn-Sham) operator with respect to the magnetic induction contributes. Due to the use of GIAOs, specific corrections arising from the effective operator Hcnv describing the environment effects will appear. We refer to Ref. [28] for the PCM model and to Ref. [29] for the DPM within either a HF or DFT description of the solute molecule. 

The results of two-parameter correlations of the 13C and 15 N NMR chemical shifts of 2-substituted 5(6)-nitrobenzimidazoles with the induction and resonance constants (a, ak) are given in Table 3.26 [688, 689], The electronic influence of substituents on the chemical shifts of carbons (and protons) in positions 4 and 7 are mainly transmitted by a resonance mechanism, C-4 being more sensitive than C-7 to the substituent effect. For positions 5 and 6 a slightly smaller contribution from the resonance component to the total transmission of substituent effects is observed. However, analysis of correlation between 5 15 N and substituent parameters indicates an approximately equal influence of the induction and resonance substituent effects on the nitro group shielding (see Table 3.26) [688, 689], When other sets of substituent constants (F and R, c, and ck, etc.) are used in the correlation the percentage ratios of resonance and inductive contributions remain unchanged. 

Improved understanding and treatment of the phenyl case was developed from the recognition that the derived o-si (C6H5-) is almost identical with the "standard Hammett o- value, a parameter containing both mesomeric and inductive contributions. Since published data on the krei of ozonation of substituted phenyldimethylsilanes were available (11), and included the common point, phenyldimethylsilane, simple mathematical manipulation could bring these and the present data on to the same scale. When the Hammett o- for the substituted phenyls was... 

The exo/endo rate ratio in the unsaturated series compares closely to that observed with the saturated tosylates homoconjugative interaction is therefore not apparent. Also, the products were those expected for solvolysis without participation.373 The dihydrotriquinacenyl tosylates solvolyze more slowly due die inductive contributions of the double bonds. The geometry of the p7T orbitals in the exo isomer are seen to have a very poor alignment for neighboring group participation. 

Phenomenological evaluation [85,86] using atomic and molecular polarizabilities and the permanent dipole moment of water suggests that under the condition of the experiment, which involve water at high rotational temperature, the long range attraction is accounted for more than 90% by dispersion forces, while induction contributions play a minor role. 

It is possible to apply the mxiltipole e q>ansion and perturbation theory in order to derive long range expressions for Tj (R), thus relating this quantity to monomer I operties. A simple example of sudi a procedure can be found in the appendix of ref. where the induction contribution to the dipole moment (J = 1) of an arbitrary Van der Waals dimer has been evaluated. 

The measurement of interaction dipoles by beam deflection gives an indk ation of the structure of the Van der Waals molecule. A recent example is given by Howard and coworkers , who experimentally established that the interaction dipole of ( 2)2 is less than 10 D. Since it has sometimes been suggested that the dimer is a T-shaped complex (a favourable configuration for quadrupole-quadrupole interaction, see above), they estimated the induction contribution to the dipole moment for this conformation (at R = 4.1 A) and found 0.18 D for this value. So they conclude that the dimer has most likely a staggered parallel configuration, which is in accordance with recent ab initio calculations . ... 

The first ab initio calculations on interaction dipoles were performed by Matcha and Nesbet They considered the systems HeNe, HeAr and NeAr as super-molecules and did ordinary Hartree-Fock-LCAO-SCF calculations in the range R = 2.0 to 5.5aQ. Because of the Hartree-Fock approximation they did not obtain the dispersion contribution to the dipole moment (cf. sect. 2), but only exchange, penetration and overlap-induction contributions. Their ab initio dipoles could be fitted quite well by a single exponential, which supported the assumption made earlier by Van Kranendonk ... 

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