Hybridization effects

At 146 pm the C 2—C 3 distance m 1 3 butadiene is relatively short for a carbon-carbon single bond This is most reasonably seen as a hybridization effect In ethane both carbons are sp hybridized and are separated by a distance of 153 pm The carbon-carbon single bond m propene unites sp and sp hybridized carbons and is shorter than that of ethane Both C 2 and C 3 are sp hybridized m 1 3 butadiene and a decrease m bond distance between them reflects the tendency of carbon to attract electrons more strongly as its s character increases... 

Electronegativity and hybridization effects combine to make the carbon of a carbonyl group especially deshielded Normally the carbon of C=0 is the least shielded one m... 

The carbon-halogen bonds of aryl halides are both shorter and stronger than the carbon-halogen bonds of alkyl halides In this respect as well as m their chemical behavior they resemble vinyl halides more than alkyl halides A hybridization effect seems to be responsible because as the data m Table 23 1 indicate similar patterns are seen for both carbon-hydrogen bonds and carbon-halogen bonds An increase m s... 

The hydrogen-deuterium exchange rates for 1,2-dimethylpyrazolium cation (protons 3 and 5 exchange faster than proton 4 Section 4.04.2.1.7(iii)) have been examined theoretically within the framework of the CNDO/2 approximation (73T3469). The final conclusion is that the relative reactivities of isomeric positions in the pyrazolium series are determined essentially by inductive and hybridization effects. 

Hybridization Effects. Here again, the effects are similar- to those seen in H NMR. As illustrated by 4- hybridized ones. 

The increase of the total magnetic moment from USe to UTe is the result of the decrease of spin moment from 5f electrons due to the stronger hybridization effects between U atom and Te atom. 

Using, e.g., the NAO Fock-matrix elements for Li2+ quoted in note 11 (together with the corresponding value for /ss/ = (lsA F lsB) = —0.0668), we obtain the estimate Fab — —0.0910. This somewhat underestimates the magnitude of the actual interaction element (—0.1191), but shows the general direction and strength of the hybridization effect. 

Control of steric repulsion with positively charged ortho substituents 20 Hybridization effects 21... 

Calculated sp-Electron and spd-Hybridization Effects on the Magnetic Properties of Small FeN Clusters. 

Outer C—N bonds. Outer C—N bonds in the R—N—C—N—R moiety are known22,26 to inversely depend on the adjacent inner bond lengths probably due to a hybridization effect. Natural bond lengths for those bonds were determined according to ... 

Results obtained from the alkali iodides on the isomer shift, the NMR chemical shift and its pressure dependence, and dynamic quadrupole coupling are compared. These results are discussed in terms of shielding by the 5p electrons and of Lbwdins technique of symmetrical orthogonalization which takes into account the distortion of the free ion functions by overlap. The recoilless fractions for all the alkali iodides are approximately constant at 80°K. Recent results include hybridization effects inferred from the isomer shifts of the iodates and the periodates, magnetic and electric quadrupole hyperfine splittings, and results obtained from molecular iodine and other iodine compounds. The properties of the 57.6-k.e.v. transition of 1 and the 27.7-k.e.v. transition of 1 are compared. 

The alkane propane has pATa 50, yet the presence of the double bond in propene means the methyl protons in this alkene have pATa 43 this value is similar to that of ethylene (pATa 44), where increased acidity was rationalized through sp hybridization effects. 1,3-Pentadiene is yet more acidic, having pATa 33 for the methyl protons. In each case, increased acidity in the unsaturated compounds may be ascribed to delocalization of charge in the conjugate base. Note that we use the term allyl for the propenyl group. 

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. 

Another important feature of the ZnS Mn/AA nanocrystal is that PAA is excited by the photon, which simultaneously can excite ZnS with the same energy. This eases energy transfer from PAA to ZnS Mn. At the same time, coordination of AA or PAA to ZnS Mn increases the local electron density around the COO group due to the abstraction of some S2- ions at the moment of oxidation to S6+ as we observed from IR and XPS spectra. The electrons concentrated near COO- might contribute to enhance the quantum efficiency of the energy transfer from the s-p exciton of ZnS to the d band of Mn(II). All these hybrid effects involved in the ZnS.Mn/AA enhance the PL intensity as a whole. 

Fig. 8. d -p hybridization effects in angular ML2 fragments that encourage more effective metal-olefin back donation. 

The ElcB mechanism has the same features as the E2 mechanism except that proton abstraction by the base proceeds essentially to completion prior to departure of the leaving group. A variant of this mechanism may intervene whenever the leaving group is a poor leaving group or an exceptionally stable carbanion may be formed (i.e., due to the presence of Z substituents in addition to the polar a bond and/or a hybridization effect). The factors which lead to stabilization of carbanions have been discussed in Chapter 7. 

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