Sp2, sp3 hybridization

Molander, G. A. Kollner, C. Development of a protocol for eight- and nine-membered ring 488 synthesis in the annulation of sp2,sp3-hybrid-ized organic dihalides with keto esters. /. Org. Chem. 2000, 65, 8333-8339. 

Gao M, Thorpe SB, Santos WL. sp2-sp3 Hybridized mixed diboron synthesis, characterization, and copper-catalyzed p-boration of a,p-unsaturated conjugated compounds. Org Lett. 2009 11 3478-3481. 

When we discussed sp3 hybrid orbitals in Section 1.6, we said that the four valence-shell atomic orbitals of carbon combine to form four equivalent sp3 hybrids. Imagine instead that the 2s orbital combines with only two of the three available 2p orbitals. Three sp2 hybrid orbitals result, and one 2p orbital remains unchanged- The three sp2 orbitals lie in a plane at angles of 120° to one another, with the remaining p orbital perpendicular to the sp2 plane, as shown in Figure 1.13. 

In addition to compounds with planar, sp2-hybridized carbons, compounds with tetrahedral, sp3-hybridized atoms can also be prochiral. An vp3-hybridizec) atom is said to be a prochirality center if, by changing one of its attached groups, it becomes a chirality center. The —GH2OH carbon atom of ethanol, for instance, is a prochirality center because changing one of its attached -H atoms converts it into a chirality center. 

A molecule is prochiral if can be converted from achiral to chiral in a single chemical step. A prochiral sp2-hybridized atom has two faces, described as either Re or Si. An sp3-hybridized atom is a prochirality center if, by changing one of its attached atoms, a chirality center results. The atom whose replacement leads to an R chirality center is pro-R, and the atom whose replacement leads to an S chirality center is pro-S. 

Another trend is that sp3-hybridized carbons generally absorb from 0 to 90 8, while sp2 carbons absorb from 110 to 220 8. Carbonyl carbons (C=0) are... 

Humulene. structure of, 202 Hund s rule, 6 sp Hybrid orbitals. 17-18 sp2 Hybrid orbitals, 15. sp3 Hybrid orbitals, 12-14 Hydrate, 701... 

In diamond, carbon is sp hybridized and forms a tetrahedral, three-dimensional network structure, which is extremely rigid. Graphite carbon is sp2 hybridized and planar. Its application as a lubricant results from the fact that the two-dimensional sheets can slide across one another, thereby reducing friction. In graphite, the unhybridized p-electrons are free to move from one carbon atom to another, which results in its high electrical conductivity. In diamond, all electrons are localized in sp3 hybridized C—C cr-bonds, so diamond is a poor conductor of electricity. 

The chemical shifts of jp3-hybridized silicon atoms, such as a trimethyl-silyl group attached to the jp2-hybridized silicon in silenes, are normally found from -10 to -18 ppm, as compared to the position at -9.8 ppm for the trimethylsilyl groups of (Me3Si)4Si (the central silicon atom of this compound resonates at -135.5 ppm). On the other hand, a trimethylsiloxy group attached to carbon, either sp2- or sp3-hybridized, normally absorbs in the range from +5 to +20 ppm. 

Figure 3.17 Geometry of hybrid orbitals, (a) digonal sp hybrids oppositely directed along the same axis (b) trigonal sp2 hybrids pointing along three axes in a plane inclined at 120° (c) tetrahedral sp3 hybrids pointing towards the comers of a regular tetrahedron. (Reproduced with permission from R. McWeeny, Coulson s Valence, 1979, Oxford University Press, Oxford.)...

To create a chiral center at an sp3-hybridized carbon requires a chiral environment to stereodirect the reaction. This chiral environment may exist as a chirally substituted sp3-hybridized carbon, on which appropriate substitution creates a new molecule with the same or inverted chirality at the former chiral center or as a chiral arrangement near a prochiral (prechiral) sp2 carbon. 

In the case of an sp2-hybridized carbon containing three different substituents (prochiral), the addition of a fourth kind of substituent to form an sp3-hybridized carbon creates a new chiral center (Fig. 3.1). 

Additional bonds are thus donor bonds, and to accept electron pairs from neutral and anionic ligands, zinc uses the two remaining 4p orbitals to form sp2 and sp3 hybrids. In the absence of steric effects, discrete, homoleptic, anionic tri- and tetraorganozinc compounds (zincates) have almost always ideal trigonal-planar and tetrahedral geometries, respectively. 

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