Hybridization trigonal

In this case, there are three equivalent hybrid orbitals, each called sp (trigonal hybridization). This method of designating hybrid orbitals is perhaps unfortunate since nonhybrid orbitals are designated by single letters, but it must be kept in mind that each of the three orbitals is called sp. These orbitals are shown in Figure 1.4. The three axes are all in one plane and point to the comers of an equilateral triangle. This accords with the known structure of boron trifluoride (BF3), a planar molecule with angles of 120°. 

Protonation of the alkyne is actually less favourable than protonation of an alkene, because the resulting vinyl cation is sp hybridized, having a bonds to just two substituents, a it bond, and a vacant p orbital. A vinyl cation is thus less stable than a comparable trigonal -hybridized carbocation, since ip-hybridization brings bonding electrons closer to carbon it thus becomes less tolerant of positive charge. Protonation, when it occurs, will be on... 

A full valence orbital VB calculation in this basis involves 784 standard tableaux functions, of which only 364 are involved in 68 2" symmetry functions. For CH3 we present the results in terms of sp hybrids. This has no effect on the energy, of course. We show the principal standard tableaux functions in Table 13.5. The molecule is oriented with the C3 -axis along the z-axis and one of the H atoms on the x-axis. The three trigonal hybrids are oriented towards the H atoms. The x subscript on the orbital S5unbols in Table 13.5 indicates the functions on the x-axis, the a subscript those 120° from the first set, and the 6 subscript those 240° from the first set. 

It is possible to form a third type of s-p hybrid containing one s orbital and two p orbitals. This is called an sp2 or trigonal (ir) hybrid. It consists of three identical orbitals, each of which does not differ appreciably in shape from Fig. 5.3 and is directed toward the corner of an equilateral triangle. The angles between the axes of the orbitals in a trigonal hybrid are thus all 120°. 

Phosgene (C,J. A Lewis structure for OCCl has eight electrons about the carbon, but one pair forms the -jt bond of the double bond, so again an sp or trigonal, hybridization will be the most stable (Fig. 6.1c). 

In this case we can transform these into three equivalent orbitals which are s-p hybrids (called trigonal hybrids) pointing towards the vertices of an equilateral triangle, so that the angle between neighbouring directions is 120°. The actual transformation is... 

Left the unhybridized 2p atomic orbitals of the carbon atoms are shown superimposed on the trigonally-hybridized sp2 sigma bonding system. Right overlap ofthe sp2 orbitals leads to a pi orbital system that extends around the molecule... 

The hybridization on the nitrogen atom is sapcrb with a = 1.20 and b = 2.36 - 2.51, which is dramatically different from the s pa-2 trigonal hybrid. The discrepancy is more marked in the case of compounds 1, 40, 41, and 43 with one bridgehead nitrogen atom. On the other hand, the hybridization on carbon atoms is close to the s pa2 trigonal hybrid. 

Fifl. 8. (a) The spherically symmetrical Is orbital for H (b) tetrahedral hybrid orbitals for B (c) trigonal hybrid orbitals for B, showing the 7r-orbital extending above and below the plane of the sp hybrids... 

Boron Trichloride, BCI3. Here the molecule is planar, with the boron atom at the centre of an equilateral triangle of chlorine atoms (Fig. 46). The valence state must be described in terms of three similar hybrid AO s pointing towards the comers of the triangle. Such orbitals can be formed by mixing 2s and two 2p AO s, 2p and 2p say they lie in the plane of the latter and are precisely equivalent (Fig. 47). If the so-called trigonal hybrids are denoted by h, hg and hg, the appropriate boron valence state must be B(ls2 h h2 hg ). The hybrid AO s overlap chlorine 3p AO s, directed towards the boron atom, to form localised MO s similar to those in beryllium chloride. 

Trigonally hybridized vinyllithium derivatives are characterized by higher configurational stability [34,35]. Panek [36] demonstrated that (E) and (Z)-l-lithium-l-phenyl-l-butene could be prepared stereospecifically, with retention of configuration, by a lithium-halogen exchange reaction between n-butyllithium and (Z) and ( )-l-bromo-l-phenyl-1-butene, respectively (Scheme 7). Both lithium derivatives are configurationally stable at... 

Consider the electronic configuration of the cyclopentadienyl anion (Fig. 10.5). Each carbon, trigonally hybridized, is held by a a bond to two other carbons... 

Now, what evidence is there that other Hiickel numbers—1, 10, 14, etc.— are also magic numbers We cannot expect aromatic character necessarily to appear here in the form of highly stable compounds comparable to benzene and its derivatives. The rings will be too small or too large to accommodate trigonally hybridized atoms very well, so that any stabilization due to aromaticity may be largely offset by angle strain or poor overlap of p orbitals, or both. 

Triclinic crystal system, 75, 78 Trigonal bipyramidal (TBP) structure, 480-483 Trigonal crystal system, 75, 78 Trigonal hybrid, 150-153 Trigonal prism, 489-491 Trimethylborane, 205 Trinegative ions, 332-333 Trinuclear clusters, 813-815 Tropylium complexes, 683-684 Tutankhamen, 458 Twist angles, 490... 

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