Trigonal planar shape

Figure 1.35 The triangular (trigonal planar) shape of boron trifluoride maximally separates the three bonding pairs.

This molecule is of the AX3 type it has a trigonal planar electron-group geometry and a trigonal planar shape. 

The NF3 molecule has two extra electrons, compared to BF3, which would occupy an anti-bonding 7t-type 2a/ orbital if it had a trigonally planar shape. The C1F3 molecule with another two electrons would make use of the anti-bonding or-type 4a,7 orbital if the molecule were to be trigonally planar. It is to avoid use of anti-bonding orbitals that they adopt different symmetries. 

Find a flowering plant that interests you. Look at the root formation, leaf shapes and how they are attached to the stem, and the shape of the flower. Draw these different shapes. Find molecules that resemble these different shapes. Remember that group 3A elements form trigonal planar shaped molecules, group 4A elements form tetrahedral shaped molecules, group 5A elements form pyramid shaped molecules and group 6A elements form bent shaped molecules. Carbon chains have a zigzag shape and the DNA molecule is a double helix. You will see that these molecular shapes are duplicated in natural objects. See how many molecular shapes you can find in an ordinary flower. 

The hybridised orbitals and the 2py orbital occupy spaces as far apart from each other as possible. The lobes of the 2p orbital occupy the space above and below the plane of the x and z axes. The three hybridised sp2 orbitals (major lobes shown only) will then occupy the remaining space such that they are as far apart from the 2py orbital and from each other as possible. Thus, they are all placed in the x-z plane pointing towards the corner of a triangle (trigonal planar shape). The angle between each of these lobes is 120. We are now ready to look at the bonding of an sp2 hybridised carbon. 

In alkenes all the four bonds formed by carbon are not c-bonds. In this case of sp2 Hybridisation the three half-filled sp2 hybridised orbitals form a trigonal planar shape. The use of these three orbitals in bonding explains the shape of an alkene,... 

The carbon atom in a typical carbocation is sp hybridized. The pz orbital is empty and is perpendicular to the plane of the other three bonds. Thus, carbocation adopts a trigonal planar shape. 

If these three orbitals are degenerate, what configuration relative to each other will they adopt These three orbitals will form a trigonal planar shape, with a bond angle of 120°. This leaves the last p orbital to project above and below the plane formed by the... 

The value of the dot and cross structure here is to help to ensure that all the electrons are accounted for before attempting to deduce the structure. The electron pair repulsion theory gives the result that the CC12 molecule has a trigonal planar shape. There are two C-Cl single bonds and also (formally)... 

Earlier, we looked at the BC13 molecule and observed that it adopted a trigonal planar shape. 

The aluminium trichloride monomer adopts a trigonal planar shape, with an empty orbital that extends above and below the plane in which the Al-Cl bonds are located. However, aluminium trichloride forms a dimer at room temperature and pressure. Suggest a structure for this dimer. 

The hybridisation between one s orbital and two p orbitals results in three sp hybrid orbitals, which form a trigonal planar shape. In this scenario, the third p orbital is left unhybridised, and is at... 

The C=C bond is treated as though it were a single bond. Because there are no lone pairs present, the arrangement around each C atom has a trigonal planar shape like BF3, discussed earlier. Thus the predicted bond angles in C2H4 are aU 120°. 

An sp hybridized nitrogen centre is consistent with the trigonal planar shape of [N03]. Allow the hybrid orbitals to overlap with suitable orbitals from oxygen a choice of sp hybridization on the O atom provides suitable orbitals to accommodate the oxygen lone pairs. Occupation of each bonding orbital by a pair of electrons gives three equivalent N—O f7-bonds ... 

The nitrate ion (NO3 ) is one of several polyatomic ions with the trigonal planar shape. One of three resonance forms of the nitrate ion (Sample Problem 10.4) is... 

Step 4. Draw and name the molecular shape With three electron groups and no lone pairs, COCI2 has a trigonal planar shape (AX3) ... 

Substitution of carboxylic acids occurs through a two-step sequence addition plus elimination equals substitution. Addition to the trigonal planar shape of the carbonyl group gives an unstable tetrahedral species, which immediately undergoes elimination to revert to a trigonal planar product ... 

Figure 8.18 Electron pairs in a molecule are located as far apart as they can be, just as these balloons are arranged. Two pairs form a linear shape. Three pairs form a trigonal planar shape. Four pairs form a tetrahedral shape. 

The three bonding electron pairs in AICI3 have maximum separation in a trigonal planar shape with 120° bond angles. 

The three electron pairs around boron minimize the repulsion between them when the molecule adopts the trigonal planar shape. The fluorine atoms are in the same plane, at the three corners of a triangle drawn around the central atom. The three angles between the B-F bonds are all 120°. 

The isomers described to this point have had octahedral or square-planar geometry. In this section, we describe other geometries. Explanations for some of the shapes are consistent with VSEPR predictions (Chapter 3), with the general assumption that the metal d electrons are stereochemically inactive. In these cases, 3-coordinate complexes have a trigonal-planar shape, 4-coordinate complexes are tetrahedral, and so forth, assuming that... 

An important problem that needs to be faced when using radical reactions to stereoselectively form asymmetric centers is that most carbon-centered radicals are planar or nearly so. Once a carbon radical has been created it usually adopts a trigonal planar shape, or nearly so, and both faces of the radical are identical. For example, following abstraction of a halogen atom (by the BujSn radical) from the... 

Five electron pairs Start with the trigonal planar shape that exists with three electron pairs, and then envision sticking a skewer straight through the sheet of paper. 

Balloon models used to predict bond angles. (a)Two balloons assume a linear shape with a bond angle of 180° about the tie point. (b)Three balloons assume a trigonal planar shape with bond angles of 120° about the tie point, (c) Four balloons assume a tetrahedral shape with bond angles of 109.5° about the tie point. 

Thus, IBr has a nonzero dipole moment, which points from the Br atom to the I atom, (b) Because fluorine is more electronegative than boron, each B—F bond in BF3 (boron trifluoride) is polar, and the three bond moments are equal. According to the VSEPR model, however, BF3 should be trigonal planar and the symmetry of the trigonal planar shape means that the three bond moments exactly cancel one another ... 

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