Carbon molecular shape

In the main, the physical and chemical properties of saturated and partially unsaturated alicyclic compounds closely resemble those of the analogous acyclic compounds formally derived by cleavage of the carbon ring at a point remote from any functionality. Relatively small, but often significant, differences in properties arise from conformational effects, and from strain effects in small rings, and these differences can be striking in properties which are particularly sensitive to molecular shape. 

Of the various geometric parameters associated with molecular shape, the one most nearly constant from molecule to molecule and most nearly independent of substituent effects is bond length. Bond lengths to carbon depend strongly on the hybridization of the carbon involved but are little influenced by other factors. Table 1.2 lists the interatomic distances for some of the most common bonds in organic molecules. The near constancy of bond lengths from molecule to molecule reflects the fact that the properties of individual bonds are, to a good approximation, independent of the remainder of the molecule. 

Can you imagine atoms connected together to form a molecule shaped like a minuscule soccer ball How about connections that result in molecular tubes Remarkably, the element carbon can form these molecular shapes. Perhaps even more remarkably, chemists did not discover this until late in the twentieth century. 

Many elements of the periodic table, from titanium and tin to carbon and chlorine, exhibit tetrahedral electron group geometry and tetrahedral molecular shapes. In particular, silicon displays tetrahedral shapes in virtually all of its stable compounds. 

The carbon atom in CO2 has two groups of electrons. Recall from our definition of a group that a double bond counts as one group of four electrons. Although each double bond includes four electrons, all four are concentrated between the nuclei. Remember also that the VSEPR model applies to electron groups, not specifically to electron pairs (despite the name of the model). It is the number of ligands and lone pairs, not the number of shared eiectrons, that determines the steric number and hence the molecular shape of an inner atom. 

Determine the Lewis structure and the molecular shapes of the carbon atoms of this molecule. Suggest a reason for the reactivity of C3 Hg. ... 

Direct H—C dipole-dipole coupling dominating 13C relaxation (for protonated carbons) information about molecular shapes and motion are contained in the experimental spin-lattice relaxation times. 

The previous approach is valid as long as the molecular reorientation can be described by a single correlation time. This excludes molecules involving internal motions and/or molecular shapes which cannot, to a first approximation, be assimilated to a sphere. Due to its shape, the molecule shown in Figure 15 cannot evidently fulfil the latter approximation and is illustrative of the potentiality of HOESY experiments as far as carbon-proton distances and the anisotropy of molecular reorientation are concerned.45 58... 

However, the important new feature of metal alkylidenes (4.51) is metal-carbon pi-bonding. As discussed in Section 2.8, pi bonds between transition metals and main-group elements are of d -p type, much stronger than corresponding p —pn bonds between heavier main-group elements. Compared with simple metal hydrides and alkyls, metal-carbon pi-bonding in metal alkylidenes affects the selection of metal d orbitals available for hybridization and skeletal bond formation, somewhat altering molecular shapes. 

In this section, you studied carbon bonding and the three-dimensional shapes of organic molecules. You learned that you can determine the polarity of a molecule by considering its shape and the polarity of its bonds. In Unit 2, you will learn more about molecular shapes and molecular polarity. In the next section, you will review the most basic type of organic compound hydrocarbons. 

Compare two molecules with the same molecular shape CCI4 and CCI3H. Since the polarity of the C—Cl bond is different from that of the C—H bond, the polarities of these two molecules are different. The CCI4 molecule is symmetrical about any axis joining the two atoms of the C—Cl bond. The polarities of the C—Cl bonds counteract one another. Thus, the carbon tetrachloride molecule is non-polar. In the case of CCI3H, the polarity of the H — Cl bond is different from that of the three C—Cl bonds. Thus, the molecule is polar. 

The AO s of carbon can hybridize in ways other than sp as shown in Fig. 2-7. Repulsion between pairs of electrons causes these HO s to have the maximum bond angles and geometries summarized in Table 2-2. The sp and sp HO s induce geometries about the C s as shown in Fig. 2-8. Only a bonds, not v bonds, determine molecular shapes. 

It is important to realize that methane is not tetrahedral because carbon has sp3, hybrid orbitals. Hybridization is only a model—a theoretical way of describing the bonds that are needed for a given molecular structure. Hybridization is an interpretation of molecular shape shape is not a consequence of hybridization. 

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. 

When we studied organic molecules in Chapter 5, we realized that chains of carbon atoms with branches appear in a variety of shapes. Cyclic molecules were possible. Catalysts worked to change the rate of a chemical reaction because one molecule fit into another, like puzzle pieces. Catalysts worked because of the molecular shapes of the interacting molecules. Clearly, molecules have distinct shapes. 

Structure of fullerene-Cy,o (a) molecular shape, (b) valence-bond formula, and (c) planar formula with carbon atom-numbering scheme. 

The influence of atoms other than carbons in a sp3 hybrid state on the molecular shape is accounted for by the Kappa alpha shape indices. They can be obtained by modifying each a and mp, in Equation 5.19 to Equation 5.22, with a value ... 

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