Bond angles benzene

Benzene is planar and its carbon skeleton has the shape of a regular hexagon There IS no evidence that it has alternating single and double bonds As shown m Figure 111 all the carbon-carbon bonds are the same length (140 pm) and the 120° bond angles... 

FIGURE 11 1 Bond distances and bond angles of benzene... 

The structural facts that benzene is planar all of the bond angles are 120° and each car bon IS bonded to three other atoms suggest sp hybridization for carbon and the frame work of CT bonds shown m Figure 11 3a... 

Further evidence for the unusual nature of benzene is that all its carbon-carbon bonds have the same length—139 pm—intermediate between typical single (154 pm) and double (134 pm) bonds. In addition, an electrostatic potential map shows that the electron density in all six carbon-carbon bonds is identical. Thus, benzene is a planar molecule with the shape of a regular hexagon. All C-C—C bond angles are 120°, all six carbon atoms are sp2-hybridized. and each carbon has a p orbital perpendicular to the plane of the six-membered ring. 

Pyridine is a flat, hexagonal molecule with bond angles of 120°. It undergoes substitution rather than addition and generally behaves like benzene. Draw a picture of the 7T orbitals of pyridine to explain its properties. Check your answer by looking ahead to Section 15.7. 

E Benzene is planar and has the shape of a regular hexagon. All bond angles are 120°, all carbon atoms are sp2-hybndized, and all carbon-carbon bond lengths are 139 pm. 

In these line-angle formulas it is understood that there is a carbon atom at each vertex of the hexagon hydrogen atoms are not shown. This model is consistent with many of the properties of benzene. The molecule is a planar hexagon with bond angles of 120°. The hybridization of each carbon is sp2. However, this structure is misleading in one respect Chemically, benzene does not behave as if double bonds were present... 

Bent molecule Molecule containing three atoms in which the bond angle is less than 180° examples include H20 and S02,178 Benzedrine, 601 Benzene... 

FIGURE 3.20 The framework of a-bonds in benzene each carbon atom is sp2 hybridized, and the array of hybrid orbitals matches the bond angles (of 120°) in the hexagonal molecule. The bonds around only one carbon atom are labeled all the others are the same. 

Values found for interatomic distances and bond angles in the thirteen hydrocarbons studied are given in Table XIV. The carbon-carbon singlebond distance is found to have the constant value 1.54 = = 0.02 A., being unaffected by the presence of an adjacent double bond or benzene nucleus (provided that it does not form part of a conjugated system). The carbon-carbon double-bond distance in allene and acetylene has the value 1.34 A. This is 0.04 A. less than that formerly given by the table of covalent radii, which has accordingly been revised. The effect of the revision on the bond distance-resonance curve is discussed. 

Halogen % -bonding to benzene ring i Distances to six ring carbons k Distances to two carbon atoms 1 Distance from Br to aromatic plane m C-Br - X angle... 

Arynes present structural features of some interest. They clearly cannot be acetylenic in the usual sense as this would require enormous deformation of the benzene ring in order to accommodate the 180° bond angle required by the sp1 hybridised carbons in an alkyne (p. 9). It seems more likely that the delocalised 7i orbitals of the aromatic system are left largely untouched (aromatic stability thereby being conserved), and that the two available electrons are accommodated in the original sp2 hybrid orbitals (101) ... 

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