Question

1 (a) UsingVSEPR, predict each $\m… # Following is a structural formula of benzene, \(\mathrm{C}_{6} \mathrm{H}_{6}\), which we study in Chapter 21 . c1ccccc#1 (a) UsingVSEPR, predict each \(\mathrm{H}-\mathrm{C}-\mathrm{C}\) and \(\mathrm{C}-\mathrm{C}-\mathrm{C}\) bond angle in benzene. (b) State the hybridization of each carbon in benzene. (c) Predict the shape of a benzene molecule. (d) Draw important resonance contributing structures.

Short answer

The hybridization of the carbon atoms in benzene is sp2, and both the H-C-C and C-C-C bond angles are 120 degrees.

Step-by-step solution

Predict H-C-C and C-C-C bond angles using VSEPR theory

VSEPR (Valence Shell Electron Pair Repulsion) theory helps to predict the geometry of a molecule based on the repulsion between electron pairs in the valence shell of the central atom. In benzene, each carbon atom is bonded to two other carbon atoms and one hydrogen atom. Each carbon atom has three bonding electron pairs that repel each other. They arrange themselves in a planar geometry to minimize repulsion. For the H-C-C bond angle, since we have a planar geometry, the angle between H-C-C would be 120 degrees. For the C-C-C bond angle, since each carbon is connected to two other carbons, the angle between C-C-C would also be 120 degrees.

Determine the hybridization of each carbon in benzene

To determine the hybridization of each carbon atom, we need to look at the number of sigma bonds and electron domains around each carbon. Each carbon in benzene forms 3 sigma bonds, i.e., one with hydrogen and two with other carbon atoms. Therefore, it has 3 electron domains. When there are 3 electron domains, the hybridization is sp2. Thus, each carbon in benzene is sp2 hybridized.

Predict the shape of a benzene molecule

The shape of a benzene molecule can be determined based on the hybridization of the carbon atoms. As we know that all of the carbons are sp2 hybridized, it means they are arranged in a trigonal planar configuration around each carbon. The benzene molecule consists of a hexagonal ring of carbon atoms, with each carbon bonded to one hydrogen atom. Therefore, the shape of a benzene molecule is a planar hexagonal ring.

Draw important resonance contributing structures

Resonance structures help to represent the electron distribution in a molecule more accurately. Benzene has two resonance structures, where the double bonds between the carbon atoms alternate positions: Structure 1: 1 2 3 \=/ \=/ 6-C-C-C-4 \=/ \=/ 5 Structure 2: 1 2 3 %=/ %=/ 6-C-C-C-4 /%= /%= 5 In both resonance structures, the benzene ring has alternating double and single bonds. The actual electron distribution is a blend of these two resonance structures, with each C-C bond being an intermediate between a single bond and a double bond.