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Ch.11 - Chemical Bonding II: Molecular Shapes, VSEPR & MO Theory
Chapter 11, Problem 92d

The genetic code is based on four different bases with the structures shown here. Assign a geometry and hybridization to each interior atom in these four bases. d. guanine
Chemical structure of guanine with labeled atoms for hybridization analysis.

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Identify the hybridization of each interior atom by counting the number of sigma bonds and lone pairs around the atom.
For atom 1 (carbonyl carbon), it has 3 sigma bonds and no lone pairs, so it is sp2 hybridized with a trigonal planar geometry.
For atom 2 (nitrogen), it has 2 sigma bonds and 1 lone pair, so it is sp2 hybridized with a bent geometry.
For atom 3 (carbonyl carbon), it has 3 sigma bonds and no lone pairs, so it is sp2 hybridized with a trigonal planar geometry.
For atom 4 (carbon), it has 3 sigma bonds and no lone pairs, so it is sp2 hybridized with a trigonal planar geometry.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hybridization

Hybridization is the concept of mixing atomic orbitals to form new hybrid orbitals that can accommodate the bonding requirements of atoms in a molecule. In guanine, for example, carbon atoms typically exhibit sp2 hybridization, allowing for the formation of planar structures with double bonds, while nitrogen atoms may show sp3 hybridization, accommodating lone pairs and bonding.
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Molecular Geometry

Molecular geometry refers to the three-dimensional arrangement of atoms within a molecule. The geometry is determined by the hybridization of the central atom and the number of bonds and lone pairs surrounding it. For guanine, the arrangement of atoms leads to a specific geometry that influences its interactions and functions in biological systems.
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Resonance Structures

Resonance structures are different ways of drawing a molecule that represent the same arrangement of atoms but differ in the distribution of electrons. In guanine, resonance is important for understanding the delocalization of electrons in the aromatic ring and the stability of the molecule, which is crucial for its role in the genetic code.
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