This structure is an accepted model for benzene. Note that the double bonds are placed between the 1-2, 3-4, and 5-6 carbons. Let’s start with the left hand benzene molecule and label the carbon atoms, clockwise, from 1 to 6. To illustrate this concept refer to the next Figure, which presents two different benzene molecules side-by-side. However, this picture does not really provide an accurate interpretation of the real benzene molecule. The structure is known as the famous, or perhaps infamous, benzene ring, and is an accepted model for benzene. Note that the model pictured is a hexagonal ring of carbon atoms with alternating (conjugated) double bonds. Benzene is a resonance structure that has a degree of chemical stability greater than what is expected of a compound with the structure illustrated here. The Structure of Benzeneīenzene is the classic example of an aromatic molecule. Before explaining why, it would be best to first explain the structure of benzene, which is the classic model of an aromatic or resonance compound. In reality the term alternating pi bonding orbitals is not really correct. Resonance is the result of alternating pi bonding orbitals that are present in the benzene ring structures that make up each graphene layer (keep in mind that graphite does not contain benzene). The unexpected stability is known as resonance energy. Substances that exhibit resonance have a degree of chemical stability not expected. Graphite can be thought of as being low in energy right from the start and this low chemical potential energy is the direct result of a unique bonding effect called aromaticity or resonance.
Some resonance structures are more favorable than others.One of graphite’s primary attributes is its high degree of thermal and chemical stability, i.e., its inertness. A molecule that has several resonance structures is more stable than one with fewer. The net sum of valid resonance structures is defined as a resonance hybrid, which represents the overall delocalization of electrons within the molecule. Resonance structures are used when one Lewis structure for a single molecule cannot fully describe the bonding that takes place between neighboring atoms relative to the empirical data for the actual bond lengths between those atoms. These structures are written with a double-headed arrow between them, indicating that none of the Lewis structures accurately describes the bonding but that the actual structure is an average of the individual resonance structures.
Resonance is a mental exercise and method within the Valence Bond Theory of bonding that describes the delocalization of electrons within molecules. Some molecules have two or more chemically equivalent Lewis electron structures, called resonance structures. Single bonds, double bonds, triple bonds, +1 charges, -1 charges, these are our limitations in explaining the structures, and the true forms can be in between - a carbon-carbon bond could be mostly single bond with a little bit of double bond character and a partial negative charge, for example. Resonance structures is a mechanism that allows us to use all of the possible resonance structures to try to predict what the actual form of the molecule would be. The best measurements that we can make of benzene do not show two bond lengths - instead, they show that the bond length is intermediate between the two resonance structures. One would expect the double bonds to be shorter than the single bonds, but if one overlays the two structures, you see that one structure has a single bond where the other structure has a double bond.
0 kommentar(er)
