CHE 3331 Chapter Notes - Chapter 15: Ion, Allyl Group, Alkoxy Group

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16 Dec 2017

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Chapter 15: conjugated systems orbital symmetry, and ultraviolet. Conjugated double bonds: double bonds separated by just one single bond. Isolated double bonds: double bonds with two or more single bonds between them. Systems with conjugation tend to be more stable than similar systems with isolated double bonds. 15-3 molecular orbital picture of a conjugated system: Bonding molecular orbital: the lobes that overlap in the bonding region between nuclei are in phase. Constructive overlap: an important feature of all bonding molecular orbitals in which the overlapping lobes have the same phase (+, +) or (-,-) Antibonding molecular orbital: lobes of opposite phase overlap in the bonding region (+,-) or. Destructive overlap: causes the cancelling of the wave function in the bonding region. Node: present in the antibonding mo, a region of 0 electron density where the positive and negative phases exactly cancel out.

Related Questions

Benzene is an organic chemical compound with the molecular formula C6H6. In the benzene molecule, carbon atoms form a ring with alternating single and double bonds connecting them. Thus, each individual carbon atom forms one ? bond with another carbon atom and one ? and one ? bond with another carbon atom. Each carbon atom also forms one ? bond with a hydrogen atom. Identify which types of orbitals overlap to form the bonds between the atoms in a benzene molecule. Drag the appropriate labels to their respective targets.

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Chemical bonds are formed by linear combinations of atomic orbital's. These atomic orbital's should have compatible energies. An axial overlap of these orbitals results in the formation of a sigma bond, whereas a lateral overlap results in the formation of a pi bond. When two atomic orbitai's on different atoms approach each other, two molecular orbital's are formed: one bonding molecular orbital and one antibonding molecular orbital. The bonding molecular orbital has a lower energy than the corresponding atomic orbital's: antibonding orbital's have higher energies than the corresponding atomic orbital's. An example using the hydrogen molecule is shown here. However, the same rule applies to systems with multiple atomic orbital's. For each atomic orbital that overlaps, one molecular orbital must form. In the diagram below. 1s orbitais from two hydrogen atoms combine to form one bonding sigma1 orbital and one antibonding orbital. The total number of bonding and antibonding orbital's is always equal to the number of orbital's that overlap. Similarly, molecular orbital's can also be formed by the overlapping of hybrid orbital's. The hybrid orbital's are formed by the linear combination of different atomic orbital's of nearly equal energy on the same atom. The atomic orbital's of nearly equal energy undergo a process of mixing and reorientation to form new orbital's of lower energy. This process is called hybridization For example, hybridization of one s and two p orbital's on an atom forms three sp2 hybrid orbital's. Benzene is an organic chemical compound with the molecular formula C6H6. In the benzene molecule, carbon atoms form a ring with alternating single and double bonds connecting them. Thus, each individual carbon atom forms one sigma bond with another carbon atom and one sigma and one pi bond with another carbon atom. Each carbon atom also forms one sigma bond with a hydrogen atom. Identify which types of orbital's overlap to form the bonds between the atoms in a benzene molecule.

The molecular orbitals associated with the Ï-bonding MOs insquare cyclobutadiene (C4H4) are, like benzene, form by overlap ofa single p-orbital on each carbon atom that is not involved in thesigma-bonding network of the molecule. These p-orbitals pointperpendicularly with respect to the plane defined by the carbonatoms. There is no central atom, so the only interactions thatmatter are between the p-orbitals among themselves. These MOs haveexactly the same phase relationship as the SALCs you just made inquestion 1. i) Use your results from question 1 to draw the fourÏ-orbitals of C4H4. ii) Use the idea that the energy of a MOincreases with number of new nodes made during bonding (i.e. nodesnot already present in initial AO functions) to sketch a molecularorbital energy level diagram for the Ï-molecular orbitals of C4H4.Remember that, by definition, degenerate orbitals are identicalexcept for trivial rotation in space, and have identical energy.iii) Fill the MOs with the electrons from the atomic p-orbitalsthat you used to form the Ï-MOs of C4H4. Use your diagram todetermine the overall bond order by considering each doublyoccupied bonding MO to contribute 1, each nonbonding orbital 0 andeach antibonding orbital -1. The result would be divided by 4 C-Cbonds to get the average contribution to each C-C bond fromÏ-bonding, which then should be added to a Ï-bonding contributionof 1.0. iv) Repeat step (iii) for the dication C4H4 2+ to determinethe net bond order for this species. Why do you think you got thisvalue? v) Predict which of C4H4 and C4H4 2+ could be observed byESR spectroscopy. vi) Which of C4H4 2+ and C4H4 is more likely tobe susceptible to electrophilic attack.

CHE 3331 Chapter Notes - Chapter 15: Ion, Allyl Group, Alkoxy Group

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