CHEM 334 1st Edition Lecture 1Outline of Current Lecture I. Review of Definitionsa. Saturated and Unsaturatedb. π bondsc. Resonance StructuresII. Dienesa. Conjugatedb. CumulatedIII. Absorption Spectroscopya. HOMO and LUMOCurrent LectureReview of Definitions from Organic 1:Saturated and unsaturated compounds: Compounds that consist of single carbon to carbon bonds (alkanes) are considered saturated compounds. Saturated compounds undergo substitution reactions. Compounds that contain double or triple carbon to carbon bonds are called unsaturated compounds. These unsaturated compounds(alkenes and alkynes) undergo addition reactions. Π bonds: A π bond is a covalent bond formed between two atoms’ unbound p-orbitals.Resonance Structure: Resonance structures are different forms or structures of the same molecule. When drawing resonance structures, we use curved arrows to show where the electrons are moving around the structure. When drawing resonance structures, remember that arrows start where electrons were and points to where they are supposed to end up.Dienes:A diene is a carbon-carbon chain with two double bonds. Dienes can be conjugated, unconjugated, or cumulated. Conjugated:Conjugated dienes are dienes with two or more adjacent π bonds separated by only one single bond. Basically, conjugated compounds have alternating single and double bonds. However, these NEED at least two π bonds. In a conjugated system, you have π bond overlap. Each carbon has a π orbital associated with it. They can also have a p orbital adjacent to a π bond. Conjugated systems are importantbecause we can do resonance structures with them. Just because a molecule has more than two double These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.bonds, it does not necessarily mean that it is conjugated. For a compound to be conjugated, it has to have resonance.Example: // \ // _ /+\ // _/\\ /+Conjugated dienes can be s-cis or s-trans configuration. S-trans is more stable in conformation than s-cis, meaning it is also lower in energy. Cumulated:Cumulated Dienes are two double bonds directly attached to the same carbon. Cumulated compounds are unconjugated. Absorbance Spectroscopy:Absorbance spectroscopy measures radiation and absorption as a function of wavelength(λ). Molecules can absorb energy from light and get excited. Conjugated systems absorb ultraviolet and visible light. Compounds absorb excitation light and let other light pass through. The colors that you see are from the light NOT absorbed. If you see the color white, nothing is absorbed. If you see the color black, all light is absorbed. HOMO and LUMO:The interaction of any two molecular orbitals produces two new orbitals, one of higher energy than the original ones and one of lower energy (the bonding orbital). With interacting molecular orbitals, the two that interact are generally the highest energy occupied molecular orbital (HOMO) of one molecule and the lowest energy unoccupied molecular orbital (LUMO) of the other molecule. The longer the conjugation, the less energy is required to excite one electron to the LUMO. The shorter the wavelength, the greater the energy. Therefore, the less conjugated the compound, the shorter the wavelength it
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