I. Types of Dienes best for Diels AlderII. Types of Dienophiles best for Diels AlderI. Weakening of electron resonance donation abilityII. Benzene and its structural and chemical propertiesIII. Predicting reactions of benzeneIV. NomenclatureI. Weakening of electron resonance donation abilitya. Competing resonancei. When there are many resonance structure possibilitiesb. Positive /positive interactionsi. If an atom attached to pi system has positive charge, it will not be resonance donor.II. Benzene and its structural and chemical propertiesa. Benzene does not have alternating pi bondsi. If this were the case, then it would have longer bond lengths between sigma bonds and shorter bond lengths between pi bonds, and would look much like a baseball plate.ii. Instead, 6 pi electrons are delocalized around the entire benzene ring, which is why chemists often draw benzene as a cyclohexane with a circle in the middle (right)1. Therefore all bonds are identical; there are no isolated pi bonds!b. The real structure is donut shaped.i. Pi electron density is moving above and below the internuclear plane, creating a “donut” shape, NOT like the cyclohexane chair conformation.c. If benzene did have a regular alkene structure with alternating pi bonds, it would undergo alkene reactions:i. However, when benzene is put in a reaction vessel with H-Br, there is no observed chemistry.ii. When a cycloalkane is put in a reaction vessel, chapter 12 chemistry occurs.III. Predicting reactions of benzenea. Benzene is unusually stable.i. If benzene had alternating pi bonds that were stabilized by resonance, the prediction for enthalpy change would be -78 kcalii. If benzene had alternating pi bonds without considering resonance, the enthalpy change is predicted to be around -87 kcal.iii. Hydrogenation reactions of benzene require a very large amount of energy, ∆H = about 50 kcal.1. Very endothermic; so a great amount of energy needs to be added to the system in order for benzene to undergo hydrogenation2. It’s over 30 kcal more stable than expected.3. This “extra stability” is called aromatic stabilizationa. Aromatic stabilization is NOT RESONANCE STABILIZATIONIV. Nomenclaturea. When benzene is a substituent, it is called a “phenyl” substituenti. Phenyl can be represented as “Ph” or “Ф” coming off parent chainb. An aryl group is a phenyl group with another substituent (i.e. alcohol, methyl, halide, etc.)c. You must be able to name the structure of diphenyl ketone, also known as benzophenone (common name)i. IUPAC: benzenol (do not need the “1” because it is implied)d. Bromobenzene is another structure you must know.i. (do not need the “1” in IUPAC name because it is implied)CHEM 0320 1st Edition Lecture 6Outline of Last Lecture I. Types of Dienes best for Diels Alder II. Types of Dienophiles best for Diels Alder Outline of Current Lecture I. Weakening of electron resonance donation ability II. Benzene and its structural and chemical properties III. Predicting reactions of benzene IV. Nomenclature Current LectureI. Weakening of electron resonance donation ability a. Competing resonance i. When there are many resonance structure possibilities b. Positive /positive interactions i. If an atom attached to pi system has positive charge, it will not be resonance donor. II. Benzene and its structural and chemical properties a. Benzene does not have alternating pi bonds i. If this were the case, then it would have longer bond lengthsbetween sigma bonds and shorter bond lengths between pibonds, and would look much like a baseball plate. ii. Instead, 6 pi electrons are delocalized around the entirebenzene ring, which is why chemists often draw benzene asa cyclohexane with a circle in the middle (right)1. Therefore all bonds are identical; there are no isolated pi bonds!b. The real structure is donut shaped. 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.i. Pi electron density is moving above and below the internuclear plane, creating a “donut” shape, NOT like the cyclohexane chair conformation. c. If benzene did have a regular alkene structure with alternating pi bonds, it would undergo alkene reactions: i. However, when benzene is put in a reaction vessel with H-Br, there is no observed chemistry. ii. When a cycloalkane is put in a reaction vessel, chapter 12 chemistry occurs. III. Predicting reactions of benzene a. Benzene is unusually stable. i. If benzene had alternating pi bonds that were stabilized by resonance, theprediction for enthalpy change would be -78 kcal ii. If benzene had alternating pi bonds without considering resonance, the enthalpy change is predicted to be around -87 kcal. iii. Hydrogenation reactions of benzene require a very large amount of energy, ∆H = about 50 kcal.1. Very endothermic; so a great amount of energy needs to be added to the system in order for benzene to undergo hydrogenation2. It’s over 30 kcal more stable than expected. 3. This “extra stability” is called aromatic stabilizationa. Aromatic stabilization is NOT RESONANCE STABILIZATIONIV. Nomenclature a. When benzene is a substituent, it is called a “phenyl” substituent i. Phenyl can be represented as “Ph” or “Ф” coming off parent chainb. An aryl group is a phenyl group with another substituent (i.e. alcohol, methyl, halide, etc.)c. You must be able to name the structure of diphenyl ketone, also known as benzophenone (common name)i. IUPAC: benzenol (do not need the “1” because it is implied) d. Bromobenzene is another structure you must know. i. (do not need the “1” in IUPAC name because it is