CHEM 3410 1st Edition Lecture 1Outline of Current LectureI. Introduction to Conjugated DienesA. Conjugated vs NonconjugatedB. Definition of a Conjugated DieneC. Relative StabilityII. Electrophilic Addition RecapIII. Synthesis of Conjugated DienesIV. Electrophilic Addition to Conjugated DienesOutline of Next LectureV. Electrophilic Addition to Conjugated Dienes (Continued)VI. Kinetic vs Thermodynamic ControlCurrent LectureI. Introduction to Conjugated DienesA. Nonconjugated Recall from last semester that the presence of a single pi bond (a double bond) means that the carbons of the alkene are sp2 hybridized (containing s and p orbitals), and without pi bonds, thecarbon is sp3 hybridized (containing only s orbitals). The p orbitals in this diene do not overlap because they are separated by a central sp3 hybridized carbon; therefore, the molecule is a nonconjugated diene. The electrons are localized and unable to flow freely. B.1 Conjugated (Trans/E)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.In a conjugated diene, there will be four sp2 hybridized carbons in a row. A conjugated diene contains overlapping p orbitals from two alkenes that are connected to each other.The p orbitalsline up, allowing for this overlap, thus they are in conjugation. Furthermore, there are is a delocalization of electrons because of the overlap of p orbitals, allowing the electrons to move freely. Delocalization increases stability. Conjugated dienes are more stable than nonconjugated dienes.B.2. Conjugated (Cis/Z)Again, note the four sp2 carbons in a row. This is a conjugated diene. However, note the stereochemistry. Is it more stable than the previous conjugated diene? No.Cis is less stable than Trans due to reduced steric strain. When the molecules eclipse in a cis molecule, there is steric strain. That strain is reduced in the trans relationship because the largest groups are not eclipsing. Recall the rules of stability from last semester:> >C. Relative Stability (Cis/Trans Conjugated vs Nonconjugated)> >Again, Nonconjugated is less stable than Conjugated, and Cis is less stable than Trans. The increase of stability between nonconjugated and conjugated is due to the delocalization ofelectrons due to the overlap of p orbitals. The relative stability of tans vs cis is due to the decreased steric strain. Practice: Identify the Conjugated DienesIn this diene, there were three alkenes in a row for both conjugations. Note that they are in conjugation because the sp2 carbons of all alkenes in conjugation are bonded to each other without the interference of sp3 carbons. Also, note that the sp3 terminal carbon of the top conjugation was not included. The terminal sp3 carbon is not part of the conjugation.II. Electrophilic Addition RecapThe HBr is added "in excess"In the electrophilic addition of halogens to a conjugated diene will always form the radical alkyl halide, thus the halide will attach to the most substituted carbon (3° or below. It of course cannot attach to a 4° carbon.)*Ignore the plus signs. The Marvin sketch software did that.Again, in this example, you see the electrophilic addition of a halide to an alkene. The electrons of the double bond attack the hydrogen of HBr, (hence “electrophile”- lover of electrons) leaving a positively charged carbon. The electrons of the negatively charged bromine will attack the positively charged carbon, and attach. This is another example of electrophilic addition. Note that all products have the halide attach to the more highly substituted carbon from the original alkene. Remember MARKOVNIKOV’S RULE. The addition of the hydrogen atoms to one carbon atom in the alkene creates a positive charge on the other carbon in a manner which forms the more stable carbocation intermediate. More substituted, more stable. Carbocations are sp2 hybridized, allowing (R) AND (S) products,INVERSION FAVORED RACIMIZATION.You would get a mix of R and S products.Recall that in condition in which we would want to add Iodine to an alkene, we would also include H2SO4 in the reaction to make the reaction work. You may see NaI or KI, but this is due tothe physical properties and boundaries faced when using iodine in a practical setting. III. Synthesis of Conjugated DienesRecall that last semester, we learned two manners in which to create alkenes from alkyl halides: dehydration of water and dehydrohalogenation.In the example above, we note that the first step of the reaction occurs in a single, concerted step, similar to an E2 reaction (notice the strong, bulky nucleophile). The strong, bulky nucleophile attacks the Hydrogen, causing the electrons from the bond formed between it and the carbon of the cyclohexane to return to the system, creating a double bond. That overloads the carbon attached to the bromine, kicking the bromine off. Next, we react the substance with NBS and uv light to create a radical (the radical symbol is faint and hard to see.) The radical thenattracts a radical Bromine from the NBS, creating an alkyl halide. We then repeat the E2 elimination like step to create a conjugated diene. Remember that the conjugated diene is morestable, thus more favored than its less stable, nonconjugated counterpart.Recall dehydration. In this example, we reduced the single alkene to an anti-diol with the addition of OsO4 and pyridine. We take that a step further via dehydration with Al2O3 in heat, and get the conjugated diene AND the alkyne. The conjugated diene will be slightly more prevalent in your final product due its stability.VI. Electrophilic Addition to Conjugated DienesResonance gives us a second intermediate and a second product. The products are named “1,2 addition product” and “1,4 addition product” because of where we add things on the molecule. Hydrogen attaches to carbon one of the alkene as it is pulled on by the electrons from the double bond. Recall Markovnikov again – The carbocation forms that is more stable – that is why the Hydrogen attaches to “carbon 1.” The addition to 2 or 4 depends on resonance. The electrophile will attach to carbon 2 of the original alkene (the more stable, available carbon of the alkene from which we began), in the resonance structure, the electrophile will attach to carbon 4.For clarification, the resonance of the figures is displayed below with arrows of electron flow. Note that the