I. Nucleophilic Substitution of Allylic HalidesII. If conditions are suitable for carbocation formation, SN1 will occurI. Conjugated DienesII. Heat of HydrogenationCHEM 0320 1st Edition Lecture 3 Outline of Last Lecture I. Nucleophilic Substitution of Allylic Halides II. If conditions are suitable for carbocation formation, SN1 will occurIII. Rates IV. Allylic Anion Material Outline of Current Lecture I. Conjugated Dienes II. Heat of Hydrogenation III. Electrophilic Addition of Conjugated Dienes IV. The Rate Determining Step (RDS) Current LectureI. Conjugated Dienesa. NOTE*** naming: you must do on your own!!! b. “Conjugated” means 2 alkenes joined by a single bondi. Conjugated dienes are stabilized by electron density distribution ii. In Conjugated alkene systems only, alkene functional groups are interacting with each other, adding stability! c. Density between spread out 4 pi e- distributed over 3 bond axesII. Heat of Hydrogenation for allylic substrate vs. conjugated dienea. For allylic substrate, heat of hydrogenation to form an alkane is LOWER than the heat of hydrogenation for a conjugated diene to form an alkene i. HIGHER ∆H for conjugated diene because you’re hydrogenating 2 separate pi bonds! b. Comparing structures of conjugated dienes in terms of stability:i. A conjugated diene is MORE STABLE than a non-conjugated dienea. Stability is due to the pi-pi interaction of the pi bonds (distribution of electrons across the single bond axis) III. Electrophilic Addition of Conjugated Dienes a. Can occur with 1,2 regiochemistry OR 1,4 regiochemistry 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. **NOTE this naming system is NOT related to nomenclature numbers b. 1,2 adduct vs. 1,4 adduct as two possible products: i. 1,2 adduct: (below)i) 1,4 adduct: (below)(1) Formed from the resonance structure, allowing for a second point of attack by Cl-, which will form a different product called the 1,4 adduct.2) The Rate Determining Step (RDS) and Product Determining Step (PDS) for ELECTROPHILIC ADDITION to conjugated diene systema) The RDS: i) Formation of the allylic carbocation (1) At this point, identify resonance forms, and understand that two carbons do NOTshare the partial positive charge equally. (a) The more stable carbocation is bonded to another electron donating group.b) The PDS: i) Formation of two regioisomers(1) They are formed at the SAME RATE! Questions to ask yourself: (a) Which regioisomer is the more stable product? (i) You answer this by looking at the rate-determining step. The thermodynamically more stable product is the product that formed from the more stable carbocationc) Low Temp. vs. High Temp. vs. Long Time (below is representative of above example)3) NOTE** to know major product, you must look at partial positives to know major
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