CH 221 Edition 7 Lecture 20 Outline of Last Lecture I. EpoxidesII. OzonolysisIII. Addition of HydrogenIV. Stabilities of AlkenesV. Regioselective and Stereoselective ReactionsVI. Racemic MixtureOutline of Current Lecture VII. Formation of a Second Asymmetric CenterVIII. Syn and Anti AdditionIX. Hydroboration-OxidationX. AlkynesCurrent LectureVII. Formation of a second asymmetric center- When a reactant that has an asymmetric center forms a product that has a new asymmetric center, that product is a pair of diastereomers- Four stereoisomers are obtained if the reaction forms a carbocation intermediateVIII. Syn and anti addition- A pair of enantiomers result from syn addition- The addition of H2 is considered a syn addition- Syn addition to a Cis isomer forms only the erythro stereoisomers- If the substituents are the same, the erythro stereoisomer is a Meso compound- Syn addition of H2 to a trans isomer forms only the threo stereoisomer- If the substituents are the same, the Cis stereoisomer is a Meso compound- Cyclic alkenes are Cis unless they have at least eight ring atoms- The addition of peroxyacid is a syn addition- Syn addition to Trans isomers forms only Trans stereoisomers- If the substituents are the same, Cis stereoisomers are Meso compounds 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.- The addition of borane is a syn additionIX. Hydroboration-Oxidation is overall a syn addition of water- The addition of a halogen is an anti addition- Anti addition to a Cis isomer forms only Threo stereoisomer- If the substituents are the same, the Cis isomer is a Meso compound- If the substituents are the same, the erythro stereoisomer is a Meso compound- Anti addition to a Cis isomer forms only trans stereoisomersX. Alkynes- hydrocarbons that contain one or more carbon-carbon triple bonds- General formula CnH2 n−2 (acyclic) or CnH2 n−4 (cyclic)- The “yne” suffix is assigned to the lowest number possible- Substituents are assigned so the lowest number is in its name- Ex. 3-bromo-2-chloro-4-octyne- When there is two of the same functional group its ca led a diene- Ex. Propadiene- When there is a double bond and a triple bond in the same compound- Ex. 5-heptene-1-yne, 3-butyl-1-hexene-4-yne- Longest carbon chain (parent hydrocarbon) must contain both functional groups- When the same numbers are obtained for both functional groups, the double bond is assigned the lower number- Priorities of functional groups- Highest C=O > OH > NH2 > C=C > C (triple bond) C lowest- Alkynes have one sigma bond and two pi bonds formed by an sp-sp overlap- Alkynes are always linear and have a 180º bond
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