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Transcript
OUTLINE OF 2nd MIDTERM MATERIAL Chapter 4: Alkanes (Cycloalkanes) –review from 1st midterm material Cyclohexanes: chair and boat forms; equatorial and axial bonds of cyclohexanes Mono-substituted cyclohexanes: equatorial substituents are more stable (1,3-diaxial interactions); tert-butylcyclohexane Disubstituted cyclohexanes: cis/trans-isomerism; comparison of stability (the fewer are the axial substituents, the more stable is the disubstituted cyclohexane. Fused rings (cis and trans decalins) Chapter 5: Stereochemistry Stereoisomers (drawing 3-D molecules in “wedged” and “dashed” bonds; Fischer structures) Enantiomers (physical properties); chirality; stereogenic (chiral) centers; racemic mixtures Optical activity; criteria for optical activity; R/S Configurations Molecules with more than one stereogenic center; diastereoisomers; molecules with chiral centers, but with a plane of symmetry (thus optically inactive, “meso” form) Chapter 6: Understanding Organic Reactions Types of organic reactions Bond formation and bond cleavage (homolytic and heterolytic) Reactive Intermediates Bond Dissociation Energies (BDE) Thermodynamics: Equilibria and free energy changes; enthalpy and entropy Reaction/Energy Diagrams Kinetics: Reaction rates Catalysts/Enzymes Chapter 7: Alkyl Halides – SN1 and SN2 Reactions Nucleophiles (in their free base and anionic forms) SN2 Reactions (stereochemical outcomes) When site of attack is a chiral center When site of attack is not a chiral center Leaving Group abilities SN1 Reactions (stereochemical outcomes) Carbocations; factors which determine carbocation stability Hammond Postulate Competition between SN1 and SN2 Reactions Conditions which favor SN2 reactions: uncrowded reaction site; strong nucleophiles; aprotic polar solvents Conditions which favor SN1 reactions: potential to form stable a carbocation (tertiary alkyl halides); weak, non-ionic nucleophiles Chapter 8: Alkyl Halides – Dehydrohalogenation (E1, and E2) Reactions Site of attack in elimination reactions Types of bases Bulky, non-nucleophilic (strong) bases Weak base nucleophiles Regioselectivity (and stereoselectivity) in elimination reactions (Zaytzeff Rule) Stereochemical requirements in E2 reactions (application to cyclic systems) Competition between Nucleophilic Substitution and Elimination Reactions: SN1, E1 reactions generally occur together Conditions which favor E2 reactions: more substituted alkyl halides (why?) –in contrast to SN2 reactions-; bulky bases Chapter 9: Alcohols and Ethers Structural features of alcohols Syntheses of alcohols through SN reactions Reactions of alcohols General Strategy: Converting –OH into a good LG (9.7A) SN1 type reactions: conversions of 3o alcohols into alkyl halides (9.11A) SN2 type reactions: Lewis acid –mediated (with SOCl2 and PBr3 -9.12) E type reactions: dehydration of alcohols (9.8)