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Review of Lewis Bonding Theory V. Properties of Molecules A. Ionic Bonding A. Acidity of Organic Molecules B. Covalent Bonding 1. Bronsted–Lowry Acidity 1. Multiple Bonding a) Review of AcidBase Equations 2. Formal Charge b) Acidity Trends C. ShortHand for Chemists i) Attached Atom 1. LineAngle Formulas ii) Inductive Effects 2. Dashes and Wedges iii) Hybridization 3. Curved Arrow Formalism iv) Resonance II. Resonance 2. Lewis Acidity A. Drawing Resonance Structures B. Bond Lengths B. Energy of Resonance Structures C. Bond Strengths C. Structure and Reactivity from Resonance VI. Alkanes III. Review of Molecular Orbital Theory A. Molecular Formulas A. Atomic Orbitals 1. Degrees of Unsaturation B. SigmaBonding 2. Constitutional Isomers C. PiBonding B. IUPAC Nomenclature D. VSEPR Theory C. Conformational Analysis IV. HybridizationLCAO 1. Ethane A. sp Hybridization a) Newman Projections B. sp2 Hybridization 2. Propane C. sp3 Hybridization 3. Butane 1. Rotation of Ethane versus EthyleneReview of Lewis Bonding Theory V. Properties of Molecules A. Ionic Bonding A. Acidity of Organic Molecules B. Covalent Bonding 1. Bronsted–Lowry Acidity 1. Multiple Bonding a) Review of AcidBase Equations 2. Formal Charge b) Acidity Trends C. ShortHand for Chemists i) Attached Atom 1. LineAngle Formulas ii) Inductive Effects 2. Dashes and Wedges iii) Hybridization 3. Curved Arrow Formalism iv) Resonance II. Resonance 2. Lewis Acidity A. Drawing Resonance Structures B. Bond Lengths B. Energy of Resonance Structures C. Bond Strengths C. Structure and Reactivity from Resonance VI. Alkanes III. Review of Molecular Orbital Theory A. Molecular Formulas A. Atomic Orbitals 1. Degrees of Unsaturation B. SigmaBonding 2. Constitutional Isomers C. PiBonding B. IUPAC Nomenclature D. VSEPR Theory C. Conformational Analysis IV. HybridizationLCAO 1. Ethane A. sp Hybridization a) Newman Projections B. sp2 Hybridization 2. Propane C. sp3 Hybridization 3. Butane 1. Rotation of Ethane versus EthyleneReview of Lewis Bonding Theory V. Properties of Molecules A. Ionic Bonding A. Acidity of Organic Molecules B. Covalent Bonding 1. Bronsted–Lowry Acidity 1. Multiple Bonding a) Review of AcidBase Equations 2. Formal Charge b) Acidity Trends C. ShortHand for Chemists i) Attached Atom 1. LineAngle Formulas ii) Inductive Effects 2. Dashes and Wedges iii) Hybridization 3. Curved Arrow Formalism iv) Resonance II. Resonance 2. Lewis Acidity A. Drawing Resonance Structures B. Bond Lengths B. Energy of Resonance Structures C. Bond Strengths C. Structure and Reactivity from Resonance VI. Alkanes III. Review of Molecular Orbital Theory A. Molecular Formulas A. Atomic Orbitals 1. Degrees of Unsaturation B. SigmaBonding 2. Constitutional Isomers C. PiBonding B. IUPAC Nomenclature D. VSEPR Theory C. Conformational Analysis IV. HybridizationLCAO 1. Ethane A. sp Hybridization a) Newman Projections B. sp2 Hybridization 2. Propane C. sp3 Hybridization 3. Butane 1. Rotation of Ethane versus EthyleneReview of Lewis Bonding Theory V. Properties of Molecules A. Ionic Bonding A. Acidity of Organic Molecules B. Covalent Bonding 1. Bronsted–Lowry Acidity 1. Multiple Bonding a) Review of AcidBase Equations 2. Formal Charge b) Acidity Trends C. ShortHand for Chemists i) Attached Atom 1. LineAngle Formulas ii) Inductive Effects 2. Dashes and Wedges iii) Hybridization 3. Curved Arrow Formalism iv) Resonance II. Resonance 2. Lewis Acidity A. Drawing Resonance Structures B. Bond Lengths B. Energy of Resonance Structures C. Bond Strengths C. Structure and Reactivity from Resonance VI. Alkanes III. Review of Molecular Orbital Theory A. Molecular Formulas A. Atomic Orbitals 1. Degrees of Unsaturation B. SigmaBonding 2. Constitutional Isomers C. PiBonding B. IUPAC Nomenclature D. VSEPR Theory C. Conformational Analysis IV. HybridizationLCAO 1. Ethane A. sp Hybridization a) Newman Projections B. sp2 Hybridization 2. Propane C. sp3 Hybridization 3. Butane 1. Rotation of Ethane versus EthyleneReview of Lewis Bonding Theory V. Properties of Molecules A. Ionic Bonding A. Acidity of Organic Molecules B. Covalent Bonding 1. Bronsted–Lowry Acidity 1. Multiple Bonding a) Review of AcidBase Equations 2. Formal Charge b) Acidity Trends C. ShortHand for Chemists i) Attached Atom 1. LineAngle Formulas ii) Inductive Effects 2. Dashes and Wedges iii) Hybridization 3. Curved Arrow Formalism iv) Resonance II. Resonance 2. Lewis Acidity A. Drawing Resonance Structures B. Bond Lengths B. Energy of Resonance Structures C. Bond Strengths C. Structure and Reactivity from Resonance VI. Alkanes III. Review of Molecular Orbital Theory A. Molecular Formulas A. Atomic Orbitals 1. Degrees of Unsaturation B. SigmaBonding 2. Constitutional Isomers C. PiBonding B. IUPAC Nomenclature D. VSEPR Theory C. Conformational Analysis IV. HybridizationLCAO 1. Ethane A. sp Hybridization a) Newman Projections B. sp2 Hybridization 2. Propane C. sp3 Hybridization 3. Butane 1. Rotation of Ethane versus Ethylene
5.12 Spring 2003 Review Session: Exam #1 I Review of Lewis Bonding Theory A Ionic Bonding B Covalent Bonding Multiple Bonding Formal Charge C Short-Hand for Chemists Line-Angle Formulas Dashes and Wedges Curved Arrow Formalism II Resonance A Drawing Resonance Structures B Energy of Resonance Structures C Structure and Reactivity from Resonance III Review of Molecular Orbital Theory A Atomic Orbitals B Sigma-Bonding C Pi-Bonding D VSEPR Theory IV Hybridization/LCAO A sp Hybridization B sp2 Hybridization C sp3 Hybridization Rotation of Ethane versus Ethylene V Properties of Molecules A Acidity of Organic Molecules Bronsted–Lowry Acidity a) Review of Acid/Base Equations b) Acidity Trends i) Attached Atom ii) Inductive Effects iii) Hybridization iv) Resonance Lewis Acidity B Bond Lengths C Bond Strengths VI Alkanes A Molecular Formulas Degrees of Unsaturation Constitutional Isomers B IUPAC Nomenclature C Conformational Analysis Ethane a) Newman Projections Propane Butane You need to be able to: I Review of Lewis Bonding Theory A Ionic Bonding B Covalent Bonding Multiple Bonding Formal Charge C Short-Hand for Chemists Line-Angle Formulas Dashes and Wedges Curved Arrow Formalism Provide all of the valid Lewis structures for the following molecules CH2N2 C4H8 • Provide Lewis structures and line angle formulas for given molecular formulas Don't forget lone pairs and formal charges! • Draw/interpret 3-D structures with dashes and wedges • Draw curved arrows to represent simple reaction mechanisms Hint: You will frequently start an arrow on a negative charge (electrons!) , but never start an arrow on a positive charge (no electrons!) a) Provide a mechanism for the following reaction CH3CO2H H3C O Convert the following to line angle formulas (CH3)3CCHCH2 H2C Cl H3C O CH3 Cl b) Label the electrophile and the nucleophile (CH3)2C(OH)CH2CH(CH3)2 II Resonance A Drawing Resonance Structures B Energy of Resonance Structures C Structure and Reactivity from Resonance For each pair, circle the most stable resonance structure, and use curved arrows to convert the structure on the left to the structure on the right O O You need to be able to: • Recognize resonance structures • Interconvert resonance structures • Predict relative energies and importance • Predict reactivity/physical properties using resonance structures Hint: Generating charges is bad!! • When you start with a neutral molecule, don't generate more than two formal charges • When you start with a charged molecule, don't generate any other formal charges Delocalization = Stabilization O O H3 C N CH2 H3 C H3 C CH3 CH3 CH3 O N H O CH3 H3 C Provide all relevant resonance structures for the following molecules, and rank their energies H O H N H O CH3 H3C CH3 N III Review of Molecular Orbital Theory A Atomic Orbitals B Sigma-Bonding C Pi-Bonding D VSEPR Theory IV Hybridization/LCAO A sp Hybridization B sp2 Hybridization C sp3 Hybridization Rotation of Ethane versus Ethylene Draw the bonding and anti-bonding orbitals resulting from the combination of two py orbitals along the x-axis Label any nodes Is this σ- or π-overlap? Try to the same with a px and a py orbital Why doesn't this work? You need to be able to: • • • • • • Draw atomic orbitals (s, p) Draw hybrid orbitals (sp, sp2, sp3) Differentiate between σ- and π-bonding Assign hybridization to atoms in a molecule Predict approximate bond angles Draw simple molecular orbital pictures a) Draw a molecular orbital picture of the following molecule H3C CH3 b) Use the picture from part a to explain why the following equilibrium does not occur H3C CH3 H3C CH3 You need to be able to: V Properties of Molecules A Acidity of Organic Molecules Bronsted–Lowry Acidity a) Review of Acid/Base Equations b) Acidity Trends i) Attached Atom ii) Inductive Effects iii) Hybridization iv) Resonance Lewis Acidity B Bond Lengths C Bond Strengths • Correlate Ka, pKa, and acidity • Rank relative acidities and explain your reasoning • Differentiate between Bronsted-Lowry and Lewis acids and bases • Draw mechanisms for acid-base reactions • Rank bond lengths and strengths based on bond order Rank each series by acidity (1 = most acidic) Which of the following molecules can act as a Lewis base? Why? Me3N BF3 H2O CH4 a) HO H H2N H b) O The following pair can undergo a BronstedLowry or a Lewis acid-base reaction Provide the products for both, and use curved arrows to provide the reaction mechanisms H3C CH3 O CH3 VI Alkanes A Molecular Formulas Degrees of Unsaturation Constitutional Isomers B IUPAC Nomenclature C Conformational Analysis Ethane a) Newman Projections Propane Butane H H3C O O H H3C O H c) HC C H H H2C CH • Draw constitutional isomers for a given molecular formula • Calculate degrees of unsaturation • Draw structures corresponding to IUPAC names • Draw Newman projections • Determine relative energies of rotational conformers Know the rotational energy values on the handout! • Draw potential energy diagrams for bond rotations For each molecular formula, calculate the degrees of unsaturation and draw two possible constitutional isomers C3H6 O O You need to be able to: Draw all of the constitutional isomers of C5H12 and name them using IUPAC nomenclature C7H12 F3C H H3C CH2 O HS H a) Approximate the barrier to rotation around the C2–C3 bond of 2,2-dimethylbutane Draw Newman projections to illustrate your answer b) Draw a potential energy diagram for rotation around theC2–C3 bond of 2,2-dimethylbutane C5H6 5.12 Spring 2003 Review Session: Exam #2 VI Alkanes A Molecular Formulas Degrees of Unsaturation Constitutional Isomers B IUPAC Nomenclature C Conformational Analysis Ethane a) Newman Projections Propane Butane VII Cycloalkanes A Ring Size and Strain B Cyclopropane C Cyclobutane D Cyclopentane E Cyclohexane Conformational Analysis a) Drawing Chairs b) Ring Flip Mono-Substituted Cyclohexane a) Axial versus Equatorial: A-Values Di-Substituted Cyclohexane a) Cis/Trans Isomerism b) Preferred Conformers Bicyclic Ring Systems VIII Stereochemistry A Stereoisomers You need to be able to: VI Alkanes A Molecular Formulas Degrees of Unsaturation Constitutional Isomers B IUPAC Nomenclature C Conformational Analysis Ethane a) Newman Projections Propane Butane • Draw constitutional isomers for a given molecular formula • Calculate degrees of unsaturation • Draw structures corresponding to IUPAC names • Draw Newman projections • Determine relative energies of rotational conformers Know the rotational energy values on the handout! • Draw potential energy diagrams for bond rotations Draw all of the constitutional isomers of C5H12 and name them using IUPAC nomenclature For each molecular formula, calculate the degrees of unsaturation and draw two possible constitutional isomers C7H12 C3H6 B Chirality and Stereocenters C Enantiomers Cahn–Ingold–Prelog Convention (R/S) Optical Activity Description of Samples D Diastereomers Cis/Trans Isomers (Geometric) Molecules with >1 Stereocenter IX Free Radical Reactions A Chlorination of Methane Mechanism B Review of Thermodynamics C Review of Kinetics D Reaction-Energy Diagrams Thermodynamic Control Kinetic Control Hammond Postulate Multi-Step Reactions Chlorination of Methane E Chlorination of Propane Inequivalent Hydrogens (1°,2°,3°) Relative Reactivity Selectivity F Bromination of Propane Selectivity (Hammond Postulate) G Radical Stability H General Selectivity of Radical Halogenations C5H6 a) Approximate the barrier to rotation around the C2–C3 bond of 2,2-dimethylbutane Draw Newman projections to illustrate your answer b) Draw a potential energy diagram for rotation around theC2–C3 bond of 2,2-dimethylbutane *The solutions for these problems can be found in the key for the first review session VII Cycloalkanes A Ring Size and Strain B Cyclopropane C Cyclobutane D Cyclopentane E Cyclohexane Conformational Analysis a) Drawing Chairs b) Ring Flip Mono-Substituted Cyclohexane a) Axial versus Equatorial: A-Values Di-Substituted Cyclohexane a) Cis/Trans Isomerism b) Preferred Conformers Bicyclic Ring Systems You need to be able to: • Provide the approximate ring strains and preferred conformations of the rings discussed in class • Analyze ring strain in terms of torsional and angle strain • Draw Newman projections to compare conformations of cycloalkanes • Draw and flip cyclohexane chairs Be sure you carefully differentiate between axial and equatorial bonds • Provide the details of a cyclohexane ring flip • Use A-values and diaxial interactions to predict the preferred conformers of substituted cyclohexanes Know your A-values! • Draw and differentiate between cis- and trans-isomers Draw chair conformers for cis- and trans-decalin Which would you expect to be more stable? Draw the two possible chairs for each molecule, and indicate the preferred conformer Me Me Et Me Me H H H H cis trans Et Which molecule would you expect to have the largest conformational preference Why? VIII Stereochemistry A Stereoisomers B Chirality and Stereocenters C Enantiomers Cahn–Ingold–Prelog Convention (R/S) Optical Activity Description of Samples D Diastereomers Cis/Trans Isomers (Geometric) Molecules with >1 Stereocenter Using Newman projections, predict the energy difference between the two Hint: Look for gauchebutane interactions in the higher energy structure You need to be able to: • Recognize stereoisomers: enantiomers & diastereomers • Draw all possible stereoisomers for a given molecule: Remember the 2n rule • Determine whether molecules are chiral or achiral: a) Count stereocenters; b) Look for mirror planes; c) Compare mirror images • Recognize meso compounds • Assign R/S stereochemistry to stereocenters • Correlate chirality with optical activity • Describe ratios of enantiomers using optical activity ( optically pure, racemic, etc.) Draw all of the stereoisomers of 1,2- and 1,3dimethylcyclohexane Assign each stereocenter as R or S How many are chiral? Achiral? Try to draw a chiral stereoisomer of 1,4dimethylcyclohexane Can you it? Why or why not? Practice assigning R and S stereochemistry until you feel like your head will explode! There are ample examples in the book and lecture All of the above molecules are achiral; however, hexahelicene (below) is chiral Why? Hexahelicene IX Free Radical Reactions A Chlorination of Methane Mechanism B Review of Thermodynamics C Review of Kinetics D Reaction-Energy Diagrams Thermodynamic Control Kinetic Control Hammond Postulate Multi-Step Reactions Chlorination of Methane E Chlorination of Propane Inequivalent Hydrogens (1°,2°,3°) Relative Reactivity Selectivity F Bromination of Propane Selectivity (Hammond Postulate) G Radical Stability H General Selectivity of Radical Halogenations You need to be able to: • Write a complete mechanism for a free radical chain reaction Use fishhook arrows! • Draw and completely label a reaction-energy diagram • Determine the rate-determining step of a multi-step reaction-energy diagram • Differentiate between transition states and intermediates • Differentiate between kinetic and thermodynamic control • Use the Hammond postulate to predict whether a kinetically controlled transformation will be selective • Use BDEs to estimate ∆H and ∆G • Rate the stability of radicals, and explain • Predict the products of radical bromination • Calculate the relative reactivity of inequivalent hydrogens from reaction selectivities Radical stability is strongly dependent on substitution (3° > 2° > 1° > methyl) Why? Draw pictures to illustrate Draw resonance structures to explain the selectivity of the following reaction CH3 Br2 Provide a complete reaction mechanism for the bromination in number Draw a complete reaction energy diagram for the propagation steps You can assume that a benzylic C–Br bond is approximately 68 kcal/mol Rank the stability of each of the following radicals (1 = most stable) Radicals with the same energy should be given the same number Br hv H3C H3C CH3 Aside from resonance, why isn't the following product observed? CH3 H3C H3C CH3 CH3 Br ... combination of two py orbitals along the x-axis Label any nodes Is this σ- or π-overlap? Try to the same with a px and a py orbital Why doesn't this work? You need to be able to: • • • • • • Draw atomic